diff --git a/.github/workflows/checklocks.yml b/.github/workflows/checklocks.yml
deleted file mode 100644
index 5768cf05af634..0000000000000
--- a/.github/workflows/checklocks.yml
+++ /dev/null
@@ -1,34 +0,0 @@
-name: checklocks
-
-on:
-  push:
-    branches:
-      - main
-  pull_request:
-    paths:
-      - '**/*.go'
-      - '.github/workflows/checklocks.yml'
-
-concurrency:
-  group: ${{ github.workflow }}-${{ github.head_ref || github.run_id }}
-  cancel-in-progress: true
-
-jobs:
-  checklocks:
-    runs-on: [ ubuntu-latest ]
-    steps:
-      - name: Check out code
-        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
-
-      - name: Build checklocks
-        run: ./tool/go build -o /tmp/checklocks gvisor.dev/gvisor/tools/checklocks/cmd/checklocks
-
-      - name: Run checklocks vet
-        # TODO(#12625): add more packages as we add annotations
-        run: |-
-          ./tool/go vet -vettool=/tmp/checklocks \
-            ./envknob           \
-            ./ipn/store/mem     \
-            ./net/stun/stuntest \
-            ./net/wsconn        \
-            ./proxymap
diff --git a/.github/workflows/cigocacher.yml b/.github/workflows/cigocacher.yml
deleted file mode 100644
index 15aec8af90904..0000000000000
--- a/.github/workflows/cigocacher.yml
+++ /dev/null
@@ -1,73 +0,0 @@
-name: Build cigocacher
-
-on:
-  # Released on-demand. The commit will be used as part of the tag, so generally
-  # prefer to release from main where the commit is stable in linear history.
-  workflow_dispatch:
-
-jobs:
-  build:
-    strategy:
-      matrix:
-        GOOS: ["linux", "darwin", "windows"]
-        GOARCH: ["amd64", "arm64"]
-    runs-on: ubuntu-24.04
-    env:
-      GOOS: "${{ matrix.GOOS }}"
-      GOARCH: "${{ matrix.GOARCH }}"
-      CGO_ENABLED: "0"
-    steps:
-    - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
-    - name: Build
-      run: |
-        OUT="cigocacher$(./tool/go env GOEXE)"
-        ./tool/go build -o "${OUT}" ./cmd/cigocacher/
-        tar -zcf cigocacher-${{ matrix.GOOS }}-${{ matrix.GOARCH }}.tar.gz "${OUT}"
-
-    - uses: actions/upload-artifact@b7c566a772e6b6bfb58ed0dc250532a479d7789f # v6.0.0
-      with:
-        name: cigocacher-${{ matrix.GOOS }}-${{ matrix.GOARCH }}
-        path: cigocacher-${{ matrix.GOOS }}-${{ matrix.GOARCH }}.tar.gz
-
-  release:
-    runs-on: ubuntu-24.04
-    needs: build
-    permissions:
-      contents: write
-    steps:
-      - name: Download all artifacts
-        uses: actions/download-artifact@37930b1c2abaa49bbe596cd826c3c89aef350131 # v7.0.0
-        with:
-          pattern: 'cigocacher-*'
-          merge-multiple: true
-      # This step is a simplified version of actions/create-release and
-      # actions/upload-release-asset, which are archived and unmaintained.
-      - name: Create release
-        uses: actions/github-script@ed597411d8f924073f98dfc5c65a23a2325f34cd # v8.0.0
-        with:
-          script: |
-            const fs = require('fs');
-            const path = require('path');
-
-            const { data: release } = await github.rest.repos.createRelease({
-              owner: context.repo.owner,
-              repo: context.repo.repo,
-              tag_name: `cmd/cigocacher/${{ github.sha }}`,
-              name: `cigocacher-${{ github.sha }}`,
-              draft: false,
-              prerelease: true,
-              target_commitish: `${{ github.sha }}`
-            });
-
-            const files = fs.readdirSync('.').filter(f => f.endsWith('.tar.gz'));
-            
-            for (const file of files) {
-              await github.rest.repos.uploadReleaseAsset({
-                owner: context.repo.owner,
-                repo: context.repo.repo,
-                release_id: release.id,
-                name: file,
-                data: fs.readFileSync(file)
-              });
-              console.log(`Uploaded ${file}`);
-            }
diff --git a/.github/workflows/codeql-analysis.yml b/.github/workflows/codeql-analysis.yml
deleted file mode 100644
index 51bae5a068df5..0000000000000
--- a/.github/workflows/codeql-analysis.yml
+++ /dev/null
@@ -1,83 +0,0 @@
-# For most projects, this workflow file will not need changing; you simply need
-# to commit it to your repository.
-#
-# You may wish to alter this file to override the set of languages analyzed,
-# or to provide custom queries or build logic.
-#
-# ******** NOTE ********
-# We have attempted to detect the languages in your repository. Please check
-# the `language` matrix defined below to confirm you have the correct set of
-# supported CodeQL languages.
-#
-name: "CodeQL"
-
-on:
-  push:
-    branches: [ main, release-branch/* ]
-  pull_request:
-    # The branches below must be a subset of the branches above
-    branches: [ main ]
-  merge_group:
-    branches: [ main ]
-  schedule:
-    - cron: '31 14 * * 5'
-
-concurrency:
-  group: ${{ github.workflow }}-${{ github.head_ref || github.run_id }}
-  cancel-in-progress: true
-
-jobs:
-  analyze:
-    name: Analyze
-    runs-on: ubuntu-latest
-    permissions:
-      actions: read
-      contents: read
-      security-events: write
-
-    strategy:
-      fail-fast: false
-      matrix:
-        language: [ 'go' ]
-        # CodeQL supports [ 'cpp', 'csharp', 'go', 'java', 'javascript', 'python' ]
-        # Learn more:
-        # https://docs.github.com/en/free-pro-team@latest/github/finding-security-vulnerabilities-and-errors-in-your-code/configuring-code-scanning#changing-the-languages-that-are-analyzed
-
-    steps:
-    - name: Checkout repository
-      uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
-
-    # Install a more recent Go that understands modern go.mod content.
-    - name: Install Go
-      uses: actions/setup-go@4b73464bb391d4059bd26b0524d20df3927bd417 # v6.3.0
-      with:
-        go-version-file: go.mod
-
-    # Initializes the CodeQL tools for scanning.
-    - name: Initialize CodeQL
-      uses: github/codeql-action/init@c793b717bc78562f491db7b0e93a3a178b099162 # v4.32.5
-      with:
-        languages: ${{ matrix.language }}
-        # If you wish to specify custom queries, you can do so here or in a config file.
-        # By default, queries listed here will override any specified in a config file.
-        # Prefix the list here with "+" to use these queries and those in the config file.
-        # queries: ./path/to/local/query, your-org/your-repo/queries@main
-
-    # Autobuild attempts to build any compiled languages  (C/C++, C#, or Java).
-    # If this step fails, then you should remove it and run the build manually (see below)
-    - name: Autobuild
-      uses: github/codeql-action/autobuild@c793b717bc78562f491db7b0e93a3a178b099162 # v4.32.5
-
-    # ℹ️ Command-line programs to run using the OS shell.
-    # 📚 https://git.io/JvXDl
-
-    # ✏️ If the Autobuild fails above, remove it and uncomment the following three lines
-    #    and modify them (or add more) to build your code if your project
-    #    uses a compiled language
-
-    #- run: |
-    #   make bootstrap
-    #   make release
-
-    - name: Perform CodeQL Analysis
-      uses: github/codeql-action/analyze@c793b717bc78562f491db7b0e93a3a178b099162 # v4.32.5
diff --git a/.github/workflows/docker-base.yml b/.github/workflows/docker-base.yml
deleted file mode 100644
index a3eac2c24e691..0000000000000
--- a/.github/workflows/docker-base.yml
+++ /dev/null
@@ -1,29 +0,0 @@
-name: "Validate Docker base image"
-on: 
-  workflow_dispatch:
-  pull_request:
-    paths:
-    - "Dockerfile.base"
-    - ".github/workflows/docker-base.yml"
-jobs:
-  build-and-test:
-    runs-on: ubuntu-latest
-    steps:
-    - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
-    - name: "build and test"
-      run: |
-        set -e
-        IMG="test-base:$(head -c 8 /dev/urandom | xxd -p)"
-        docker build -t "$IMG" -f Dockerfile.base .
-
-        iptables_version=$(docker run --rm "$IMG" iptables --version)
-        if [[ "$iptables_version" != *"(legacy)"* ]]; then
-            echo "ERROR: Docker base image should contain legacy iptables; found ${iptables_version}"
-            exit 1
-        fi
-
-        ip6tables_version=$(docker run --rm "$IMG" ip6tables --version)
-        if [[ "$ip6tables_version" != *"(legacy)"* ]]; then
-            echo "ERROR: Docker base image should contain legacy ip6tables; found ${ip6tables_version}"
-            exit 1
-        fi
diff --git a/.github/workflows/docker-file-build.yml b/.github/workflows/docker-file-build.yml
deleted file mode 100644
index 7ee2468682695..0000000000000
--- a/.github/workflows/docker-file-build.yml
+++ /dev/null
@@ -1,13 +0,0 @@
-name: "Dockerfile build"
-on: 
-  push:
-    branches:
-    - main
-  pull_request:
-jobs:
-  deploy:
-    runs-on: ubuntu-latest
-    steps:
-    - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
-    - name: "Build Docker image"
-      run: docker build .
diff --git a/.github/workflows/flakehub-publish-tagged.yml b/.github/workflows/flakehub-publish-tagged.yml
deleted file mode 100644
index c781e30e5154f..0000000000000
--- a/.github/workflows/flakehub-publish-tagged.yml
+++ /dev/null
@@ -1,27 +0,0 @@
-name: update-flakehub
-
-on:
-  push:
-    tags:
-      - "v[0-9]+.*[02468].[0-9]+"
-  workflow_dispatch:
-    inputs:
-      tag:
-        description: "The existing tag to publish to FlakeHub"
-        type: "string"
-        required: true
-jobs:
-  flakehub-publish:
-    runs-on: "ubuntu-latest"
-    permissions:
-      id-token: "write"
-      contents: "read"
-    steps:
-      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
-        with:
-          ref: "${{ (inputs.tag != null) && format('refs/tags/{0}', inputs.tag) || '' }}"
-      - uses: DeterminateSystems/nix-installer-action@c5a866b6ab867e88becbed4467b93592bce69f8a # v21
-      - uses: DeterminateSystems/flakehub-push@71f57208810a5d299fc6545350981de98fdbc860 # v6
-        with:
-          visibility: "public"
-          tag: "${{ inputs.tag }}"
diff --git a/.github/workflows/golangci-lint.yml b/.github/workflows/golangci-lint.yml
deleted file mode 100644
index 66b8497e65441..0000000000000
--- a/.github/workflows/golangci-lint.yml
+++ /dev/null
@@ -1,47 +0,0 @@
-name: golangci-lint
-on:
-  # For now, only lint pull requests, not the main branches.
-  pull_request:
-    paths:
-      - ".github/workflows/golangci-lint.yml"
-      - "**.go"
-      - "go.mod"
-      - "go.sum"
-  # TODO(andrew): enable for main branch after an initial waiting period.
-  #push:
-  #  branches:
-  #    - main
-
-  workflow_dispatch:
-
-permissions:
-  contents: read
-  pull-requests: read
-
-concurrency:
-  group: ${{ github.workflow }}-${{ github.head_ref || github.run_id }}
-  cancel-in-progress: true
-
-jobs:
-  golangci:
-    name: lint
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
-
-      - uses: actions/setup-go@4b73464bb391d4059bd26b0524d20df3927bd417 # v6.3.0
-        with:
-          go-version-file: go.mod
-          cache: true
-
-      - name: golangci-lint
-        uses: golangci/golangci-lint-action@b7bcab6379029e905e3f389a6bf301f1bc220662 # head as of 2026-03-04
-        with:
-          version: v2.10.1
-
-          # Show only new issues if it's a pull request.
-          only-new-issues: true
-
-          # Loading packages with a cold cache takes a while:
-          args: --timeout=10m
-          
diff --git a/.github/workflows/govulncheck.yml b/.github/workflows/govulncheck.yml
deleted file mode 100644
index 2b46aa9b06e57..0000000000000
--- a/.github/workflows/govulncheck.yml
+++ /dev/null
@@ -1,51 +0,0 @@
-name: govulncheck
-
-on:
-  schedule:
-    - cron: "0 12 * * *" # 8am EST / 10am PST / 12pm UTC
-  workflow_dispatch: # allow manual trigger for testing
-  pull_request:
-    paths:
-      - ".github/workflows/govulncheck.yml"
-
-jobs:
-  source-scan:
-    runs-on: ubuntu-latest
-
-    steps:
-      - name: Check out code into the Go module directory
-        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
-
-      - name: Install govulncheck
-        run: ./tool/go install golang.org/x/vuln/cmd/govulncheck@latest
-
-      - name: Scan source code for known vulnerabilities
-        run: PATH=$PWD/tool/:$PATH "$(./tool/go env GOPATH)/bin/govulncheck" -test ./...
-
-      - name: Post to slack
-        if: failure() && github.event_name == 'schedule'
-        uses: slackapi/slack-github-action@91efab103c0de0a537f72a35f6b8cda0ee76bf0a # v2.1.1
-        with:
-          method: chat.postMessage
-          token: ${{ secrets.GOVULNCHECK_BOT_TOKEN }}
-          payload: |
-            {
-              "channel": "C08FGKZCQTW",
-              "blocks": [
-                {
-                  "type": "section",
-                  "text": {
-                    "type": "mrkdwn",
-                    "text": "Govulncheck failed in ${{ github.repository }}"
-                  },
-                  "accessory": {
-                    "type": "button",
-                    "text": {
-                      "type": "plain_text",
-                      "text": "View results"
-                    },
-                    "url": "${{ github.server_url }}/${{ github.repository }}/actions/runs/${{ github.run_id }}"
-                  }
-                }
-              ]
-            }
diff --git a/.github/workflows/installer.yml b/.github/workflows/installer.yml
deleted file mode 100644
index 6fc8913c4e19c..0000000000000
--- a/.github/workflows/installer.yml
+++ /dev/null
@@ -1,143 +0,0 @@
-name: test installer.sh
-
-on:
-  schedule:
-    - cron: '0 15 * * *' # 10am EST (UTC-4/5)
-  push:
-    branches:
-      - "main"
-    paths:
-      - scripts/installer.sh
-      - .github/workflows/installer.yml
-  pull_request:
-    paths:
-      - scripts/installer.sh
-      - .github/workflows/installer.yml
-
-jobs:
-  test:
-    strategy:
-      # Don't abort the entire matrix if one element fails.
-      fail-fast: false
-      # Don't start all of these at once, which could saturate Github workers.
-      max-parallel: 4
-      matrix:
-        image:
-          # This is a list of Docker images against which we test our installer.
-          # If you find that some of these no longer exist, please feel free
-          # to remove them from the list.
-          # When adding new images, please only use official ones.
-          - "debian:oldstable-slim"
-          - "debian:stable-slim"
-          - "debian:testing-slim"
-          - "debian:sid-slim"
-          - "ubuntu:20.04"
-          - "ubuntu:22.04"
-          - "ubuntu:24.04"
-          - "elementary/docker:stable"
-          - "elementary/docker:unstable"
-          - "parrotsec/core:latest"
-          - "kalilinux/kali-rolling"
-          - "kalilinux/kali-dev"
-          - "oraclelinux:9"
-          - "oraclelinux:8"
-          - "fedora:latest"
-          - "rockylinux:8.7"
-          - "rockylinux:9"
-          - "amazonlinux:latest"
-          - "opensuse/leap:latest"
-          - "opensuse/tumbleweed:latest"
-          - "archlinux:latest"
-          - "alpine:3.21"
-          - "alpine:latest"
-          - "alpine:edge"
-        deps:
-          # Run all images installing curl as a dependency.
-          - curl
-        include:
-          # Check a few images with wget rather than curl.
-          - { image: "debian:oldstable-slim", deps: "wget" }
-          - { image: "debian:sid-slim", deps: "wget" }
-          - { image: "debian:stable-slim", deps: "curl" }
-          - { image: "ubuntu:24.04", deps: "curl" }
-          - { image: "fedora:latest", deps: "curl" }
-          # Test TAILSCALE_VERSION pinning on a subset of distros.
-          # Skip Alpine as community repos don't reliably keep old versions.
-          - { image: "debian:stable-slim", deps: "curl", version: "1.80.0" }
-          - { image: "ubuntu:24.04", deps: "curl", version: "1.80.0" }
-          - { image: "fedora:latest", deps: "curl", version: "1.80.0" }
-    runs-on: ubuntu-latest
-    container:
-      image: ${{ matrix.image }}
-      options: --user root
-    steps:
-    - name: install dependencies (pacman)
-      # Refresh the package databases to ensure that the tailscale package is
-      # defined.
-      run: pacman -Sy
-      if: contains(matrix.image, 'archlinux')
-    - name: install dependencies (yum)
-      # tar and gzip are needed by the actions/checkout below.
-      run: yum install -y --allowerasing tar gzip ${{ matrix.deps }}
-      if: |
-        contains(matrix.image, 'centos') ||
-        contains(matrix.image, 'oraclelinux') ||
-        contains(matrix.image, 'fedora') ||
-        contains(matrix.image, 'amazonlinux')
-    - name: install dependencies (zypper)
-      # tar and gzip are needed by the actions/checkout below.
-      run: zypper --non-interactive install tar gzip ${{ matrix.deps }}
-      if: contains(matrix.image, 'opensuse')
-    - name: install dependencies (apt-get)
-      run: |
-        apt-get update
-        apt-get install -y ${{ matrix.deps }}
-      if: |
-        contains(matrix.image, 'debian') ||
-        contains(matrix.image, 'ubuntu') ||
-        contains(matrix.image, 'elementary') ||
-        contains(matrix.image, 'parrotsec') ||
-        contains(matrix.image, 'kalilinux')
-    - name: checkout
-      uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
-    - name: run installer
-      run: scripts/installer.sh
-      env:
-        TAILSCALE_VERSION: ${{ matrix.version }}
-      # Package installation can fail in docker because systemd is not running
-      # as PID 1, so ignore errors at this step. The real check is the
-      # `tailscale --version` command below.
-      continue-on-error: true
-    - name: check tailscale version
-      run: |
-        tailscale --version
-        if [ -n "${{ matrix.version }}" ]; then
-          tailscale --version | grep -q "^${{ matrix.version }}" || { echo "Version mismatch!"; exit 1; }
-        fi
-  notify-slack:
-    needs: test
-    runs-on: ubuntu-latest
-    steps:
-      - name: Notify Slack of failure on scheduled runs
-        if: failure() && github.event_name == 'schedule'
-        uses: slackapi/slack-github-action@91efab103c0de0a537f72a35f6b8cda0ee76bf0a # v2.1.1
-        with:
-          webhook: ${{ secrets.SLACK_WEBHOOK_URL }}
-          webhook-type: incoming-webhook
-          payload: |
-            {
-              "attachments": [{
-                "title": "Tailscale installer test failed",
-                "title_link": "https://github.com/${{ github.repository }}/actions/runs/${{ github.run_id }}",
-                "text": "One or more OSes in the test matrix failed. See the run for details.",
-                "fields": [
-                  {
-                    "title": "Ref",
-                    "value": "${{ github.ref_name }}",
-                    "short": true
-                  }
-                ],
-                "footer": "${{ github.workflow }} on schedule",
-                "color": "danger"
-              }]
-            }
diff --git a/.github/workflows/kubemanifests.yaml b/.github/workflows/kubemanifests.yaml
deleted file mode 100644
index 40734a015dad3..0000000000000
--- a/.github/workflows/kubemanifests.yaml
+++ /dev/null
@@ -1,31 +0,0 @@
-name: "Kubernetes manifests"
-on:
-  pull_request:
-   paths: 
-   - 'cmd/k8s-operator/**'
-   - 'k8s-operator/**'
-   - '.github/workflows/kubemanifests.yaml'
-
-# Cancel workflow run if there is a newer push to the same PR for which it is
-# running
-concurrency:
-  group: ${{ github.workflow }}-${{ github.head_ref || github.run_id }}
-  cancel-in-progress: true
-
-jobs:
-  testchart:
-    runs-on: [ ubuntu-latest ]
-    steps:
-    - name: Check out code
-      uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
-    - name: Build and lint Helm chart
-      run: |
-        eval `./tool/go run ./cmd/mkversion`
-        ./tool/helm package --app-version="${VERSION_SHORT}" --version=${VERSION_SHORT} './cmd/k8s-operator/deploy/chart'
-        ./tool/helm lint "tailscale-operator-${VERSION_SHORT}.tgz"
-    - name: Verify that static manifests are up to date
-      run: |
-        make kube-generate-all
-        echo
-        echo
-        git diff --name-only --exit-code || (echo "Generated files for Tailscale Kubernetes operator are out of date. Please run 'make kube-generate-all' and commit the diff."; exit 1)
diff --git a/.github/workflows/natlab-integrationtest.yml b/.github/workflows/natlab-integrationtest.yml
deleted file mode 100644
index 162153cb23293..0000000000000
--- a/.github/workflows/natlab-integrationtest.yml
+++ /dev/null
@@ -1,33 +0,0 @@
-# Run some natlab integration tests.
-# See https://github.com/tailscale/tailscale/issues/13038
-name: "natlab-integrationtest"
-
-concurrency:
-  group: ${{ github.workflow }}-${{ github.head_ref || github.run_id }}
-  cancel-in-progress: true
-
-on:
-  push:
-    branches:
-      - "main"
-      - "release-branch/*"
-  pull_request:
-    # all PRs on all branches
-  merge_group:
-    branches:
-      - "main"
-jobs:
-  natlab-integrationtest:
-    runs-on: ubuntu-latest
-    steps:
-      - name: Check out code
-        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
-      - name: Install qemu
-        run: |
-          sudo rm -f /var/lib/man-db/auto-update
-          sudo apt-get -y update
-          sudo apt-get -y remove man-db
-          sudo apt-get install -y qemu-system-x86 qemu-utils
-      - name: Run natlab integration tests
-        run: |
-          ./tool/go test -v -run=^TestEasyEasy$ -timeout=3m -count=1 ./tstest/integration/nat  --run-vm-tests
diff --git a/.github/workflows/pin-github-actions.yml b/.github/workflows/pin-github-actions.yml
deleted file mode 100644
index 836ae46dbfa89..0000000000000
--- a/.github/workflows/pin-github-actions.yml
+++ /dev/null
@@ -1,29 +0,0 @@
-# Pin images used in github actions to a hash instead of a version tag.
-name: pin-github-actions
-on:
-  pull_request:
-    branches:
-      - main
-    paths:
-      - ".github/workflows/**"
-
-  workflow_dispatch:
-
-permissions:
-  contents: read
-  pull-requests: read
-
-concurrency:
-  group: ${{ github.workflow }}-${{ github.head_ref || github.run_id }}
-  cancel-in-progress: true
-
-jobs:
-  run:
-    name: pin-github-actions
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
-      - name: pin
-        run: make pin-github-actions
-      - name: check for changed workflow files
-        run: git diff --no-ext-diff --exit-code .github/workflows || (echo "Some github actions versions need pinning, run make pin-github-actions."; exit 1)
diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
new file mode 100644
index 0000000000000..e20003c16b13e
--- /dev/null
+++ b/.github/workflows/release.yml
@@ -0,0 +1,117 @@
+name: Release
+on:
+  push:
+    tags: ['v*-scion.*']
+
+jobs:
+  build-linux:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        goarch: [amd64, arm64]
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-go@v5
+        with:
+          go-version-file: go.mod
+      - name: Verify version
+        run: |
+          eval $(go run ./cmd/mkversion)
+          echo "Version: $VERSION_LONG"
+      - name: Build packages
+        run: |
+          go run ./cmd/dist build \
+            "linux/${{ matrix.goarch }}/tgz" \
+            "linux/${{ matrix.goarch }}/deb" \
+            "linux/${{ matrix.goarch }}/rpm"
+      - uses: actions/upload-artifact@v4
+        with:
+          name: linux-${{ matrix.goarch }}
+          path: dist/
+
+  build-macos:
+    runs-on: macos-latest
+    strategy:
+      matrix:
+        goarch: [amd64, arm64]
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-go@v5
+        with:
+          go-version-file: go.mod
+      - name: Build binaries
+        env:
+          GOOS: darwin
+          GOARCH: ${{ matrix.goarch }}
+          CGO_ENABLED: 0
+        run: |
+          eval $(go run ./cmd/mkversion)
+          mkdir -p dist
+          ./build_dist.sh -o dist/tailscale ./cmd/tailscale
+          ./build_dist.sh -o dist/tailscaled ./cmd/tailscaled
+          cp LICENSE PATENTS NOTICE dist/ 2>/dev/null || true
+          tar czf "dist/tailscale-scion_${VERSION_SHORT}_macos_${{ matrix.goarch }}.tgz" \
+            -C dist tailscale tailscaled LICENSE PATENTS NOTICE
+      - uses: actions/upload-artifact@v4
+        with:
+          name: macos-${{ matrix.goarch }}
+          path: dist/*.tgz
+
+  build-windows:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-go@v5
+        with:
+          go-version-file: go.mod
+      - name: Build binaries
+        env:
+          GOOS: windows
+          GOARCH: amd64
+          CGO_ENABLED: 0
+        run: |
+          eval $(go run ./cmd/mkversion)
+          mkdir -p dist
+          ./build_dist.sh -o dist/tailscale.exe ./cmd/tailscale
+          ./build_dist.sh -o dist/tailscaled.exe ./cmd/tailscaled
+          cp LICENSE PATENTS NOTICE dist/ 2>/dev/null || true
+          cd dist && zip "tailscale-scion_${VERSION_SHORT}_windows_amd64.zip" \
+            tailscale.exe tailscaled.exe LICENSE PATENTS NOTICE
+      - uses: actions/upload-artifact@v4
+        with:
+          name: windows-amd64
+          path: dist/*.zip
+
+  release:
+    needs: [build-linux, build-macos, build-windows]
+    runs-on: ubuntu-latest
+    permissions:
+      contents: write
+    steps:
+      - uses: actions/download-artifact@v4
+        with:
+          merge-multiple: true
+          path: artifacts
+      - name: Create GitHub Release
+        uses: softprops/action-gh-release@v2
+        with:
+          files: artifacts/**/*
+          generate_release_notes: true
+          body: |
+            ## Tailscale (SCION) ${{ github.ref_name }}
+
+            Unofficial Tailscale client with SCION path-aware networking.
+            Based on Tailscale. Not affiliated with Tailscale Inc.
+
+            ### Install
+
+            **Linux (deb):** `sudo dpkg -i tailscale-scion_*.deb && sudo systemctl enable --now tailscaled`
+            **Linux (rpm):** `sudo rpm -i tailscale-scion_*.rpm && sudo systemctl enable --now tailscaled`
+            **Linux (tgz):** Extract and copy `tailscale`/`tailscaled` to PATH
+            **macOS:** Extract tgz, run `sudo ./tailscaled &` then `./tailscale up`
+            **Windows:** Extract zip, run `tailscaled.exe` then `tailscale.exe up`
+
+            ### Documentation
+
+            CLI reference: https://tailscale.com/docs/reference/tailscale-cli
+            SCION configuration: https://github.com/netsys-lab/tailscale-scion#configuration
\ No newline at end of file
diff --git a/.github/workflows/request-dataplane-review.yml b/.github/workflows/request-dataplane-review.yml
deleted file mode 100644
index 2b66fc7899428..0000000000000
--- a/.github/workflows/request-dataplane-review.yml
+++ /dev/null
@@ -1,32 +0,0 @@
-name: request-dataplane-review
-
-on:
-  pull_request:
-    types: [ opened, synchronize, reopened, ready_for_review ]
-    paths:
-      - ".github/workflows/request-dataplane-review.yml"
-      - "**/*derp*"
-      - "**/derp*/**"
-      - "!**/depaware.txt"
-
-jobs:
-  request-dataplane-review:
-    if: github.event.pull_request.draft == false
-    name: Request Dataplane Review
-    runs-on: ubuntu-latest
-    steps:
-      - name: Check out code
-        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
-      - name: Get access token
-        uses: actions/create-github-app-token@29824e69f54612133e76f7eaac726eef6c875baf # v2.2.1
-        id: generate-token
-        with:
-          # Get token for app: https://github.com/apps/change-visibility-bot
-          app-id: ${{ secrets.VISIBILITY_BOT_APP_ID }}
-          private-key: ${{ secrets.VISIBILITY_BOT_APP_PRIVATE_KEY }}
-      - name: Add reviewers
-        env:
-          GH_TOKEN: ${{ steps.generate-token.outputs.token }}
-          url: ${{ github.event.pull_request.html_url }}
-        run: |
-          gh pr edit "$url" --add-reviewer tailscale/dataplane
diff --git a/.github/workflows/ssh-integrationtest.yml b/.github/workflows/ssh-integrationtest.yml
deleted file mode 100644
index afe2dd2f74683..0000000000000
--- a/.github/workflows/ssh-integrationtest.yml
+++ /dev/null
@@ -1,23 +0,0 @@
-# Run the ssh integration tests with `make sshintegrationtest`.
-# These tests can also be running locally.
-name: "ssh-integrationtest"
-
-concurrency:
-  group: ${{ github.workflow }}-${{ github.head_ref || github.run_id }}
-  cancel-in-progress: true
-
-on:
-  pull_request:
-    paths:
-      - "ssh/**"
-      - "tempfork/gliderlabs/ssh/**"
-      - ".github/workflows/ssh-integrationtest"
-jobs:
-  ssh-integrationtest:
-    runs-on: ubuntu-latest
-    steps:
-      - name: Check out code
-        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
-      - name: Run SSH integration tests
-        run: |
-          make sshintegrationtest
\ No newline at end of file
diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
deleted file mode 100644
index 4f6068e6e33cd..0000000000000
--- a/.github/workflows/test.yml
+++ /dev/null
@@ -1,1007 +0,0 @@
-# This is our main "CI tests" workflow. It runs everything that should run on
-# both PRs and merged commits, and for the latter reports failures to slack.
-name: CI
-
-env:
-  # Our fuzz job, powered by OSS-Fuzz, fails periodically because we upgrade to
-  # new Go versions very eagerly. OSS-Fuzz is a little more conservative, and
-  # ends up being unable to compile our code.
-  #
-  # When this happens, we want to disable the fuzz target until OSS-Fuzz catches
-  # up. However, we also don't want to forget to turn it back on when OSS-Fuzz
-  # can once again build our code.
-  #
-  # This variable toggles the fuzz job between two modes:
-  #  - false: we expect fuzzing to be happy, and should report failure if it's not.
-  #  - true: we expect fuzzing is broken, and should report failure if it start working.
-  TS_FUZZ_CURRENTLY_BROKEN: false
-  # GOMODCACHE is the same definition on all OSes. Within the workspace, we use
-  # toplevel directories "src" (for the checked out source code), and "gomodcache"
-  # and other caches as siblings to follow.
-  GOMODCACHE: ${{ github.workspace }}/gomodcache
-  CMD_GO_USE_GIT_HASH: "true"
-
-on:
-  push:
-    branches:
-      - "main"
-      - "release-branch/*"
-  pull_request:
-    # all PRs on all branches
-  merge_group:
-    branches:
-      - "main"
-
-concurrency:
-  # For PRs, later CI runs preempt previous ones. e.g. a force push on a PR
-  # cancels running CI jobs and starts all new ones.
-  #
-  # For non-PR pushes, concurrency.group needs to be unique for every distinct
-  # CI run we want to have happen. Use run_id, which in practice means all
-  # non-PR CI runs will be allowed to run without preempting each other.
-  group: ${{ github.workflow }}-$${{ github.pull_request.number || github.run_id }}
-  cancel-in-progress: true
-
-jobs:
-  gomod-cache:
-    runs-on: ubuntu-24.04
-    outputs:
-      cache-key: ${{ steps.hash.outputs.key }}
-    steps:
-      - name: Checkout
-        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
-        with:
-          path: src
-      - name: Compute cache key from go.{mod,sum}
-        id: hash
-        run: echo "key=gomod-cross3-${{ hashFiles('src/go.mod', 'src/go.sum') }}" >> $GITHUB_OUTPUT
-      # See if the cache entry already exists to avoid downloading it
-      # and doing the cache write again.
-      - id: check-cache
-        uses: actions/cache/restore@cdf6c1fa76f9f475f3d7449005a359c84ca0f306 # v5.0.3
-        with:
-          path: gomodcache # relative to workspace; see env note at top of file
-          key: ${{ steps.hash.outputs.key }}
-          lookup-only: true
-          enableCrossOsArchive: true
-      - name: Download modules
-        if: steps.check-cache.outputs.cache-hit != 'true'
-        working-directory: src
-        run: go mod download
-      - name: Cache Go modules
-        if: steps.check-cache.outputs.cache-hit != 'true'
-        uses: actions/cache@cdf6c1fa76f9f475f3d7449005a359c84ca0f306 # v5.0.3
-        with:
-          path: gomodcache # relative to workspace; see env note at top of file
-          key: ${{ steps.hash.outputs.key }}
-          enableCrossOsArchive: true
-
-  race-root-integration:
-    runs-on: ubuntu-24.04
-    needs: gomod-cache
-    strategy:
-      fail-fast: false # don't abort the entire matrix if one element fails
-      matrix:
-        include:
-          - shard: '1/4'
-          - shard: '2/4'
-          - shard: '3/4'
-          - shard: '4/4'
-    steps:
-    - name: checkout
-      uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
-      with:
-        path: src
-    - name: Restore Go module cache
-      uses: actions/cache/restore@cdf6c1fa76f9f475f3d7449005a359c84ca0f306 # v5.0.3
-      with:
-        path: gomodcache
-        key: ${{ needs.gomod-cache.outputs.cache-key }}
-        enableCrossOsArchive: true
-    - name: build test wrapper
-      working-directory: src
-      run: ./tool/go build -o /tmp/testwrapper ./cmd/testwrapper
-    - name: integration tests as root
-      working-directory: src
-      run: PATH=$PWD/tool:$PATH /tmp/testwrapper -exec "sudo -E" -race ./tstest/integration/
-      env:
-        TS_TEST_SHARD: ${{ matrix.shard }}
-
-  test:
-    strategy:
-      fail-fast: false # don't abort the entire matrix if one element fails
-      matrix:
-        include:
-          - goarch: amd64
-          - goarch: amd64
-            buildflags: "-race"
-            shard: '1/3'
-          - goarch: amd64
-            buildflags: "-race"
-            shard: '2/3'
-          - goarch: amd64
-            buildflags: "-race"
-            shard: '3/3'
-          - goarch: "386" # thanks yaml
-    runs-on: ubuntu-24.04
-    needs: gomod-cache
-    steps:
-    - name: checkout
-      uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
-      with:
-        path: src
-    - name: Restore Go module cache
-      uses: actions/cache/restore@cdf6c1fa76f9f475f3d7449005a359c84ca0f306 # v5.0.3
-      with:
-        path: gomodcache
-        key: ${{ needs.gomod-cache.outputs.cache-key }}
-        enableCrossOsArchive: true
-    - name: Restore Cache
-      id: restore-cache
-      uses: actions/cache/restore@cdf6c1fa76f9f475f3d7449005a359c84ca0f306 # v5.0.3
-      with:
-        # Note: this is only restoring the build cache. Mod cache is shared amongst
-        # all jobs in the workflow.
-        path: |
-          ~/.cache/go-build
-          ~\AppData\Local\go-build
-        key: ${{ runner.os }}-${{ matrix.goarch }}-${{ matrix.buildflags }}-go-${{ matrix.shard }}-${{ hashFiles('**/go.sum') }}-${{ github.job }}-${{ github.run_id }}
-        restore-keys: |
-          ${{ runner.os }}-${{ matrix.goarch }}-${{ matrix.buildflags }}-go-${{ matrix.shard }}-${{ hashFiles('**/go.sum') }}-${{ github.job }}-
-          ${{ runner.os }}-${{ matrix.goarch }}-${{ matrix.buildflags }}-go-${{ matrix.shard }}-${{ hashFiles('**/go.sum') }}-
-          ${{ runner.os }}-${{ matrix.goarch }}-${{ matrix.buildflags }}-go-${{ matrix.shard }}-
-          ${{ runner.os }}-${{ matrix.goarch }}-${{ matrix.buildflags }}-go-
-    - name: build all
-      if: matrix.buildflags == '' # skip on race builder
-      working-directory: src
-      run: ./tool/go build ${{matrix.buildflags}} ./...
-      env:
-        GOARCH: ${{ matrix.goarch }}
-    - name: build variant CLIs
-      if: matrix.buildflags == '' # skip on race builder
-      working-directory: src
-      run: |
-        ./build_dist.sh --extra-small ./cmd/tailscaled
-        ./build_dist.sh --box ./cmd/tailscaled
-        ./build_dist.sh --extra-small --box ./cmd/tailscaled
-        rm -f tailscaled
-      env:
-        GOARCH: ${{ matrix.goarch }}
-    - name: get qemu # for tstest/archtest
-      if: matrix.goarch == 'amd64' && matrix.buildflags == ''
-      run: |
-        sudo apt-get -y update
-        sudo apt-get -y install qemu-user
-    - name: build test wrapper
-      working-directory: src
-      run: ./tool/go build -o /tmp/testwrapper ./cmd/testwrapper
-    - name: test all
-      working-directory: src
-      run: NOBASHDEBUG=true NOPWSHDEBUG=true PATH=$PWD/tool:$PATH /tmp/testwrapper ./... ${{matrix.buildflags}}
-      env:
-        GOARCH: ${{ matrix.goarch }}
-        TS_TEST_SHARD: ${{ matrix.shard }}
-    - name: bench all
-      working-directory: src
-      run: ./tool/go test ${{matrix.buildflags}} -bench=. -benchtime=1x -run=^$ $(for x in $(git grep -l "^func Benchmark" | xargs dirname | sort | uniq); do echo "./$x"; done)
-      env:
-        GOARCH: ${{ matrix.goarch }}
-    - name: check that no tracked files changed
-      working-directory: src
-      run: git diff --no-ext-diff --name-only --exit-code || (echo "Build/test modified the files above."; exit 1)
-    - name: check that no new files were added
-      working-directory: src
-      run: |
-        # Note: The "error: pathspec..." you see below is normal!
-        # In the success case in which there are no new untracked files,
-        # git ls-files complains about the pathspec not matching anything.
-        # That's OK. It's not worth the effort to suppress. Please ignore it.
-        if git ls-files --others --exclude-standard --directory --no-empty-directory --error-unmatch -- ':/*'
-        then
-          echo "Build/test created untracked files in the repo (file names above)."
-          exit 1
-        fi
-    - name: Tidy cache
-      working-directory: src
-      shell: bash
-      run: |
-        find $(go env GOCACHE) -type f -mmin +90 -delete
-    - name: Save Cache
-      # Save cache even on failure, but only on cache miss and main branch to avoid thrashing.
-      if: always() && steps.restore-cache.outputs.cache-hit != 'true' && github.ref == 'refs/heads/main'
-      uses: actions/cache/save@cdf6c1fa76f9f475f3d7449005a359c84ca0f306 # v5.0.3
-      with:
-        # Note: this is only saving the build cache. Mod cache is shared amongst
-        # all jobs in the workflow.
-        path: |
-          ~/.cache/go-build
-          ~\AppData\Local\go-build
-        key: ${{ runner.os }}-${{ matrix.goarch }}-${{ matrix.buildflags }}-go-${{ matrix.shard }}-${{ hashFiles('**/go.sum') }}-${{ github.job }}-${{ github.run_id }}
-
-  windows:
-    permissions:
-      id-token: write # This is required for requesting the GitHub action identity JWT that can auth to cigocached
-      contents: read # This is required for actions/checkout
-    # ci-windows-github-1 is a 2022 GitHub-managed runner in our org with 8 cores
-    # and 32 GB of RAM. It is connected to a private Azure VNet that hosts cigocached.
-    # https://github.com/organizations/tailscale/settings/actions/github-hosted-runners/5
-    runs-on: ci-windows-github-1
-    needs: gomod-cache
-    name: Windows (${{ matrix.name || matrix.shard}})
-    strategy:
-      fail-fast: false # don't abort the entire matrix if one element fails
-      matrix:
-        include:
-          - key: "win-bench"
-            name: "benchmarks"
-          - key: "win-shard-1-2"
-            shard: "1/2"
-          - key: "win-shard-2-2"
-            shard: "2/2"
-    steps:
-    - name: checkout
-      uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
-      with:
-        path: ${{ github.workspace }}/src
-
-    - name: Restore Go module cache
-      uses: actions/cache/restore@cdf6c1fa76f9f475f3d7449005a359c84ca0f306 # v5.0.3
-      with:
-        path: gomodcache
-        key: ${{ needs.gomod-cache.outputs.cache-key }}
-        enableCrossOsArchive: true
-
-    - name: Set up cigocacher
-      id: cigocacher-setup
-      uses: ./src/.github/actions/go-cache
-      with:
-        checkout-path: ${{ github.workspace }}/src
-        cache-dir: ${{ github.workspace }}/cigocacher
-        cigocached-url: ${{ vars.CIGOCACHED_AZURE_URL }}
-        cigocached-host: ${{ vars.CIGOCACHED_AZURE_HOST }}
-
-    - name: test
-      if: matrix.key != 'win-bench' # skip on bench builder
-      working-directory: src
-      run: ./tool/go run ./cmd/testwrapper sharded:${{ matrix.shard }}
-      env:
-        NOPWSHDEBUG: "true" # to quiet tool/gocross/gocross-wrapper.ps1 in CI
-
-    - name: bench all
-      if: matrix.key == 'win-bench'
-      working-directory: src
-      # Don't use -bench=. -benchtime=1x.
-      # Somewhere in the layers (powershell?)
-      # the equals signs cause great confusion.
-      run: ./tool/go test ./... -bench . -benchtime 1x -run "^$"
-      env:
-        NOPWSHDEBUG: "true" # to quiet tool/gocross/gocross-wrapper.ps1 in CI
-
-    - name: Print stats
-      shell: pwsh
-      if: steps.cigocacher-setup.outputs.success == 'true'
-      env:
-        GOCACHEPROG: ${{ env.GOCACHEPROG }}
-      run: |
-        Invoke-Expression "$env:GOCACHEPROG --stats" | jq .
-
-  macos:
-    runs-on: macos-latest
-    needs: gomod-cache
-    steps:
-    - name: checkout
-      uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
-      with:
-        path: src
-    - name: Restore Go module cache
-      uses: actions/cache/restore@cdf6c1fa76f9f475f3d7449005a359c84ca0f306 # v5.0.3
-      with:
-        path: gomodcache
-        key: ${{ needs.gomod-cache.outputs.cache-key }}
-        enableCrossOsArchive: true
-    - name: Restore Cache
-      id: restore-cache
-      uses: actions/cache/restore@cdf6c1fa76f9f475f3d7449005a359c84ca0f306 # v5.0.3
-      with:
-        path: ~/Library/Caches/go-build
-        key: ${{ runner.os }}-go-test-${{ hashFiles('**/go.sum') }}-${{ github.job }}-${{ github.run_id }}
-        restore-keys: |
-          ${{ runner.os }}-go-test-${{ hashFiles('**/go.sum') }}-${{ github.job }}-
-          ${{ runner.os }}-go-test-${{ hashFiles('**/go.sum') }}-
-          ${{ runner.os }}-go-test-
-    - name: build test wrapper
-      working-directory: src
-      run: ./tool/go build -o /tmp/testwrapper ./cmd/testwrapper
-    - name: test all
-      working-directory: src
-      run: PATH=$PWD/tool:$PATH /tmp/testwrapper ./...
-    - name: check that no tracked files changed
-      working-directory: src
-      run: git diff --no-ext-diff --name-only --exit-code || (echo "Build/test modified the files above."; exit 1)
-    - name: check that no new files were added
-      working-directory: src
-      run: |
-        # Note: The "error: pathspec..." you see below is normal!
-        # In the success case in which there are no new untracked files,
-        # git ls-files complains about the pathspec not matching anything.
-        # That's OK. It's not worth the effort to suppress. Please ignore it.
-        if git ls-files --others --exclude-standard --directory --no-empty-directory --error-unmatch -- ':/*'
-        then
-          echo "Build/test created untracked files in the repo (file names above)."
-          exit 1
-        fi
-    - name: Tidy cache
-      working-directory: src
-      run: |
-        find $(./tool/go env GOCACHE) -type f -mmin +90 -delete
-    - name: Save Cache
-      # Save cache even on failure, but only on cache miss and main branch to avoid thrashing.
-      if: always() && steps.restore-cache.outputs.cache-hit != 'true' && github.ref == 'refs/heads/main'
-      uses: actions/cache/save@cdf6c1fa76f9f475f3d7449005a359c84ca0f306 # v5.0.3
-      with:
-        path: ~/Library/Caches/go-build
-        key: ${{ runner.os }}-go-test-${{ hashFiles('**/go.sum') }}-${{ github.job }}-${{ github.run_id }}
-
-  privileged:
-    needs: gomod-cache
-    runs-on: ubuntu-24.04
-    container:
-      image: golang:latest
-      options: --privileged
-    steps:
-    - name: checkout
-      uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
-      with:
-        path: src
-    - name: Restore Go module cache
-      uses: actions/cache/restore@cdf6c1fa76f9f475f3d7449005a359c84ca0f306 # v5.0.3
-      with:
-        path: gomodcache
-        key: ${{ needs.gomod-cache.outputs.cache-key }}
-        enableCrossOsArchive: true
-    - name: chown
-      working-directory: src
-      run: chown -R $(id -u):$(id -g) $PWD
-    - name: privileged tests
-      working-directory: src
-      run: ./tool/go test ./util/linuxfw ./derp/xdp
-
-  vm:
-    needs: gomod-cache
-    runs-on: ["self-hosted", "linux", "vm"]
-    # VM tests run with some privileges, don't let them run on 3p PRs.
-    if: github.repository == 'tailscale/tailscale'
-    steps:
-    - name: checkout
-      uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
-      with:
-        path: src
-    - name: Restore Go module cache
-      uses: actions/cache/restore@cdf6c1fa76f9f475f3d7449005a359c84ca0f306 # v5.0.3
-      with:
-        path: gomodcache
-        key: ${{ needs.gomod-cache.outputs.cache-key }}
-        enableCrossOsArchive: true
-    - name: Run VM tests
-      working-directory: src
-      run: ./tool/go test ./tstest/integration/vms -v -no-s3 -run-vm-tests -run=TestRunUbuntu2404
-      env:
-        HOME: "/var/lib/ghrunner/home"
-        TMPDIR: "/tmp"
-        XDG_CACHE_HOME: "/var/lib/ghrunner/cache"
-
-  cross: # cross-compile checks, build only.
-    needs: gomod-cache
-    strategy:
-      fail-fast: false # don't abort the entire matrix if one element fails
-      matrix:
-        include:
-          # Note: linux/amd64 is not in this matrix, because that goos/goarch is
-          # tested more exhaustively in the 'test' job above.
-          - goos: linux
-            goarch: arm64
-          - goos: linux
-            goarch: "386" # thanks yaml
-          - goos: linux
-            goarch: loong64
-          - goos: linux
-            goarch: arm
-            goarm: "5"
-          - goos: linux
-            goarch: arm
-            goarm: "7"
-          # macOS
-          - goos: darwin
-            goarch: amd64
-          - goos: darwin
-            goarch: arm64
-          # Windows
-          - goos: windows
-            goarch: amd64
-          - goos: windows
-            goarch: arm64
-          # BSDs
-          - goos: freebsd
-            goarch: amd64
-          - goos: openbsd
-            goarch: amd64
-
-    runs-on: ubuntu-24.04
-    steps:
-    - name: checkout
-      uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
-      with:
-        path: src
-    - name: Restore Go module cache
-      uses: actions/cache/restore@cdf6c1fa76f9f475f3d7449005a359c84ca0f306 # v5.0.3
-      with:
-        path: gomodcache
-        key: ${{ needs.gomod-cache.outputs.cache-key }}
-        enableCrossOsArchive: true
-    - name: Restore Cache
-      id: restore-cache
-      uses: actions/cache/restore@cdf6c1fa76f9f475f3d7449005a359c84ca0f306 # v5.0.3
-      with:
-        # Note: this is only restoring the build cache. Mod cache is shared amongst
-        # all jobs in the workflow.
-        path: |
-          ~/.cache/go-build
-          ~\AppData\Local\go-build
-        key: ${{ runner.os }}-${{ matrix.goos }}-${{ matrix.goarch }}-${{ matrix.goarm }}-go-${{ hashFiles('**/go.sum') }}-${{ github.job }}-${{ github.run_id }}
-        restore-keys: |
-          ${{ runner.os }}-${{ matrix.goos }}-${{ matrix.goarch }}-${{ matrix.goarm }}-go-${{ hashFiles('**/go.sum') }}-${{ github.job }}-
-          ${{ runner.os }}-${{ matrix.goos }}-${{ matrix.goarch }}-${{ matrix.goarm }}-go-${{ hashFiles('**/go.sum') }}-
-          ${{ runner.os }}-${{ matrix.goos }}-${{ matrix.goarch }}-${{ matrix.goarm }}-go-
-    - name: build all
-      working-directory: src
-      run: ./tool/go build ./cmd/...
-      env:
-        GOOS: ${{ matrix.goos }}
-        GOARCH: ${{ matrix.goarch }}
-        GOARM: ${{ matrix.goarm }}
-        CGO_ENABLED: "0"
-    - name: build tests
-      working-directory: src
-      run: ./tool/go test -exec=true ./...
-      env:
-        GOOS: ${{ matrix.goos }}
-        GOARCH: ${{ matrix.goarch }}
-        CGO_ENABLED: "0"
-    - name: Tidy cache
-      working-directory: src
-      shell: bash
-      run: |
-        find $(go env GOCACHE) -type f -mmin +90 -delete
-    - name: Save Cache
-      # Save cache even on failure, but only on cache miss and main branch to avoid thrashing.
-      if: always() && steps.restore-cache.outputs.cache-hit != 'true' && github.ref == 'refs/heads/main'
-      uses: actions/cache/save@cdf6c1fa76f9f475f3d7449005a359c84ca0f306 # v5.0.3
-      with:
-        # Note: this is only saving the build cache. Mod cache is shared amongst
-        # all jobs in the workflow.
-        path: |
-          ~/.cache/go-build
-          ~\AppData\Local\go-build
-        key: ${{ runner.os }}-${{ matrix.goos }}-${{ matrix.goarch }}-${{ matrix.goarm }}-go-${{ hashFiles('**/go.sum') }}-${{ github.job }}-${{ github.run_id }}
-
-  ios: # similar to cross above, but iOS can't build most of the repo. So, just
-       # make it build a few smoke packages.
-    runs-on: ubuntu-24.04
-    needs: gomod-cache
-    steps:
-    - name: checkout
-      uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
-      with:
-        path: src
-    - name: Restore Go module cache
-      uses: actions/cache/restore@cdf6c1fa76f9f475f3d7449005a359c84ca0f306 # v5.0.3
-      with:
-        path: gomodcache
-        key: ${{ needs.gomod-cache.outputs.cache-key }}
-        enableCrossOsArchive: true
-    - name: build some
-      working-directory: src
-      run: ./tool/go build ./ipn/... ./ssh/tailssh ./wgengine/ ./types/... ./control/controlclient
-      env:
-        GOOS: ios
-        GOARCH: arm64
-
-  crossmin: # cross-compile for platforms where we only check cmd/tailscale{,d}
-    needs: gomod-cache
-    strategy:
-      fail-fast: false # don't abort the entire matrix if one element fails
-      matrix:
-        include:
-          # Plan9
-          - goos: plan9
-            goarch: amd64
-          # AIX
-          - goos: aix
-            goarch: ppc64
-          # Solaris
-          - goos: solaris
-            goarch: amd64
-          # illumos
-          - goos: illumos
-            goarch: amd64
-
-    runs-on: ubuntu-24.04
-    steps:
-    - name: checkout
-      uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
-      with:
-        path: src
-    - name: Restore Go module cache
-      uses: actions/cache/restore@cdf6c1fa76f9f475f3d7449005a359c84ca0f306 # v5.0.3
-      with:
-        path: gomodcache
-        key: ${{ needs.gomod-cache.outputs.cache-key }}
-        enableCrossOsArchive: true
-    - name: Restore Cache
-      id: restore-cache
-      uses: actions/cache/restore@cdf6c1fa76f9f475f3d7449005a359c84ca0f306 # v5.0.3
-      with:
-        # Note: this is only restoring the build cache. Mod cache is shared amongst
-        # all jobs in the workflow.
-        path: |
-          ~/.cache/go-build
-          ~\AppData\Local\go-build
-        key: ${{ runner.os }}-${{ matrix.goos }}-${{ matrix.goarch }}-go-${{ hashFiles('**/go.sum') }}-${{ github.job }}-${{ github.run_id }}
-        restore-keys: |
-          ${{ runner.os }}-${{ matrix.goos }}-${{ matrix.goarch }}-go-${{ hashFiles('**/go.sum') }}-${{ github.job }}-
-          ${{ runner.os }}-${{ matrix.goos }}-${{ matrix.goarch }}-go-${{ hashFiles('**/go.sum') }}-
-          ${{ runner.os }}-${{ matrix.goos }}-${{ matrix.goarch }}-go-
-    - name: build core
-      working-directory: src
-      run: ./tool/go build ./cmd/tailscale ./cmd/tailscaled
-      env:
-        GOOS: ${{ matrix.goos }}
-        GOARCH: ${{ matrix.goarch }}
-        GOARM: ${{ matrix.goarm }}
-        CGO_ENABLED: "0"
-    - name: Tidy cache
-      working-directory: src
-      shell: bash
-      run: |
-        find $(go env GOCACHE) -type f -mmin +90 -delete
-    - name: Save Cache
-      # Save cache even on failure, but only on cache miss and main branch to avoid thrashing.
-      if: always() && steps.restore-cache.outputs.cache-hit != 'true' && github.ref == 'refs/heads/main'
-      uses: actions/cache/save@cdf6c1fa76f9f475f3d7449005a359c84ca0f306 # v5.0.3
-      with:
-        # Note: this is only saving the build cache. Mod cache is shared amongst
-        # all jobs in the workflow.
-        path: |
-          ~/.cache/go-build
-          ~\AppData\Local\go-build
-        key: ${{ runner.os }}-${{ matrix.goos }}-${{ matrix.goarch }}-go-${{ hashFiles('**/go.sum') }}-${{ github.job }}-${{ github.run_id }}
-
-  android:
-    # similar to cross above, but android fails to build a few pieces of the
-    # repo. We should fix those pieces, they're small, but as a stepping stone,
-    # only test the subset of android that our past smoke test checked.
-    runs-on: ubuntu-24.04
-    needs: gomod-cache
-    steps:
-    - name: checkout
-      uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
-      with:
-        path: src
-      # Super minimal Android build that doesn't even use CGO and doesn't build everything that's needed
-      # and is only arm64. But it's a smoke build: it's not meant to catch everything. But it'll catch
-      # some Android breakages early.
-      # TODO(bradfitz): better; see https://github.com/tailscale/tailscale/issues/4482
-    - name: Restore Go module cache
-      uses: actions/cache/restore@cdf6c1fa76f9f475f3d7449005a359c84ca0f306 # v5.0.3
-      with:
-        path: gomodcache
-        key: ${{ needs.gomod-cache.outputs.cache-key }}
-        enableCrossOsArchive: true
-    - name: build some
-      working-directory: src
-      run: ./tool/go install ./net/netns ./ipn/ipnlocal ./wgengine/magicsock/ ./wgengine/ ./wgengine/router/ ./wgengine/netstack ./util/dnsname/ ./ipn/ ./net/netmon ./wgengine/router/ ./tailcfg/ ./types/logger/ ./net/dns ./hostinfo ./version ./ssh/tailssh
-      env:
-        GOOS: android
-        GOARCH: arm64
-
-  wasm: # builds tsconnect, which is the only wasm build we support
-    runs-on: ubuntu-24.04
-    needs: gomod-cache
-    steps:
-    - name: checkout
-      uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
-      with:
-        path: src
-    - name: Restore Go module cache
-      uses: actions/cache/restore@cdf6c1fa76f9f475f3d7449005a359c84ca0f306 # v5.0.3
-      with:
-        path: gomodcache
-        key: ${{ needs.gomod-cache.outputs.cache-key }}
-        enableCrossOsArchive: true
-    - name: Restore Cache
-      id: restore-cache
-      uses: actions/cache/restore@cdf6c1fa76f9f475f3d7449005a359c84ca0f306 # v5.0.3
-      with:
-        # Note: this is only restoring the build cache. Mod cache is shared amongst
-        # all jobs in the workflow.
-        path: |
-          ~/.cache/go-build
-          ~\AppData\Local\go-build
-        key: ${{ runner.os }}-js-wasm-go-${{ hashFiles('**/go.sum') }}-${{ github.job }}-${{ github.run_id }}
-        restore-keys: |
-          ${{ runner.os }}-js-wasm-go-${{ hashFiles('**/go.sum') }}-${{ github.job }}-
-          ${{ runner.os }}-js-wasm-go-${{ hashFiles('**/go.sum') }}-
-          ${{ runner.os }}-js-wasm-go-
-    - name: build tsconnect client
-      working-directory: src
-      run: ./tool/go build ./cmd/tsconnect/wasm ./cmd/tailscale/cli
-      env:
-        GOOS: js
-        GOARCH: wasm
-    - name: build tsconnect server
-      working-directory: src
-      # Note, no GOOS/GOARCH in env on this build step, we're running a build
-      # tool that handles the build itself.
-      run: |
-        ./tool/go run ./cmd/tsconnect --fast-compression build
-        ./tool/go run ./cmd/tsconnect --fast-compression build-pkg
-    - name: Tidy cache
-      working-directory: src
-      shell: bash
-      run: |
-        find $(go env GOCACHE) -type f -mmin +90 -delete
-    - name: Save Cache
-      # Save cache even on failure, but only on cache miss and main branch to avoid thrashing.
-      if: always() && steps.restore-cache.outputs.cache-hit != 'true' && github.ref == 'refs/heads/main'
-      uses: actions/cache/save@cdf6c1fa76f9f475f3d7449005a359c84ca0f306 # v5.0.3
-      with:
-        # Note: this is only saving the build cache. Mod cache is shared amongst
-        # all jobs in the workflow.
-        path: |
-          ~/.cache/go-build
-          ~\AppData\Local\go-build
-        key: ${{ runner.os }}-js-wasm-go-${{ hashFiles('**/go.sum') }}-${{ github.job }}-${{ github.run_id }}
-
-  tailscale_go: # Subset of tests that depend on our custom Go toolchain.
-    runs-on: ubuntu-24.04
-    needs: gomod-cache
-    steps:
-    - name: checkout
-      uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
-    - name: Set GOMODCACHE env
-      run: echo "GOMODCACHE=$HOME/.cache/go-mod" >> $GITHUB_ENV
-    - name: Restore Go module cache
-      uses: actions/cache/restore@cdf6c1fa76f9f475f3d7449005a359c84ca0f306 # v5.0.3
-      with:
-        path: gomodcache
-        key: ${{ needs.gomod-cache.outputs.cache-key }}
-        enableCrossOsArchive: true
-    - name: test tailscale_go
-      run: ./tool/go test -tags=tailscale_go,ts_enable_sockstats ./net/sockstats/...
-
-
-  fuzz:
-    # This target periodically breaks (see TS_FUZZ_CURRENTLY_BROKEN at the top
-    # of the file), so it's more complex than usual: the 'build fuzzers' step
-    # might fail, and depending on the value of 'TS_FUZZ_CURRENTLY_BROKEN', that
-    # might or might not be fine. The steps after the build figure out whether
-    # the success/failure is expected, and appropriately pass/fail the job
-    # overall accordingly.
-    #
-    # Practically, this means that all steps after 'build fuzzers' must have an
-    # explicit 'if' condition, because the default condition for steps is
-    # 'success()', meaning "only run this if no previous steps failed".
-    if: github.event_name == 'pull_request'
-    runs-on: ubuntu-24.04
-    steps:
-    - name: build fuzzers
-      id: build
-      # As of 12 February 2026, this repo doesn't tag releases, so this commit
-      # hash is just the tip of master.
-      uses: google/oss-fuzz/infra/cifuzz/actions/build_fuzzers@f277aafb36f358582fdb24a41a9a52f2e097a2fd
-      # continue-on-error makes steps.build.conclusion be 'success' even if
-      # steps.build.outcome is 'failure'. This means this step does not
-      # contribute to the job's overall pass/fail evaluation.
-      continue-on-error: true
-      with:
-       oss-fuzz-project-name: 'tailscale'
-       dry-run: false
-       language: go
-    - name: report unexpectedly broken fuzz build
-      if: steps.build.outcome == 'failure' && env.TS_FUZZ_CURRENTLY_BROKEN != 'true'
-      run: |
-        echo "fuzzer build failed, see above for why"
-        echo "if the failure is due to OSS-Fuzz not being on the latest Go yet,"
-        echo "set TS_FUZZ_CURRENTLY_BROKEN=true in .github/workflows/test.yml"
-        echo "to temporarily disable fuzzing until OSS-Fuzz works again."
-        exit 1
-    - name: report unexpectedly working fuzz build
-      if: steps.build.outcome == 'success' && env.TS_FUZZ_CURRENTLY_BROKEN == 'true'
-      run: |
-        echo "fuzzer build succeeded, but we expect it to be broken"
-        echo "please set TS_FUZZ_CURRENTLY_BROKEN=false in .github/workflows/test.yml"
-        echo "to reenable fuzz testing"
-        exit 1
-    - name: run fuzzers
-      id: run
-      # Run the fuzzers whenever they're able to build, even if we're going to
-      # report a failure because TS_FUZZ_CURRENTLY_BROKEN is set to the wrong
-      # value.
-      if: steps.build.outcome == 'success'
-      # As of 12 February 2026, this repo doesn't tag releases, so this commit
-      # hash is just the tip of master.
-      uses: google/oss-fuzz/infra/cifuzz/actions/run_fuzzers@f277aafb36f358582fdb24a41a9a52f2e097a2fd
-      with:
-        oss-fuzz-project-name: 'tailscale'
-        fuzz-seconds: 150
-        dry-run: false
-        language: go
-    - name: Set artifacts_path in env (workaround for actions/upload-artifact#176)
-      if: steps.run.outcome != 'success' && steps.build.outcome == 'success'
-      run: |
-        echo "artifacts_path=$(realpath .)" >> $GITHUB_ENV
-    - name: upload crash
-      uses: actions/upload-artifact@b7c566a772e6b6bfb58ed0dc250532a479d7789f # v6.0.0
-      if: steps.run.outcome != 'success' && steps.build.outcome == 'success'
-      with:
-        name: artifacts
-        path: ${{ env.artifacts_path }}/out/artifacts
-
-  depaware:
-    runs-on: ubuntu-24.04
-    needs: gomod-cache
-    steps:
-    - name: checkout
-      uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
-      with:
-        path: src
-    - name: Set GOMODCACHE env
-      run: echo "GOMODCACHE=$HOME/.cache/go-mod" >> $GITHUB_ENV
-    - name: Restore Go module cache
-      uses: actions/cache/restore@cdf6c1fa76f9f475f3d7449005a359c84ca0f306 # v5.0.3
-      with:
-        path: gomodcache
-        key: ${{ needs.gomod-cache.outputs.cache-key }}
-        enableCrossOsArchive: true
-    - name: check depaware
-      working-directory: src
-      run: make depaware
-
-  go_generate:
-    runs-on: ubuntu-24.04
-    needs: gomod-cache
-    steps:
-    - name: checkout
-      uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
-      with:
-        path: src
-    - name: Restore Go module cache
-      uses: actions/cache/restore@cdf6c1fa76f9f475f3d7449005a359c84ca0f306 # v5.0.3
-      with:
-        path: gomodcache
-        key: ${{ needs.gomod-cache.outputs.cache-key }}
-        enableCrossOsArchive: true
-    - name: check that 'go generate' is clean
-      working-directory: src
-      run: |
-        pkgs=$(./tool/go list ./... | grep -Ev 'dnsfallback|k8s-operator|xdp')
-        ./tool/go generate $pkgs
-        git add -N . # ensure untracked files are noticed
-        echo
-        echo
-        git diff --name-only --exit-code || (echo "The files above need updating. Please run 'go generate'."; exit 1)
-
-  make_tidy:
-    runs-on: ubuntu-24.04
-    needs: gomod-cache
-    steps:
-    - name: checkout
-      uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
-      with:
-        path: src
-    - name: Restore Go module cache
-      uses: actions/cache/restore@cdf6c1fa76f9f475f3d7449005a359c84ca0f306 # v5.0.3
-      with:
-        path: gomodcache
-        key: ${{ needs.gomod-cache.outputs.cache-key }}
-        enableCrossOsArchive: true
-    - name: check that 'make tidy' is clean
-      working-directory: src
-      run: |
-        make tidy
-        echo
-        echo
-        git diff --name-only --exit-code || (echo "Please run 'make tidy'"; exit 1)
-
-  licenses:
-    runs-on: ubuntu-24.04
-    needs: gomod-cache
-    steps:
-    - name: checkout
-      uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
-      with:
-        path: src
-    - name: Restore Go module cache
-      uses: actions/cache/restore@cdf6c1fa76f9f475f3d7449005a359c84ca0f306 # v5.0.3
-      with:
-        path: gomodcache
-        key: ${{ needs.gomod-cache.outputs.cache-key }}
-        enableCrossOsArchive: true
-    - name: check licenses
-      working-directory: src
-      run: |
-        grep -q TestLicenseHeaders *.go || (echo "Expected a test named TestLicenseHeaders"; exit 1)
-        ./tool/go test -v -run=TestLicenseHeaders
-
-  staticcheck:
-    runs-on: ubuntu-24.04
-    needs: gomod-cache
-    name: staticcheck (${{ matrix.name }})
-    strategy:
-      fail-fast: false # don't abort the entire matrix if one element fails
-      matrix:
-        include:
-          - name: "macOS"
-            goos: "darwin"
-            goarch: "arm64"
-            flags: "--with-tags-all=darwin"
-          - name: "Windows"
-            goos: "windows"
-            goarch: "amd64"
-            flags: "--with-tags-all=windows"
-          - name: "Linux"
-            goos: "linux"
-            goarch: "amd64"
-            flags: "--with-tags-all=linux"
-          - name: "Portable (1/4)"
-            goos: "linux"
-            goarch: "amd64"
-            flags: "--without-tags-any=windows,darwin,linux --shard=1/4"
-          - name: "Portable (2/4)"
-            goos: "linux"
-            goarch: "amd64"
-            flags: "--without-tags-any=windows,darwin,linux --shard=2/4"
-          - name: "Portable (3/4)"
-            goos: "linux"
-            goarch: "amd64"
-            flags: "--without-tags-any=windows,darwin,linux --shard=3/4"
-          - name: "Portable (4/4)"
-            goos: "linux"
-            goarch: "amd64"
-            flags: "--without-tags-any=windows,darwin,linux --shard=4/4"
-
-    steps:
-    - name: checkout
-      uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
-      with:
-        path: src
-    - name: Restore Go module cache
-      uses: actions/cache/restore@cdf6c1fa76f9f475f3d7449005a359c84ca0f306 # v5.0.3
-      with:
-        path: gomodcache
-        key: ${{ needs.gomod-cache.outputs.cache-key }}
-        enableCrossOsArchive: true
-    - name: run staticcheck (${{ matrix.name }})
-      working-directory: src
-      run: |
-        export GOROOT=$(./tool/go env GOROOT)
-        ./tool/go run -exec \
-          "env GOOS=${{ matrix.goos }} GOARCH=${{ matrix.goarch }}" \
-           honnef.co/go/tools/cmd/staticcheck -- \
-           $(./tool/go run ./tool/listpkgs --ignore-3p --goos=${{ matrix.goos }} --goarch=${{ matrix.goarch }} ${{ matrix.flags }} ./...)
-
-  notify_slack:
-    if: always()
-    # Any of these jobs failing causes a slack notification.
-    needs:
-      - android
-      - test
-      - windows
-      - macos
-      - vm
-      - cross
-      - ios
-      - wasm
-      - tailscale_go
-      - fuzz
-      - depaware
-      - go_generate
-      - make_tidy
-      - licenses
-      - staticcheck
-    runs-on: ubuntu-24.04
-    steps:
-    - name: notify  
-      # Only notify slack for merged commits, not PR failures.
-      #
-      # It may be tempting to move this condition into the job's 'if' block, but
-      # don't: Github only collapses the test list into "everything is OK" if
-      # all jobs succeeded. A skipped job results in the list staying expanded.
-      # By having the job always run, but skipping its only step as needed, we
-      # let the CI output collapse nicely in PRs.
-      if: failure() && github.event_name == 'push'
-      uses: slackapi/slack-github-action@91efab103c0de0a537f72a35f6b8cda0ee76bf0a # v2.1.1
-      with:
-        webhook: ${{ secrets.SLACK_WEBHOOK_URL }}
-        webhook-type: incoming-webhook
-        payload: |
-          {
-            "attachments": [{
-              "title": "Failure: ${{ github.workflow }}",
-              "title_link": "https://github.com/${{ github.repository }}/commit/${{ github.sha }}/checks",         
-              "text": "${{ github.repository }}@${{ github.ref_name }}: <https://github.com/${{ github.repository }}/commit/${{ github.sha }}|${{ github.sha }}>",
-              "fields": [{ "value": ${{ toJson(github.event.head_commit.message) }}, "short": false }],
-              "footer": "${{ github.event.head_commit.committer.name }} at ${{ github.event.head_commit.timestamp }}",
-              "color": "danger"
-            }]
-          }
-
-  merge_blocker:
-    if: always()
-    runs-on: ubuntu-24.04
-    needs:
-      - android
-      - test
-      - windows
-      - macos
-      - vm
-      - cross
-      - ios
-      - wasm
-      - tailscale_go
-      - fuzz
-      - depaware
-      - go_generate
-      - make_tidy
-      - licenses
-      - staticcheck
-    steps:
-    - name: Decide if change is okay to merge
-      if: github.event_name != 'push'
-      uses: re-actors/alls-green@05ac9388f0aebcb5727afa17fcccfecd6f8ec5fe # v1.2.2
-      with:
-        jobs: ${{ toJSON(needs) }}
-
-   # This waits on all the jobs which must never fail. Branch protection rules
-   # enforce these. No flaky tests are allowed in these jobs. (We don't want flaky
-   # tests anywhere, really, but a flaky test here prevents merging.)
-  check_mergeability_strict:
-    if: always()
-    runs-on: ubuntu-24.04
-    needs:
-      - android
-      - cross
-      - crossmin
-      - ios
-      - tailscale_go
-      - depaware
-      - go_generate
-      - make_tidy
-      - licenses
-      - staticcheck
-    steps:
-    - name: Decide if change is okay to merge
-      if: github.event_name != 'push'
-      uses: re-actors/alls-green@05ac9388f0aebcb5727afa17fcccfecd6f8ec5fe # v1.2.2
-      with:
-        jobs: ${{ toJSON(needs) }}
-
-  check_mergeability:
-    if: always()
-    runs-on: ubuntu-24.04
-    needs:
-      - check_mergeability_strict
-      - test
-      - windows
-      - macos
-      - vm
-      - wasm
-      - fuzz
-      - race-root-integration
-      - privileged
-    steps:
-    - name: Decide if change is okay to merge
-      if: github.event_name != 'push'
-      uses: re-actors/alls-green@05ac9388f0aebcb5727afa17fcccfecd6f8ec5fe # v1.2.2
-      with:
-        jobs: ${{ toJSON(needs) }}
diff --git a/.github/workflows/update-flake.yml b/.github/workflows/update-flake.yml
deleted file mode 100644
index 4c0da7831b5ba..0000000000000
--- a/.github/workflows/update-flake.yml
+++ /dev/null
@@ -1,49 +0,0 @@
-name: update-flake
-
-on:
-  # run action when a change lands in the main branch which updates go.mod. Also
-  # allow manual triggering.
-  push:
-    branches:
-      - main
-    paths:
-      - go.mod
-      - .github/workflows/update-flake.yml
-  workflow_dispatch:
-
-concurrency:
-  group: ${{ github.workflow }}-${{ github.head_ref || github.run_id }}
-  cancel-in-progress: true
-
-jobs:
-  update-flake:
-    runs-on: ubuntu-latest
-
-    steps:
-      - name: Check out code
-        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
-
-      - name: Run update-flakes
-        run: ./update-flake.sh
-
-      - name: Get access token
-        uses: actions/create-github-app-token@29824e69f54612133e76f7eaac726eef6c875baf # v2.2.1
-        id: generate-token
-        with:
-          # Get token for app: https://github.com/apps/tailscale-code-updater
-          app-id: ${{ secrets.CODE_UPDATER_APP_ID }}
-          private-key: ${{ secrets.CODE_UPDATER_APP_PRIVATE_KEY }}
-
-      - name: Send pull request
-        uses: peter-evans/create-pull-request@c0f553fe549906ede9cf27b5156039d195d2ece0 #v8.1.0
-        with:
-          token: ${{ steps.generate-token.outputs.token }}
-          author: Flakes Updater <noreply+flakes-updater@tailscale.com>
-          committer: Flakes Updater <noreply+flakes-updater@tailscale.com>
-          branch: flakes
-          commit-message: "go.mod.sri: update SRI hash for go.mod changes"
-          title: "go.mod.sri: update SRI hash for go.mod changes"
-          body: Triggered by ${{ github.repository }}@${{ github.sha }}
-          signoff: true
-          delete-branch: true
-          reviewers: danderson
diff --git a/.github/workflows/update-webclient-prebuilt.yml b/.github/workflows/update-webclient-prebuilt.yml
deleted file mode 100644
index a3d78e1a5b4a8..0000000000000
--- a/.github/workflows/update-webclient-prebuilt.yml
+++ /dev/null
@@ -1,50 +0,0 @@
-name: update-webclient-prebuilt
-
-on:
-  # manually triggered
-  workflow_dispatch:
-
-concurrency:
-  group: ${{ github.workflow }}-${{ github.head_ref || github.run_id }}
-  cancel-in-progress: true
-
-jobs:
-  update-webclient-prebuilt:
-    runs-on: ubuntu-latest
-
-    steps:
-      - name: Check out code
-        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
-
-      - name: Run go get
-        run: |
-          ./tool/go version # build gocross if needed using regular GOPROXY
-          GOPROXY=direct ./tool/go get github.com/tailscale/web-client-prebuilt
-          ./tool/go mod tidy
-
-      - name: Get access token
-        uses: actions/create-github-app-token@29824e69f54612133e76f7eaac726eef6c875baf # v2.2.1
-        id: generate-token
-        with:
-          # Get token for app: https://github.com/apps/tailscale-code-updater
-          app-id: ${{ secrets.CODE_UPDATER_APP_ID }}
-          private-key: ${{ secrets.CODE_UPDATER_APP_PRIVATE_KEY }}
-
-      - name: Send pull request
-        id: pull-request
-        uses: peter-evans/create-pull-request@c0f553fe549906ede9cf27b5156039d195d2ece0 #v8.1.0
-        with:
-          token: ${{ steps.generate-token.outputs.token }}
-          author: OSS Updater <noreply+oss-updater@tailscale.com>
-          committer: OSS Updater <noreply+oss-updater@tailscale.com>
-          branch: actions/update-webclient-prebuilt
-          commit-message: "go.mod: update web-client-prebuilt module"
-          title: "go.mod: update web-client-prebuilt module"
-          body: Triggered by ${{ github.repository }}@${{ github.sha }}
-          signoff: true
-          delete-branch: true
-          reviewers: ${{ github.triggering_actor }}
-
-      - name: Summary
-        if: ${{ steps.pull-request.outputs.pull-request-number }}
-        run: echo "${{ steps.pull-request.outputs.pull-request-operation}} ${{ steps.pull-request.outputs.pull-request-url }}" >> $GITHUB_STEP_SUMMARY
diff --git a/.github/workflows/vet.yml b/.github/workflows/vet.yml
deleted file mode 100644
index 574852e62beee..0000000000000
--- a/.github/workflows/vet.yml
+++ /dev/null
@@ -1,39 +0,0 @@
-name: tailscale.com/cmd/vet
-
-env:
-  HOME: ${{ github.workspace }}
-  # GOMODCACHE is the same definition on all OSes. Within the workspace, we use
-  # toplevel directories "src" (for the checked out source code), and "gomodcache"
-  # and other caches as siblings to follow.
-  GOMODCACHE: ${{ github.workspace }}/gomodcache
-  CMD_GO_USE_GIT_HASH: "true"
-
-on:
-  push:
-    branches:
-      - main
-      - "release-branch/*"
-    paths:
-      - "**.go"
-  pull_request:
-    paths:
-      - "**.go"
-
-jobs:
-  vet:
-    runs-on: [ self-hosted, linux ]
-    timeout-minutes: 5
-
-    steps:
-      - name: Check out code
-        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
-        with:
-          path: src
-
-      - name: Build 'go vet' tool
-        working-directory: src
-        run: ./tool/go build -o /tmp/vettool tailscale.com/cmd/vet
-
-      - name: Run 'go vet'
-        working-directory: src
-        run: ./tool/go vet -vettool=/tmp/vettool tailscale.com/...
diff --git a/.github/workflows/webclient.yml b/.github/workflows/webclient.yml
deleted file mode 100644
index 1a65eacf56414..0000000000000
--- a/.github/workflows/webclient.yml
+++ /dev/null
@@ -1,38 +0,0 @@
-name: webclient
-on:
-  workflow_dispatch:
-  # For now, only run on requests, not the main branches.
-  pull_request:
-    paths:
-      - "client/web/**"
-      - ".github/workflows/webclient.yml"
-      - "!**.md"
-  # TODO(soniaappasamy): enable for main branch after an initial waiting period.
-  #push:
-  #  branches:
-  #    - main
-
-concurrency:
-  group: ${{ github.workflow }}-${{ github.head_ref || github.run_id }}
-  cancel-in-progress: true
-
-jobs:
-  webclient:
-    runs-on: ubuntu-latest
-
-    steps:
-      - name: Check out code
-        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
-      - name: Install deps
-        run: ./tool/yarn --cwd client/web
-      - name: Run lint
-        run: ./tool/yarn --cwd client/web run --silent lint
-      - name: Run test
-        run: ./tool/yarn --cwd client/web run --silent test
-      - name: Run formatter check
-        run: |
-          ./tool/yarn --cwd client/web run --silent format-check || ( \
-            echo "Run this command on your local device to fix the error:" && \
-            echo "" && \
-            echo "  ./tool/yarn --cwd client/web format" && \
-            echo "" && exit 1)
diff --git a/NOTICE b/NOTICE
new file mode 100644
index 0000000000000..7250122885807
--- /dev/null
+++ b/NOTICE
@@ -0,0 +1,11 @@
+Tailscale (SCION) - Unofficial Tailscale client with SCION path-aware networking
+
+Based on Tailscale (https://github.com/tailscale/tailscale)
+Copyright (c) 2020 Tailscale Inc & contributors. Licensed under BSD-3-Clause.
+
+SCION networking provided by scionproto/scion
+(https://github.com/scionproto/scion), licensed under Apache-2.0.
+
+Tailscale is a registered trademark of Tailscale Inc.
+This project is not affiliated with or endorsed by Tailscale Inc.
+WireGuard is a registered trademark of Jason A. Donenfeld.
\ No newline at end of file
diff --git a/README.md b/README.md
index 70b92d411b9de..0a50b3ed3f21c 100644
--- a/README.md
+++ b/README.md
@@ -1,87 +1,107 @@
-# Tailscale
+# Tailscale (SCION)
 
-https://tailscale.com
+Tailscale fork with SCION path-aware transport.
 
-Private WireGuard® networks made easy
+## What This Is
 
-## Overview
+A fork of [tailscale/tailscale](https://github.com/tailscale/tailscale) that adds [SCION](https://www.scion.org/) as a transport layer alongside WireGuard's existing UDP. Peers on SCION-enabled ASes gets path-aware routing with latency-based path selection.
 
-This repository contains the majority of Tailscale's open source code.
-Notably, it includes the `tailscaled` daemon and
-the `tailscale` CLI tool. The `tailscaled` daemon runs on Linux, Windows,
-[macOS](https://tailscale.com/kb/1065/macos-variants/), and to varying degrees
-on FreeBSD and OpenBSD. The Tailscale iOS and Android apps use this repo's
-code, but this repo doesn't contain the mobile GUI code.
+> **This project is not affiliated with or endorsed by Tailscale Inc.**
 
-Other [Tailscale repos](https://github.com/orgs/tailscale/repositories) of note:
+## Status
 
-* the Android app is at https://github.com/tailscale/tailscale-android
-* the Synology package is at https://github.com/tailscale/tailscale-synology
-* the QNAP package is at https://github.com/tailscale/tailscale-qpkg
-* the Chocolatey packaging is at https://github.com/tailscale/tailscale-chocolatey
+Experimental. Platforms: Linux, macOS, Windows, FreeBSD, OpenBSD, NetBSD, Android (via [tailscale-android-scion](https://github.com/netsys-lab/tailscale-android-scion)).
 
-For background on which parts of Tailscale are open source and why,
-see [https://tailscale.com/opensource/](https://tailscale.com/opensource/).
+## Releases
 
-## Using
+Pre-built binaries for Linux (amd64/arm64), macOS, and Windows are available on the [Releases](https://github.com/netsys-lab/tailscale-scion/releases) page. Android APK releases are available from [tailscale-android-scion](https://github.com/netsys-lab/tailscale-android-scion/releases).
 
-We serve packages for a variety of distros and platforms at
-[https://pkgs.tailscale.com](https://pkgs.tailscale.com/).
+For CLI usage, see the [Tailscale CLI reference](https://tailscale.com/docs/reference/tailscale-cli) — all standard `tailscale` and `tailscaled` commands work the same.
 
-## Other clients
+## Quick Start (Linux)
 
-The [macOS, iOS, and Windows clients](https://tailscale.com/download)
-use the code in this repository but additionally include small GUI
-wrappers. The GUI wrappers on non-open source platforms are themselves
-not open source.
-
-## Building
+```bash
+# Build
+go install tailscale.com/cmd/tailscale{,d}
 
-We always require the latest Go release, currently Go 1.25. (While we build
-releases with our [Go fork](https://github.com/tailscale/go/), its use is not
-required.)
+# Run with embedded SCION daemon + bootstrap
+TS_SCION_EMBEDDED=1 \
+TS_SCION_BOOTSTRAP_URL=http://your-bootstrap-server:8041 \
+  tailscaled
 
-```
-go install tailscale.com/cmd/tailscale{,d}
+# Verify SCION is connected
+curl -s --unix-socket /var/run/tailscale/tailscaled.sock \
+  http://local-tailscaled.sock/localapi/v0/scion-status
+# {"Connected":true,"LocalIA":"19-ffaa:1:eba"}
 ```
 
-If you're packaging Tailscale for distribution, use `build_dist.sh`
-instead, to burn commit IDs and version info into the binaries:
+If you have a local SCION daemon (sciond) running, no environment variables are needed -- Tailscale will connect to it automatically at `127.0.0.1:30255`.
 
-```
-./build_dist.sh tailscale.com/cmd/tailscale
-./build_dist.sh tailscale.com/cmd/tailscaled
-```
+## Android
+
+See [netsys-lab/tailscale-android-scion](https://github.com/netsys-lab/tailscale-android-scion) for the Android client with SCION settings UI and live path display.
+
+## Connection Flow
+
+SCION connects using a cascading fallback:
 
-If your distro has conventions that preclude the use of
-`build_dist.sh`, please do the equivalent of what it does in your
-distro's way, so that bug reports contain useful version information.
+1. **External daemon** -- connects to sciond at `SCION_DAEMON_ADDRESS`. *Skipped if `TS_SCION_EMBEDDED=1`.*
+2. **Embedded daemon** -- loads local topology file (`TS_SCION_TOPOLOGY` or `/etc/scion/topology.json`). *Skipped if `TS_SCION_FORCE_BOOTSTRAP=1`.*
+3. **Bootstrap** -- fetches topology from: explicit URL → DNS SRV discovery → hardcoded defaults. Then starts embedded daemon with the fetched topology.
 
-## Bugs
+See [docs/architecture.md](docs/architecture.md) for details.
 
-Please file any issues about this code or the hosted service on
-[the issue tracker](https://github.com/tailscale/tailscale/issues).
+## Configuration
 
-## Contributing
+### Core
 
-PRs welcome! But please file bugs. Commit messages should [reference
-bugs](https://docs.github.com/en/github/writing-on-github/autolinked-references-and-urls).
+| Variable | Default | Description |
+|----------|---------|-------------|
+| `SCION_DAEMON_ADDRESS` | `127.0.0.1:30255` | External SCION daemon gRPC address |
+| `TS_SCION_EMBEDDED` | `false` | Skip external daemon, use embedded connector only |
+| `TS_PREFER_SCION` | `false` | Unconditionally prefer SCION over all other paths |
+| `TS_SCION_PREFERENCE` | `15` | betterAddr points bonus for SCION (0 to disable) |
+| `TS_SCION_PORT` | (auto) | Local SCION/UDP listen port |
+| `TS_SCION_LISTEN_ADDR` | (auto) | Listen address override |
+
+### Bootstrap & Topology
+
+| Variable | Default | Description |
+|----------|---------|-------------|
+| `TS_SCION_TOPOLOGY` | (auto) | Path to `topology.json` (defaults to `/etc/scion/topology.json` on Linux) |
+| `TS_SCION_BOOTSTRAP_URL` | (unset) | Single bootstrap server URL |
+| `TS_SCION_BOOTSTRAP_URLS` | (unset) | Comma-separated bootstrap server URLs |
+| `TS_SCION_FORCE_BOOTSTRAP` | `false` | Skip local topology, go straight to bootstrap |
+| `TS_SCION_STATE_DIR` | (auto) | State directory for bootstrap data and PathDB |
+
+### Advanced
+
+| Variable | Default | Description |
+|----------|---------|-------------|
+| `TS_SCION_MAX_PROBE_PATHS` | `5` | Max SCION paths to probe per peer |
+| `TS_SCION_DIVERSITY_THRESHOLD` | `50` | Latency penalty threshold (ms) for path diversity |
+| `TS_SCION_NO_FAST_PATH` | `false` | Disable pre-serialized fast-path sends |
+| `TS_SCION_NO_DISPATCHER_SHIM` | `false` | Disable legacy dispatcher port 30041 shim |
+
+## Build Tags
+
+Build without SCION support using the `ts_omit_scion` tag:
+
+```bash
+go install -tags ts_omit_scion tailscale.com/cmd/tailscale{,d}
+```
 
-We require [Developer Certificate of
-Origin](https://en.wikipedia.org/wiki/Developer_Certificate_of_Origin)
-`Signed-off-by` lines in commits.
+This compiles out all SCION code, producing a smaller binary with no `scionproto/scion` dependency.
 
-See [commit-messages.md](docs/commit-messages.md) (or skim `git log`) for our commit message style.
 
-## About Us
+## Architecture
 
-[Tailscale](https://tailscale.com/) is primarily developed by the
-people at https://github.com/orgs/tailscale/people. For other contributors,
-see:
+See [docs/architecture.md](docs/architecture.md) for component overview, data flow, and design decisions.
 
-* https://github.com/tailscale/tailscale/graphs/contributors
-* https://github.com/tailscale/tailscale-android/graphs/contributors
+## License
 
-## Legal
+BSD-3-Clause. Based on [tailscale/tailscale](https://github.com/tailscale/tailscale).
+SCION networking provided by [scionproto/scion](https://github.com/scionproto/scion) (Apache-2.0).
 
-WireGuard is a registered trademark of Jason A. Donenfeld.
+This project is not affiliated with or endorsed by Tailscale Inc.
+WireGuard is a registered trademark of Jason A. Donenfeld.
\ No newline at end of file
diff --git a/cmd/containerboot/kube.go b/cmd/containerboot/kube.go
index 4943bddba7ad4..73f5819b406db 100644
--- a/cmd/containerboot/kube.go
+++ b/cmd/containerboot/kube.go
@@ -14,9 +14,12 @@ import (
 	"net/http"
 	"net/netip"
 	"os"
+	"path/filepath"
 	"strings"
 	"time"
 
+	"github.com/fsnotify/fsnotify"
+	"tailscale.com/client/local"
 	"tailscale.com/ipn"
 	"tailscale.com/kube/egressservices"
 	"tailscale.com/kube/ingressservices"
@@ -26,9 +29,11 @@ import (
 	"tailscale.com/tailcfg"
 	"tailscale.com/types/logger"
 	"tailscale.com/util/backoff"
-	"tailscale.com/util/set"
 )
 
+const fieldManager = "tailscale-container"
+const kubeletMountedConfigLn = "..data"
+
 // kubeClient is a wrapper around Tailscale's internal kube client that knows how to talk to the kube API server. We use
 // this rather than any of the upstream Kubernetes client libaries to avoid extra imports.
 type kubeClient struct {
@@ -46,7 +51,7 @@ func newKubeClient(root string, stateSecret string) (*kubeClient, error) {
 	var err error
 	kc, err := kubeclient.New("tailscale-container")
 	if err != nil {
-		return nil, fmt.Errorf("Error creating kube client: %w", err)
+		return nil, fmt.Errorf("error creating kube client: %w", err)
 	}
 	if (root != "/") || os.Getenv("TS_KUBERNETES_READ_API_SERVER_ADDRESS_FROM_ENV") == "true" {
 		// Derive the API server address from the environment variables
@@ -63,7 +68,7 @@ func (kc *kubeClient) storeDeviceID(ctx context.Context, deviceID tailcfg.Stable
 			kubetypes.KeyDeviceID: []byte(deviceID),
 		},
 	}
-	return kc.StrategicMergePatchSecret(ctx, kc.stateSecret, s, "tailscale-container")
+	return kc.StrategicMergePatchSecret(ctx, kc.stateSecret, s, fieldManager)
 }
 
 // storeDeviceEndpoints writes device's tailnet IPs and MagicDNS name to fields 'device_ips', 'device_fqdn' of client's
@@ -84,7 +89,7 @@ func (kc *kubeClient) storeDeviceEndpoints(ctx context.Context, fqdn string, add
 			kubetypes.KeyDeviceIPs:  deviceIPs,
 		},
 	}
-	return kc.StrategicMergePatchSecret(ctx, kc.stateSecret, s, "tailscale-container")
+	return kc.StrategicMergePatchSecret(ctx, kc.stateSecret, s, fieldManager)
 }
 
 // storeHTTPSEndpoint writes an HTTPS endpoint exposed by this device via 'tailscale serve' to the client's state
@@ -96,7 +101,7 @@ func (kc *kubeClient) storeHTTPSEndpoint(ctx context.Context, ep string) error {
 			kubetypes.KeyHTTPSEndpoint: []byte(ep),
 		},
 	}
-	return kc.StrategicMergePatchSecret(ctx, kc.stateSecret, s, "tailscale-container")
+	return kc.StrategicMergePatchSecret(ctx, kc.stateSecret, s, fieldManager)
 }
 
 // deleteAuthKey deletes the 'authkey' field of the given kube
@@ -122,7 +127,7 @@ func (kc *kubeClient) deleteAuthKey(ctx context.Context) error {
 
 // resetContainerbootState resets state from previous runs of containerboot to
 // ensure the operator doesn't use stale state when a Pod is first recreated.
-func (kc *kubeClient) resetContainerbootState(ctx context.Context, podUID string) error {
+func (kc *kubeClient) resetContainerbootState(ctx context.Context, podUID string, tailscaledConfigAuthkey string) error {
 	existingSecret, err := kc.GetSecret(ctx, kc.stateSecret)
 	switch {
 	case kubeclient.IsNotFoundErr(err):
@@ -131,32 +136,135 @@ func (kc *kubeClient) resetContainerbootState(ctx context.Context, podUID string
 	case err != nil:
 		return fmt.Errorf("failed to read state Secret %q to reset state: %w", kc.stateSecret, err)
 	}
+
 	s := &kubeapi.Secret{
 		Data: map[string][]byte{
 			kubetypes.KeyCapVer: fmt.Appendf(nil, "%d", tailcfg.CurrentCapabilityVersion),
+
+			// TODO(tomhjp): Perhaps shouldn't clear device ID and use a different signal, as this could leak tailnet devices.
+			kubetypes.KeyDeviceID:            nil,
+			kubetypes.KeyDeviceFQDN:          nil,
+			kubetypes.KeyDeviceIPs:           nil,
+			kubetypes.KeyHTTPSEndpoint:       nil,
+			egressservices.KeyEgressServices: nil,
+			ingressservices.IngressConfigKey: nil,
 		},
 	}
 	if podUID != "" {
 		s.Data[kubetypes.KeyPodUID] = []byte(podUID)
 	}
 
-	toClear := set.SetOf([]string{
-		kubetypes.KeyDeviceID,
-		kubetypes.KeyDeviceFQDN,
-		kubetypes.KeyDeviceIPs,
-		kubetypes.KeyHTTPSEndpoint,
-		egressservices.KeyEgressServices,
-		ingressservices.IngressConfigKey,
-	})
-	for key := range existingSecret.Data {
-		if toClear.Contains(key) {
-			// It's fine to leave the key in place as a debugging breadcrumb,
-			// it should get a new value soon.
-			s.Data[key] = nil
+	// Only clear reissue_authkey if the operator has actioned it.
+	brokenAuthkey, ok := existingSecret.Data[kubetypes.KeyReissueAuthkey]
+	if ok && tailscaledConfigAuthkey != "" && string(brokenAuthkey) != tailscaledConfigAuthkey {
+		s.Data[kubetypes.KeyReissueAuthkey] = nil
+	}
+
+	return kc.StrategicMergePatchSecret(ctx, kc.stateSecret, s, fieldManager)
+}
+
+func (kc *kubeClient) setAndWaitForAuthKeyReissue(ctx context.Context, client *local.Client, cfg *settings, tailscaledConfigAuthKey string) error {
+	err := client.DisconnectControl(ctx)
+	if err != nil {
+		return fmt.Errorf("error disconnecting from control: %w", err)
+	}
+
+	err = kc.setReissueAuthKey(ctx, tailscaledConfigAuthKey)
+	if err != nil {
+		return fmt.Errorf("failed to set reissue_authkey in Kubernetes Secret: %w", err)
+	}
+
+	err = kc.waitForAuthKeyReissue(ctx, cfg.TailscaledConfigFilePath, tailscaledConfigAuthKey, 10*time.Minute)
+	if err != nil {
+		return fmt.Errorf("failed to receive new auth key: %w", err)
+	}
+
+	return nil
+}
+
+func (kc *kubeClient) setReissueAuthKey(ctx context.Context, authKey string) error {
+	s := &kubeapi.Secret{
+		Data: map[string][]byte{
+			kubetypes.KeyReissueAuthkey: []byte(authKey),
+		},
+	}
+
+	log.Printf("Requesting a new auth key from operator")
+	return kc.StrategicMergePatchSecret(ctx, kc.stateSecret, s, fieldManager)
+}
+
+func (kc *kubeClient) waitForAuthKeyReissue(ctx context.Context, configPath string, oldAuthKey string, maxWait time.Duration) error {
+	log.Printf("Waiting for operator to provide new auth key (max wait: %v)", maxWait)
+
+	ctx, cancel := context.WithTimeout(ctx, maxWait)
+	defer cancel()
+
+	tailscaledCfgDir := filepath.Dir(configPath)
+	toWatch := filepath.Join(tailscaledCfgDir, kubeletMountedConfigLn)
+
+	var (
+		pollTicker <-chan time.Time
+		eventChan  <-chan fsnotify.Event
+	)
+
+	pollInterval := 5 * time.Second
+
+	// Try to use fsnotify for faster notification
+	if w, err := fsnotify.NewWatcher(); err != nil {
+		log.Printf("auth key reissue: fsnotify unavailable, using polling: %v", err)
+	} else if err := w.Add(tailscaledCfgDir); err != nil {
+		w.Close()
+		log.Printf("auth key reissue: fsnotify watch failed, using polling: %v", err)
+	} else {
+		defer w.Close()
+		log.Printf("auth key reissue: watching for config changes via fsnotify")
+		eventChan = w.Events
+	}
+
+	// still keep polling if using fsnotify, for logging and in case fsnotify fails
+	pt := time.NewTicker(pollInterval)
+	defer pt.Stop()
+	pollTicker = pt.C
+
+	start := time.Now()
+
+	for {
+		select {
+		case <-ctx.Done():
+			return fmt.Errorf("timeout waiting for auth key reissue after %v", maxWait)
+		case <-pollTicker: // Waits for polling tick, continues when received
+		case event := <-eventChan:
+			if event.Name != toWatch {
+				continue
+			}
+		}
+
+		newAuthKey := authkeyFromTailscaledConfig(configPath)
+		if newAuthKey != "" && newAuthKey != oldAuthKey {
+			log.Printf("New auth key received from operator after %v", time.Since(start).Round(time.Second))
+
+			if err := kc.clearReissueAuthKeyRequest(ctx); err != nil {
+				log.Printf("Warning: failed to clear reissue request: %v", err)
+			}
+
+			return nil
+		}
+
+		if eventChan == nil && pollTicker != nil {
+			log.Printf("Waiting for new auth key from operator (%v elapsed)", time.Since(start).Round(time.Second))
 		}
 	}
+}
 
-	return kc.StrategicMergePatchSecret(ctx, kc.stateSecret, s, "tailscale-container")
+// clearReissueAuthKeyRequest removes the reissue_authkey marker from the Secret
+// to signal to the operator that we've successfully received the new key.
+func (kc *kubeClient) clearReissueAuthKeyRequest(ctx context.Context) error {
+	s := &kubeapi.Secret{
+		Data: map[string][]byte{
+			kubetypes.KeyReissueAuthkey: nil,
+		},
+	}
+	return kc.StrategicMergePatchSecret(ctx, kc.stateSecret, s, fieldManager)
 }
 
 // waitForConsistentState waits for tailscaled to finish writing state if it
diff --git a/cmd/containerboot/kube_test.go b/cmd/containerboot/kube_test.go
index bc80e9cdf2cb3..6acaa60e1588e 100644
--- a/cmd/containerboot/kube_test.go
+++ b/cmd/containerboot/kube_test.go
@@ -248,25 +248,42 @@ func TestResetContainerbootState(t *testing.T) {
 	capver := fmt.Appendf(nil, "%d", tailcfg.CurrentCapabilityVersion)
 	for name, tc := range map[string]struct {
 		podUID   string
+		authkey  string
 		initial  map[string][]byte
 		expected map[string][]byte
 	}{
 		"empty_initial": {
 			podUID:  "1234",
+			authkey: "new-authkey",
 			initial: map[string][]byte{},
 			expected: map[string][]byte{
 				kubetypes.KeyCapVer: capver,
 				kubetypes.KeyPodUID: []byte("1234"),
+				// Cleared keys.
+				kubetypes.KeyDeviceID:            nil,
+				kubetypes.KeyDeviceFQDN:          nil,
+				kubetypes.KeyDeviceIPs:           nil,
+				kubetypes.KeyHTTPSEndpoint:       nil,
+				egressservices.KeyEgressServices: nil,
+				ingressservices.IngressConfigKey: nil,
 			},
 		},
 		"empty_initial_no_pod_uid": {
 			initial: map[string][]byte{},
 			expected: map[string][]byte{
 				kubetypes.KeyCapVer: capver,
+				// Cleared keys.
+				kubetypes.KeyDeviceID:            nil,
+				kubetypes.KeyDeviceFQDN:          nil,
+				kubetypes.KeyDeviceIPs:           nil,
+				kubetypes.KeyHTTPSEndpoint:       nil,
+				egressservices.KeyEgressServices: nil,
+				ingressservices.IngressConfigKey: nil,
 			},
 		},
 		"only_relevant_keys_updated": {
-			podUID: "1234",
+			podUID:  "1234",
+			authkey: "new-authkey",
 			initial: map[string][]byte{
 				kubetypes.KeyCapVer:              []byte("1"),
 				kubetypes.KeyPodUID:              []byte("5678"),
@@ -295,6 +312,57 @@ func TestResetContainerbootState(t *testing.T) {
 				// Tailscaled keys not included in patch.
 			},
 		},
+		"new_authkey_issued": {
+			initial: map[string][]byte{
+				kubetypes.KeyReissueAuthkey: []byte("old-authkey"),
+			},
+			authkey: "new-authkey",
+			expected: map[string][]byte{
+				kubetypes.KeyCapVer:         capver,
+				kubetypes.KeyReissueAuthkey: nil,
+				// Cleared keys.
+				kubetypes.KeyDeviceID:            nil,
+				kubetypes.KeyDeviceFQDN:          nil,
+				kubetypes.KeyDeviceIPs:           nil,
+				kubetypes.KeyHTTPSEndpoint:       nil,
+				egressservices.KeyEgressServices: nil,
+				ingressservices.IngressConfigKey: nil,
+			},
+		},
+		"authkey_not_yet_updated": {
+			initial: map[string][]byte{
+				kubetypes.KeyReissueAuthkey: []byte("old-authkey"),
+			},
+			authkey: "old-authkey",
+			expected: map[string][]byte{
+				kubetypes.KeyCapVer: capver,
+				// reissue_authkey not cleared.
+				// Cleared keys.
+				kubetypes.KeyDeviceID:            nil,
+				kubetypes.KeyDeviceFQDN:          nil,
+				kubetypes.KeyDeviceIPs:           nil,
+				kubetypes.KeyHTTPSEndpoint:       nil,
+				egressservices.KeyEgressServices: nil,
+				ingressservices.IngressConfigKey: nil,
+			},
+		},
+		"authkey_deleted_from_config": {
+			initial: map[string][]byte{
+				kubetypes.KeyReissueAuthkey: []byte("old-authkey"),
+			},
+			authkey: "",
+			expected: map[string][]byte{
+				kubetypes.KeyCapVer: capver,
+				// reissue_authkey not cleared.
+				// Cleared keys.
+				kubetypes.KeyDeviceID:            nil,
+				kubetypes.KeyDeviceFQDN:          nil,
+				kubetypes.KeyDeviceIPs:           nil,
+				kubetypes.KeyHTTPSEndpoint:       nil,
+				egressservices.KeyEgressServices: nil,
+				ingressservices.IngressConfigKey: nil,
+			},
+		},
 	} {
 		t.Run(name, func(t *testing.T) {
 			var actual map[string][]byte
@@ -309,7 +377,7 @@ func TestResetContainerbootState(t *testing.T) {
 					return nil
 				},
 			}}
-			if err := kc.resetContainerbootState(context.Background(), tc.podUID); err != nil {
+			if err := kc.resetContainerbootState(context.Background(), tc.podUID, tc.authkey); err != nil {
 				t.Fatalf("resetContainerbootState() error = %v", err)
 			}
 			if diff := cmp.Diff(tc.expected, actual); diff != "" {
diff --git a/cmd/containerboot/main.go b/cmd/containerboot/main.go
index ba47111fd797f..76c6e910a9dbc 100644
--- a/cmd/containerboot/main.go
+++ b/cmd/containerboot/main.go
@@ -137,7 +137,9 @@ import (
 
 	"golang.org/x/sys/unix"
 	"tailscale.com/client/tailscale"
+	"tailscale.com/health"
 	"tailscale.com/ipn"
+	"tailscale.com/ipn/conffile"
 	kubeutils "tailscale.com/k8s-operator"
 	healthz "tailscale.com/kube/health"
 	"tailscale.com/kube/kubetypes"
@@ -206,6 +208,11 @@ func run() error {
 	bootCtx, cancel := context.WithTimeout(ctx, 60*time.Second)
 	defer cancel()
 
+	var tailscaledConfigAuthkey string
+	if isOneStepConfig(cfg) {
+		tailscaledConfigAuthkey = authkeyFromTailscaledConfig(cfg.TailscaledConfigFilePath)
+	}
+
 	var kc *kubeClient
 	if cfg.KubeSecret != "" {
 		kc, err = newKubeClient(cfg.Root, cfg.KubeSecret)
@@ -219,7 +226,7 @@ func run() error {
 		// hasKubeStateStore because although we know we're in kube, that
 		// doesn't guarantee the state store is properly configured.
 		if hasKubeStateStore(cfg) {
-			if err := kc.resetContainerbootState(bootCtx, cfg.PodUID); err != nil {
+			if err := kc.resetContainerbootState(bootCtx, cfg.PodUID, tailscaledConfigAuthkey); err != nil {
 				return fmt.Errorf("error clearing previous state from Secret: %w", err)
 			}
 		}
@@ -299,7 +306,7 @@ func run() error {
 		}
 	}
 
-	w, err := client.WatchIPNBus(bootCtx, ipn.NotifyInitialNetMap|ipn.NotifyInitialPrefs|ipn.NotifyInitialState)
+	w, err := client.WatchIPNBus(bootCtx, ipn.NotifyInitialNetMap|ipn.NotifyInitialPrefs|ipn.NotifyInitialState|ipn.NotifyInitialHealthState)
 	if err != nil {
 		return fmt.Errorf("failed to watch tailscaled for updates: %w", err)
 	}
@@ -365,8 +372,23 @@ authLoop:
 				if isOneStepConfig(cfg) {
 					// This could happen if this is the first time tailscaled was run for this
 					// device and the auth key was not passed via the configfile.
-					return fmt.Errorf("invalid state: tailscaled daemon started with a config file, but tailscale is not logged in: ensure you pass a valid auth key in the config file.")
+					if hasKubeStateStore(cfg) {
+						log.Printf("Auth key missing or invalid (NeedsLogin state), disconnecting from control and requesting new key from operator")
+
+						err := kc.setAndWaitForAuthKeyReissue(bootCtx, client, cfg, tailscaledConfigAuthkey)
+						if err != nil {
+							return fmt.Errorf("failed to get a reissued authkey: %w", err)
+						}
+
+						log.Printf("Successfully received new auth key, restarting to apply configuration")
+
+						// we don't return an error here since we have handled the reissue gracefully.
+						return nil
+					}
+
+					return errors.New("invalid state: tailscaled daemon started with a config file, but tailscale is not logged in: ensure you pass a valid auth key in the config file")
 				}
+
 				if err := authTailscale(); err != nil {
 					return fmt.Errorf("failed to auth tailscale: %w", err)
 				}
@@ -384,6 +406,27 @@ authLoop:
 				log.Printf("tailscaled in state %q, waiting", *n.State)
 			}
 		}
+
+		if n.Health != nil {
+			// This can happen if the config has an auth key but it's invalid,
+			// for example if it was single-use and already got used, but the
+			// device state was lost.
+			if _, ok := n.Health.Warnings[health.LoginStateWarnable.Code]; ok {
+				if isOneStepConfig(cfg) && hasKubeStateStore(cfg) {
+					log.Printf("Auth key failed to authenticate (may be expired or single-use), disconnecting from control and requesting new key from operator")
+
+					err := kc.setAndWaitForAuthKeyReissue(bootCtx, client, cfg, tailscaledConfigAuthkey)
+					if err != nil {
+						return fmt.Errorf("failed to get a reissued authkey: %w", err)
+					}
+
+					// we don't return an error here since we have handled the reissue gracefully.
+					log.Printf("Successfully received new auth key, restarting to apply configuration")
+
+					return nil
+				}
+			}
+		}
 	}
 
 	w.Close()
@@ -409,9 +452,9 @@ authLoop:
 		// We were told to only auth once, so any secret-bound
 		// authkey is no longer needed. We don't strictly need to
 		// wipe it, but it's good hygiene.
-		log.Printf("Deleting authkey from kube secret")
+		log.Printf("Deleting authkey from Kubernetes Secret")
 		if err := kc.deleteAuthKey(ctx); err != nil {
-			return fmt.Errorf("deleting authkey from kube secret: %w", err)
+			return fmt.Errorf("deleting authkey from Kubernetes Secret: %w", err)
 		}
 	}
 
@@ -422,8 +465,10 @@ authLoop:
 
 	// If tailscaled config was read from a mounted file, watch the file for updates and reload.
 	cfgWatchErrChan := make(chan error)
+	cfgWatchCtx, cfgWatchCancel := context.WithCancel(ctx)
+	defer cfgWatchCancel()
 	if cfg.TailscaledConfigFilePath != "" {
-		go watchTailscaledConfigChanges(ctx, cfg.TailscaledConfigFilePath, client, cfgWatchErrChan)
+		go watchTailscaledConfigChanges(cfgWatchCtx, cfg.TailscaledConfigFilePath, client, cfgWatchErrChan)
 	}
 
 	var (
@@ -523,6 +568,7 @@ runLoop:
 		case err := <-cfgWatchErrChan:
 			return fmt.Errorf("failed to watch tailscaled config: %w", err)
 		case n := <-notifyChan:
+			// TODO: (ChaosInTheCRD) Add node removed check when supported by ipn
 			if n.State != nil && *n.State != ipn.Running {
 				// Something's gone wrong and we've left the authenticated state.
 				// Our container image never recovered gracefully from this, and the
@@ -979,3 +1025,11 @@ func serviceIPsFromNetMap(nm *netmap.NetworkMap, fqdn dnsname.FQDN) []netip.Pref
 
 	return prefixes
 }
+
+func authkeyFromTailscaledConfig(path string) string {
+	if cfg, err := conffile.Load(path); err == nil && cfg.Parsed.AuthKey != nil {
+		return *cfg.Parsed.AuthKey
+	}
+
+	return ""
+}
diff --git a/cmd/containerboot/main_test.go b/cmd/containerboot/main_test.go
index 365cf218424de..5ea402f6678c9 100644
--- a/cmd/containerboot/main_test.go
+++ b/cmd/containerboot/main_test.go
@@ -32,6 +32,7 @@ import (
 
 	"github.com/google/go-cmp/cmp"
 	"golang.org/x/sys/unix"
+	"tailscale.com/health"
 	"tailscale.com/ipn"
 	"tailscale.com/kube/egressservices"
 	"tailscale.com/kube/kubeclient"
@@ -41,6 +42,8 @@ import (
 	"tailscale.com/types/netmap"
 )
 
+const configFileAuthKey = "some-auth-key"
+
 func TestContainerBoot(t *testing.T) {
 	boot := filepath.Join(t.TempDir(), "containerboot")
 	if err := exec.Command("go", "build", "-ldflags", "-X main.testSleepDuration=1ms", "-o", boot, "tailscale.com/cmd/containerboot").Run(); err != nil {
@@ -77,6 +80,10 @@ func TestContainerBoot(t *testing.T) {
 		// phase (simulates our fake tailscaled doing it).
 		UpdateKubeSecret map[string]string
 
+		// Update files with these paths/contents at the beginning of the phase
+		// (simulates the operator updating mounted config files).
+		UpdateFiles map[string]string
+
 		// WantFiles files that should exist in the container and their
 		// contents.
 		WantFiles map[string]string
@@ -781,6 +788,127 @@ func TestContainerBoot(t *testing.T) {
 				},
 			}
 		},
+		"sets_reissue_authkey_if_needs_login": func(env *testEnv) testCase {
+			newAuthKey := "new-reissued-auth-key"
+			return testCase{
+				Env: map[string]string{
+					"TS_EXPERIMENTAL_VERSIONED_CONFIG_DIR": filepath.Join(env.d, "etc/tailscaled/"),
+					"KUBERNETES_SERVICE_HOST":              env.kube.Host,
+					"KUBERNETES_SERVICE_PORT_HTTPS":        env.kube.Port,
+				},
+				Phases: []phase{
+					{
+						UpdateFiles: map[string]string{
+							"etc/tailscaled/..data": "",
+						},
+						WantCmds: []string{
+							"/usr/bin/tailscaled --socket=/tmp/tailscaled.sock --state=kube:tailscale --statedir=/tmp --tun=userspace-networking --config=/etc/tailscaled/cap-95.hujson",
+						},
+						WantKubeSecret: map[string]string{
+							kubetypes.KeyCapVer: capver,
+						},
+					}, {
+						Notify: &ipn.Notify{
+							State: new(ipn.NeedsLogin),
+						},
+						WantKubeSecret: map[string]string{
+							kubetypes.KeyCapVer:         capver,
+							kubetypes.KeyReissueAuthkey: configFileAuthKey,
+						},
+						WantLog: "watching for config changes via fsnotify",
+					}, {
+						UpdateFiles: map[string]string{
+							"etc/tailscaled/cap-95.hujson": fmt.Sprintf(`{"Version":"alpha0","AuthKey":"%s"}`, newAuthKey),
+							"etc/tailscaled/..data":        "updated",
+						},
+						WantKubeSecret: map[string]string{
+							kubetypes.KeyCapVer: capver,
+						},
+						WantExitCode: new(0),
+						WantLog:      "Successfully received new auth key, restarting to apply configuration",
+					},
+				},
+			}
+		},
+		"sets_reissue_authkey_if_auth_fails": func(env *testEnv) testCase {
+			newAuthKey := "new-reissued-auth-key"
+			return testCase{
+				Env: map[string]string{
+					"TS_EXPERIMENTAL_VERSIONED_CONFIG_DIR": filepath.Join(env.d, "etc/tailscaled/"),
+					"KUBERNETES_SERVICE_HOST":              env.kube.Host,
+					"KUBERNETES_SERVICE_PORT_HTTPS":        env.kube.Port,
+				},
+				Phases: []phase{
+					{
+						UpdateFiles: map[string]string{
+							"etc/tailscaled/..data": "",
+						},
+						WantCmds: []string{
+							"/usr/bin/tailscaled --socket=/tmp/tailscaled.sock --state=kube:tailscale --statedir=/tmp --tun=userspace-networking --config=/etc/tailscaled/cap-95.hujson",
+						},
+						WantKubeSecret: map[string]string{
+							kubetypes.KeyCapVer: capver,
+						},
+					}, {
+						Notify: &ipn.Notify{
+							Health: &health.State{
+								Warnings: map[health.WarnableCode]health.UnhealthyState{
+									health.LoginStateWarnable.Code: {},
+								},
+							},
+						},
+						WantKubeSecret: map[string]string{
+							kubetypes.KeyCapVer:         capver,
+							kubetypes.KeyReissueAuthkey: configFileAuthKey,
+						},
+						WantLog: "watching for config changes via fsnotify",
+					}, {
+						UpdateFiles: map[string]string{
+							"etc/tailscaled/cap-95.hujson": fmt.Sprintf(`{"Version":"alpha0","AuthKey":"%s"}`, newAuthKey),
+							"etc/tailscaled/..data":        "updated",
+						},
+						WantKubeSecret: map[string]string{
+							kubetypes.KeyCapVer: capver,
+						},
+						WantExitCode: new(0),
+						WantLog:      "Successfully received new auth key, restarting to apply configuration",
+					},
+				},
+			}
+		},
+		"clears_reissue_authkey_on_change": func(env *testEnv) testCase {
+			return testCase{
+				Env: map[string]string{
+					"TS_EXPERIMENTAL_VERSIONED_CONFIG_DIR": filepath.Join(env.d, "etc/tailscaled/"),
+					"KUBERNETES_SERVICE_HOST":              env.kube.Host,
+					"KUBERNETES_SERVICE_PORT_HTTPS":        env.kube.Port,
+				},
+				KubeSecret: map[string]string{
+					kubetypes.KeyReissueAuthkey: "some-older-authkey",
+					"foo":                       "bar", // Check not everything is cleared.
+				},
+				Phases: []phase{
+					{
+						WantCmds: []string{
+							"/usr/bin/tailscaled --socket=/tmp/tailscaled.sock --state=kube:tailscale --statedir=/tmp --tun=userspace-networking --config=/etc/tailscaled/cap-95.hujson",
+						},
+						WantKubeSecret: map[string]string{
+							kubetypes.KeyCapVer: capver,
+							"foo":               "bar",
+						},
+					}, {
+						Notify: runningNotify,
+						WantKubeSecret: map[string]string{
+							kubetypes.KeyCapVer:     capver,
+							"foo":                   "bar",
+							kubetypes.KeyDeviceFQDN: "test-node.test.ts.net.",
+							kubetypes.KeyDeviceID:   "myID",
+							kubetypes.KeyDeviceIPs:  `["100.64.0.1"]`,
+						},
+					},
+				},
+			}
+		},
 		"metrics_enabled": func(env *testEnv) testCase {
 			return testCase{
 				Env: map[string]string{
@@ -1134,19 +1262,22 @@ func TestContainerBoot(t *testing.T) {
 				for k, v := range p.UpdateKubeSecret {
 					env.kube.SetSecret(k, v)
 				}
+				for path, content := range p.UpdateFiles {
+					fullPath := filepath.Join(env.d, path)
+					if err := os.WriteFile(fullPath, []byte(content), 0700); err != nil {
+						t.Fatalf("phase %d: updating file %q: %v", i, path, err)
+					}
+					// Explicitly update mtime to ensure fsnotify detects the change.
+					// Without this, file operations can be buffered and fsnotify events may not trigger.
+					now := time.Now()
+					if err := os.Chtimes(fullPath, now, now); err != nil {
+						t.Fatalf("phase %d: updating mtime for %q: %v", i, path, err)
+					}
+				}
 				env.lapi.Notify(p.Notify)
 				if p.Signal != nil {
 					cmd.Process.Signal(*p.Signal)
 				}
-				if p.WantLog != "" {
-					err := tstest.WaitFor(2*time.Second, func() error {
-						waitLogLine(t, time.Second, cbOut, p.WantLog)
-						return nil
-					})
-					if err != nil {
-						t.Fatal(err)
-					}
-				}
 
 				if p.WantExitCode != nil {
 					state, err := cmd.Process.Wait()
@@ -1156,14 +1287,19 @@ func TestContainerBoot(t *testing.T) {
 					if state.ExitCode() != *p.WantExitCode {
 						t.Fatalf("phase %d: want exit code %d, got %d", i, *p.WantExitCode, state.ExitCode())
 					}
+				}
 
-					// Early test return, we don't expect the successful startup log message.
-					return
+				if p.WantLog != "" {
+					err := tstest.WaitFor(5*time.Second, func() error {
+						waitLogLine(t, 5*time.Second, cbOut, p.WantLog)
+						return nil
+					})
+					if err != nil {
+						t.Fatal(err)
+					}
 				}
 
-				wantCmds = append(wantCmds, p.WantCmds...)
-				waitArgs(t, 2*time.Second, env.d, env.argFile, strings.Join(wantCmds, "\n"))
-				err := tstest.WaitFor(2*time.Second, func() error {
+				err := tstest.WaitFor(5*time.Second, func() error {
 					if p.WantKubeSecret != nil {
 						got := env.kube.Secret()
 						if diff := cmp.Diff(got, p.WantKubeSecret); diff != "" {
@@ -1180,6 +1316,16 @@ func TestContainerBoot(t *testing.T) {
 				if err != nil {
 					t.Fatalf("test: %q phase %d: %v", name, i, err)
 				}
+
+				// if we provide a wanted exit code, we expect that the process is finished,
+				// so should return from the test.
+				if p.WantExitCode != nil {
+					return
+				}
+
+				wantCmds = append(wantCmds, p.WantCmds...)
+				waitArgs(t, 2*time.Second, env.d, env.argFile, strings.Join(wantCmds, "\n"))
+
 				err = tstest.WaitFor(2*time.Second, func() error {
 					for path, want := range p.WantFiles {
 						gotBs, err := os.ReadFile(filepath.Join(env.d, path))
@@ -1393,6 +1539,13 @@ func (lc *localAPI) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		default:
 			panic(fmt.Sprintf("unsupported method %q", r.Method))
 		}
+	// In the localAPI ServeHTTP method
+	case "/localapi/v0/disconnect-control":
+		if r.Method != "POST" {
+			panic(fmt.Sprintf("unsupported method %q", r.Method))
+		}
+		w.WriteHeader(http.StatusOK)
+		return
 	default:
 		panic(fmt.Sprintf("unsupported path %q", r.URL.Path))
 	}
@@ -1591,7 +1744,11 @@ func (k *kubeServer) serveSecret(w http.ResponseWriter, r *http.Request) {
 				panic(fmt.Sprintf("json decode failed: %v. Body:\n\n%s", err, string(bs)))
 			}
 			for key, val := range req.Data {
-				k.secret[key] = string(val)
+				if val == nil {
+					delete(k.secret, key)
+				} else {
+					k.secret[key] = string(val)
+				}
 			}
 		default:
 			panic(fmt.Sprintf("unknown content type %q", r.Header.Get("Content-Type")))
@@ -1659,7 +1816,7 @@ func newTestEnv(t *testing.T) testEnv {
 	kube.Start(t)
 	t.Cleanup(kube.Close)
 
-	tailscaledConf := &ipn.ConfigVAlpha{AuthKey: new("foo"), Version: "alpha0"}
+	tailscaledConf := &ipn.ConfigVAlpha{AuthKey: new(configFileAuthKey), Version: "alpha0"}
 	serveConf := ipn.ServeConfig{TCP: map[uint16]*ipn.TCPPortHandler{80: {HTTP: true}}}
 	serveConfWithServices := ipn.ServeConfig{
 		TCP: map[uint16]*ipn.TCPPortHandler{80: {HTTP: true}},
diff --git a/cmd/k8s-operator/e2e/ingress_test.go b/cmd/k8s-operator/e2e/ingress_test.go
index 95fbbab9df697..a136d2ad358e2 100644
--- a/cmd/k8s-operator/e2e/ingress_test.go
+++ b/cmd/k8s-operator/e2e/ingress_test.go
@@ -5,7 +5,6 @@ package e2e
 
 import (
 	"context"
-	"encoding/json"
 	"fmt"
 	"net/http"
 	"testing"
@@ -14,10 +13,6 @@ import (
 	appsv1 "k8s.io/api/apps/v1"
 	corev1 "k8s.io/api/core/v1"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
-	"k8s.io/apimachinery/pkg/util/wait"
-	"k8s.io/client-go/kubernetes"
-	"sigs.k8s.io/controller-runtime/pkg/client"
-	"sigs.k8s.io/yaml"
 
 	"tailscale.com/cmd/testwrapper/flakytest"
 	kube "tailscale.com/k8s-operator"
@@ -90,81 +85,20 @@ func TestIngress(t *testing.T) {
 	}
 	createAndCleanup(t, kubeClient, svc)
 
-	// TODO(tomhjp): Delete once we've reproduced the flake with this extra info.
-	t0 := time.Now()
-	watcherCtx, cancelWatcher := context.WithCancel(t.Context())
-	defer cancelWatcher()
-	go func() {
-		// client-go client for logs.
-		clientGoKubeClient, err := kubernetes.NewForConfig(restCfg)
-		if err != nil {
-			t.Logf("error creating client-go Kubernetes client: %v", err)
-			return
-		}
-
-		for {
-			select {
-			case <-watcherCtx.Done():
-				t.Logf("stopping watcher after %v", time.Since(t0))
-				return
-			case <-time.After(time.Minute):
-				t.Logf("dumping info after %v elapsed", time.Since(t0))
-				// Service itself.
-				svc := &corev1.Service{ObjectMeta: objectMeta("default", "test-ingress")}
-				err := get(watcherCtx, kubeClient, svc)
-				svcYaml, _ := yaml.Marshal(svc)
-				t.Logf("Service: %s, error: %v\n%s", svc.Name, err, string(svcYaml))
-
-				// Pods in tailscale namespace.
-				var pods corev1.PodList
-				if err := kubeClient.List(watcherCtx, &pods, client.InNamespace("tailscale")); err != nil {
-					t.Logf("error listing Pods in tailscale namespace: %v", err)
-				} else {
-					t.Logf("%d Pods", len(pods.Items))
-					for _, pod := range pods.Items {
-						podYaml, _ := yaml.Marshal(pod)
-						t.Logf("Pod: %s\n%s", pod.Name, string(podYaml))
-						logs := clientGoKubeClient.CoreV1().Pods("tailscale").GetLogs(pod.Name, &corev1.PodLogOptions{}).Do(watcherCtx)
-						logData, err := logs.Raw()
-						if err != nil {
-							t.Logf("error reading logs for Pod %s: %v", pod.Name, err)
-							continue
-						}
-						t.Logf("Logs for Pod %s:\n%s", pod.Name, string(logData))
-					}
-				}
-
-				// Tailscale status on the tailnet.
-				lc, err := tnClient.LocalClient()
-				if err != nil {
-					t.Logf("error getting tailnet local client: %v", err)
-				} else {
-					status, err := lc.Status(watcherCtx)
-					statusJSON, _ := json.MarshalIndent(status, "", "  ")
-					t.Logf("Tailnet status: %s, error: %v", string(statusJSON), err)
-				}
-			}
-		}
-	}()
-
-	// TODO: instead of timing out only when test times out, cancel context after 60s or so.
-	if err := wait.PollUntilContextCancel(t.Context(), time.Millisecond*100, true, func(ctx context.Context) (done bool, err error) {
-		if time.Since(t0) > time.Minute {
-			t.Logf("%v elapsed waiting for Service default/test-ingress to become Ready", time.Since(t0))
-		}
+	if err := tstest.WaitFor(time.Minute, func() error {
 		maybeReadySvc := &corev1.Service{ObjectMeta: objectMeta("default", "test-ingress")}
-		if err := get(ctx, kubeClient, maybeReadySvc); err != nil {
-			return false, err
+		if err := get(t.Context(), kubeClient, maybeReadySvc); err != nil {
+			return err
 		}
 		isReady := kube.SvcIsReady(maybeReadySvc)
 		if isReady {
 			t.Log("Service is ready")
+			return nil
 		}
-		return isReady, nil
+		return fmt.Errorf("Service is not ready yet")
 	}); err != nil {
 		t.Fatalf("error waiting for the Service to become Ready: %v", err)
 	}
-	cancelWatcher()
 
 	var resp *http.Response
 	if err := tstest.WaitFor(time.Minute, func() error {
diff --git a/cmd/k8s-operator/e2e/setup.go b/cmd/k8s-operator/e2e/setup.go
index c4fd45d3e4125..e3d7ed89b55ca 100644
--- a/cmd/k8s-operator/e2e/setup.go
+++ b/cmd/k8s-operator/e2e/setup.go
@@ -56,6 +56,7 @@ import (
 	"tailscale.com/internal/client/tailscale"
 	"tailscale.com/ipn"
 	"tailscale.com/ipn/store/mem"
+	tsoperator "tailscale.com/k8s-operator"
 	tsapi "tailscale.com/k8s-operator/apis/v1alpha1"
 	"tailscale.com/tsnet"
 )
@@ -438,7 +439,7 @@ func runTests(m *testing.M) (int, error) {
 		return 0, fmt.Errorf("failed to install %q via helm: %w", relName, err)
 	}
 
-	if err := applyDefaultProxyClass(ctx, kubeClient); err != nil {
+	if err := applyDefaultProxyClass(ctx, logger, kubeClient); err != nil {
 		return 0, fmt.Errorf("failed to apply default ProxyClass: %w", err)
 	}
 
@@ -537,7 +538,7 @@ func tagForRepo(dir string) (string, error) {
 	return tag, nil
 }
 
-func applyDefaultProxyClass(ctx context.Context, cl client.Client) error {
+func applyDefaultProxyClass(ctx context.Context, logger *zap.SugaredLogger, cl client.Client) error {
 	pc := &tsapi.ProxyClass{
 		TypeMeta: metav1.TypeMeta{
 			APIVersion: tsapi.SchemeGroupVersion.String(),
@@ -565,6 +566,24 @@ func applyDefaultProxyClass(ctx context.Context, cl client.Client) error {
 		return fmt.Errorf("failed to apply default ProxyClass: %w", err)
 	}
 
+	// Wait for the ProxyClass to be marked ready.
+	ctx, cancel := context.WithTimeout(ctx, time.Minute)
+	defer cancel()
+	for {
+		if err := cl.Get(ctx, client.ObjectKeyFromObject(pc), pc); err != nil {
+			return fmt.Errorf("failed to get default ProxyClass: %w", err)
+		}
+		if tsoperator.ProxyClassIsReady(pc) {
+			break
+		}
+		logger.Info("waiting for default ProxyClass to be ready...")
+		select {
+		case <-ctx.Done():
+			return fmt.Errorf("timeout waiting for default ProxyClass to be ready")
+		case <-time.After(time.Second):
+		}
+	}
+
 	return nil
 }
 
diff --git a/cmd/k8s-operator/operator.go b/cmd/k8s-operator/operator.go
index ef55d27481266..d353c53337fd6 100644
--- a/cmd/k8s-operator/operator.go
+++ b/cmd/k8s-operator/operator.go
@@ -20,6 +20,7 @@ import (
 	"github.com/go-logr/zapr"
 	"go.uber.org/zap"
 	"go.uber.org/zap/zapcore"
+	"golang.org/x/time/rate"
 	appsv1 "k8s.io/api/apps/v1"
 	corev1 "k8s.io/api/core/v1"
 	discoveryv1 "k8s.io/api/discovery/v1"
@@ -76,6 +77,12 @@ import (
 // Generate CRD API docs.
 //go:generate go run github.com/elastic/crd-ref-docs --renderer=markdown --source-path=../../k8s-operator/apis/ --config=../../k8s-operator/api-docs-config.yaml --output-path=../../k8s-operator/api.md
 
+const (
+	indexServiceProxyClass = ".metadata.annotations.service-proxy-class"
+	indexServiceExposed    = ".metadata.annotations.service-expose"
+	indexServiceType       = ".metadata.annotations.service-type"
+)
+
 func main() {
 	// Required to use our client API. We're fine with the instability since the
 	// client lives in the same repo as this code.
@@ -350,7 +357,12 @@ func runReconcilers(opts reconcilerOpts) {
 	svcChildFilter := handler.EnqueueRequestsFromMapFunc(managedResourceHandlerForType("svc"))
 	// If a ProxyClass changes, enqueue all Services labeled with that
 	// ProxyClass's name.
-	proxyClassFilterForSvc := handler.EnqueueRequestsFromMapFunc(proxyClassHandlerForSvc(mgr.GetClient(), startlog))
+	proxyClassFilterForSvc := handler.EnqueueRequestsFromMapFunc(proxyClassHandlerForSvc(
+		mgr.GetClient(),
+		startlog,
+		opts.defaultProxyClass,
+		opts.proxyActAsDefaultLoadBalancer,
+	))
 
 	eventRecorder := mgr.GetEventRecorderFor("tailscale-operator")
 	ssr := &tailscaleSTSReconciler{
@@ -388,6 +400,18 @@ func runReconcilers(opts reconcilerOpts) {
 	if err := mgr.GetFieldIndexer().IndexField(context.Background(), new(corev1.Service), indexServiceProxyClass, indexProxyClass); err != nil {
 		startlog.Fatalf("failed setting up ProxyClass indexer for Services: %v", err)
 	}
+	if opts.defaultProxyClass != "" {
+		// If a default ProxyClass is specified, we'll need to list all objects
+		// that could be affected. For L3 ingress, this is Services with the
+		// "tailscale.com/expose" annotation and LoadBalancer services (either
+		// with the loadBalancerClass "tailscale", or unset if we're the default).
+		if err := mgr.GetFieldIndexer().IndexField(context.Background(), new(corev1.Service), indexServiceExposed, indexExposed); err != nil {
+			startlog.Fatalf("failed setting up exposed indexer for Services: %v", err)
+		}
+		if err := mgr.GetFieldIndexer().IndexField(context.Background(), new(corev1.Service), indexServiceType, indexType); err != nil {
+			startlog.Fatalf("failed setting up type indexer for Services: %v", err)
+		}
+	}
 
 	ingressChildFilter := handler.EnqueueRequestsFromMapFunc(managedResourceHandlerForType("ingress"))
 	// If a ProxyClassChanges, enqueue all Ingresses labeled with that
@@ -723,6 +747,8 @@ func runReconcilers(opts reconcilerOpts) {
 			tsFirewallMode:    opts.proxyFirewallMode,
 			defaultProxyClass: opts.defaultProxyClass,
 			loginServer:       opts.tsServer.ControlURL,
+			authKeyRateLimits: make(map[string]*rate.Limiter),
+			authKeyReissuing:  make(map[string]bool),
 		})
 	if err != nil {
 		startlog.Fatalf("could not create ProxyGroup reconciler: %v", err)
@@ -907,10 +933,27 @@ func indexProxyClass(o client.Object) []string {
 	return []string{o.GetAnnotations()[LabelAnnotationProxyClass]}
 }
 
+func indexExposed(o client.Object) []string {
+	if o.GetAnnotations()[AnnotationExpose] != "true" {
+		return nil
+	}
+
+	return []string{o.GetAnnotations()[AnnotationExpose]}
+}
+
+func indexType(o client.Object) []string {
+	svc, ok := o.(*corev1.Service)
+	if !ok {
+		return nil
+	}
+
+	return []string{string(svc.Spec.Type)}
+}
+
 // proxyClassHandlerForSvc returns a handler that, for a given ProxyClass,
 // returns a list of reconcile requests for all Services labeled with
 // tailscale.com/proxy-class: <proxy class name>.
-func proxyClassHandlerForSvc(cl client.Client, logger *zap.SugaredLogger) handler.MapFunc {
+func proxyClassHandlerForSvc(cl client.Client, logger *zap.SugaredLogger, defaultProxyClass string, isDefaultLoadBalancer bool) handler.MapFunc {
 	return func(ctx context.Context, o client.Object) []reconcile.Request {
 		svcList := new(corev1.ServiceList)
 		labels := map[string]string{
@@ -929,13 +972,12 @@ func proxyClassHandlerForSvc(cl client.Client, logger *zap.SugaredLogger) handle
 			seenSvcs.Add(fmt.Sprintf("%s/%s", svc.Namespace, svc.Name))
 		}
 
-		svcAnnotationList := new(corev1.ServiceList)
-		if err := cl.List(ctx, svcAnnotationList, client.MatchingFields{indexServiceProxyClass: o.GetName()}); err != nil {
+		if err := cl.List(ctx, svcList, client.MatchingFields{indexServiceProxyClass: o.GetName()}); err != nil {
 			logger.Debugf("error listing Services for ProxyClass: %v", err)
 			return nil
 		}
 
-		for _, svc := range svcAnnotationList.Items {
+		for _, svc := range svcList.Items {
 			nsname := fmt.Sprintf("%s/%s", svc.Namespace, svc.Name)
 			if seenSvcs.Contains(nsname) {
 				continue
@@ -945,6 +987,36 @@ func proxyClassHandlerForSvc(cl client.Client, logger *zap.SugaredLogger) handle
 			seenSvcs.Add(nsname)
 		}
 
+		if o.GetName() == defaultProxyClass {
+			// For the default ProxyClass, we also need to reconcile all exposed
+			// Services that don't have an explicit ProxyClass set.
+			for _, matcher := range []client.ListOption{
+				client.MatchingFields{indexServiceExposed: "true"},
+				client.MatchingFields{indexServiceType: string(corev1.ServiceTypeLoadBalancer)},
+			} {
+				if err := cl.List(ctx, svcList, matcher); err != nil {
+					logger.Debugf("error listing exposed Services for ProxyClass: %v", err)
+					return nil
+				}
+
+				for _, svc := range svcList.Items {
+					if hasProxyClassAnnotation(&svc) {
+						continue
+					}
+					if !shouldExpose(&svc, isDefaultLoadBalancer) {
+						continue
+					}
+					nsname := fmt.Sprintf("%s/%s", svc.Namespace, svc.Name)
+					if seenSvcs.Contains(nsname) {
+						continue
+					}
+
+					reqs = append(reqs, reconcile.Request{NamespacedName: client.ObjectKeyFromObject(&svc)})
+					seenSvcs.Add(nsname)
+				}
+			}
+		}
+
 		return reqs
 	}
 }
diff --git a/cmd/k8s-operator/proxygroup.go b/cmd/k8s-operator/proxygroup.go
index 538933f14dbe1..4d5a795d79796 100644
--- a/cmd/k8s-operator/proxygroup.go
+++ b/cmd/k8s-operator/proxygroup.go
@@ -16,10 +16,12 @@ import (
 	"sort"
 	"strings"
 	"sync"
+	"time"
 
 	dockerref "github.com/distribution/reference"
 	"go.uber.org/zap"
 	xslices "golang.org/x/exp/slices"
+	"golang.org/x/time/rate"
 	appsv1 "k8s.io/api/apps/v1"
 	corev1 "k8s.io/api/core/v1"
 	rbacv1 "k8s.io/api/rbac/v1"
@@ -94,10 +96,12 @@ type ProxyGroupReconciler struct {
 	defaultProxyClass string
 	loginServer       string
 
-	mu                   sync.Mutex           // protects following
-	egressProxyGroups    set.Slice[types.UID] // for egress proxygroups gauge
-	ingressProxyGroups   set.Slice[types.UID] // for ingress proxygroups gauge
-	apiServerProxyGroups set.Slice[types.UID] // for kube-apiserver proxygroups gauge
+	mu                   sync.Mutex               // protects following
+	egressProxyGroups    set.Slice[types.UID]     // for egress proxygroups gauge
+	ingressProxyGroups   set.Slice[types.UID]     // for ingress proxygroups gauge
+	apiServerProxyGroups set.Slice[types.UID]     // for kube-apiserver proxygroups gauge
+	authKeyRateLimits    map[string]*rate.Limiter // per-ProxyGroup rate limiters for auth key re-issuance.
+	authKeyReissuing     map[string]bool
 }
 
 func (r *ProxyGroupReconciler) logger(name string) *zap.SugaredLogger {
@@ -294,7 +298,7 @@ func (r *ProxyGroupReconciler) validate(ctx context.Context, pg *tsapi.ProxyGrou
 func (r *ProxyGroupReconciler) maybeProvision(ctx context.Context, tailscaleClient tsClient, loginUrl string, pg *tsapi.ProxyGroup, proxyClass *tsapi.ProxyClass) (map[string][]netip.AddrPort, *notReadyReason, error) {
 	logger := r.logger(pg.Name)
 	r.mu.Lock()
-	r.ensureAddedToGaugeForProxyGroup(pg)
+	r.ensureStateAddedForProxyGroup(pg)
 	r.mu.Unlock()
 
 	svcToNodePorts := make(map[string]uint16)
@@ -629,13 +633,13 @@ func (r *ProxyGroupReconciler) cleanupDanglingResources(ctx context.Context, tai
 	}
 
 	for _, m := range metadata {
-		if m.ordinal+1 <= int(pgReplicas(pg)) {
+		if m.ordinal+1 <= pgReplicas(pg) {
 			continue
 		}
 
 		// Dangling resource, delete the config + state Secrets, as well as
 		// deleting the device from the tailnet.
-		if err := r.deleteTailnetDevice(ctx, tailscaleClient, m.tsID, logger); err != nil {
+		if err := r.ensureDeviceDeleted(ctx, tailscaleClient, m.tsID, logger); err != nil {
 			return err
 		}
 		if err := r.Delete(ctx, m.stateSecret); err != nil && !apierrors.IsNotFound(err) {
@@ -687,7 +691,7 @@ func (r *ProxyGroupReconciler) maybeCleanup(ctx context.Context, tailscaleClient
 	}
 
 	for _, m := range metadata {
-		if err := r.deleteTailnetDevice(ctx, tailscaleClient, m.tsID, logger); err != nil {
+		if err := r.ensureDeviceDeleted(ctx, tailscaleClient, m.tsID, logger); err != nil {
 			return false, err
 		}
 	}
@@ -703,12 +707,12 @@ func (r *ProxyGroupReconciler) maybeCleanup(ctx context.Context, tailscaleClient
 
 	logger.Infof("cleaned up ProxyGroup resources")
 	r.mu.Lock()
-	r.ensureRemovedFromGaugeForProxyGroup(pg)
+	r.ensureStateRemovedForProxyGroup(pg)
 	r.mu.Unlock()
 	return true, nil
 }
 
-func (r *ProxyGroupReconciler) deleteTailnetDevice(ctx context.Context, tailscaleClient tsClient, id tailcfg.StableNodeID, logger *zap.SugaredLogger) error {
+func (r *ProxyGroupReconciler) ensureDeviceDeleted(ctx context.Context, tailscaleClient tsClient, id tailcfg.StableNodeID, logger *zap.SugaredLogger) error {
 	logger.Debugf("deleting device %s from control", string(id))
 	if err := tailscaleClient.DeleteDevice(ctx, string(id)); err != nil {
 		if errResp, ok := errors.AsType[tailscale.ErrResponse](err); ok && errResp.Status == http.StatusNotFound {
@@ -734,6 +738,7 @@ func (r *ProxyGroupReconciler) ensureConfigSecretsCreated(
 	logger := r.logger(pg.Name)
 	endpoints = make(map[string][]netip.AddrPort, pgReplicas(pg)) // keyed by Service name.
 	for i := range pgReplicas(pg) {
+		logger = logger.With("Pod", fmt.Sprintf("%s-%d", pg.Name, i))
 		cfgSecret := &corev1.Secret{
 			ObjectMeta: metav1.ObjectMeta{
 				Name:            pgConfigSecretName(pg.Name, i),
@@ -751,38 +756,9 @@ func (r *ProxyGroupReconciler) ensureConfigSecretsCreated(
 			return nil, err
 		}
 
-		var authKey *string
-		if existingCfgSecret == nil {
-			logger.Debugf("Creating authkey for new ProxyGroup proxy")
-			tags := pg.Spec.Tags.Stringify()
-			if len(tags) == 0 {
-				tags = r.defaultTags
-			}
-			key, err := newAuthKey(ctx, tailscaleClient, tags)
-			if err != nil {
-				return nil, err
-			}
-			authKey = &key
-		}
-
-		if authKey == nil {
-			// Get state Secret to check if it's already authed.
-			stateSecret := &corev1.Secret{
-				ObjectMeta: metav1.ObjectMeta{
-					Name:      pgStateSecretName(pg.Name, i),
-					Namespace: r.tsNamespace,
-				},
-			}
-			if err = r.Get(ctx, client.ObjectKeyFromObject(stateSecret), stateSecret); err != nil && !apierrors.IsNotFound(err) {
-				return nil, err
-			}
-
-			if shouldRetainAuthKey(stateSecret) && existingCfgSecret != nil {
-				authKey, err = authKeyFromSecret(existingCfgSecret)
-				if err != nil {
-					return nil, fmt.Errorf("error retrieving auth key from existing config Secret: %w", err)
-				}
-			}
+		authKey, err := r.getAuthKey(ctx, tailscaleClient, pg, existingCfgSecret, i, logger)
+		if err != nil {
+			return nil, err
 		}
 
 		nodePortSvcName := pgNodePortServiceName(pg.Name, i)
@@ -918,11 +894,137 @@ func (r *ProxyGroupReconciler) ensureConfigSecretsCreated(
 				return nil, err
 			}
 		}
+
 	}
 
 	return endpoints, nil
 }
 
+// getAuthKey returns an auth key for the proxy, or nil if none is needed.
+// A new key is created if the config Secret doesn't exist yet, or if the
+// proxy has requested a reissue via its state Secret. An existing key is
+// retained while the device hasn't authed or a reissue is in progress.
+func (r *ProxyGroupReconciler) getAuthKey(ctx context.Context, tailscaleClient tsClient, pg *tsapi.ProxyGroup, existingCfgSecret *corev1.Secret, ordinal int32, logger *zap.SugaredLogger) (*string, error) {
+	// Get state Secret to check if it's already authed or has requested
+	// a fresh auth key.
+	stateSecret := &corev1.Secret{
+		ObjectMeta: metav1.ObjectMeta{
+			Name:      pgStateSecretName(pg.Name, ordinal),
+			Namespace: r.tsNamespace,
+		},
+	}
+	if err := r.Get(ctx, client.ObjectKeyFromObject(stateSecret), stateSecret); err != nil && !apierrors.IsNotFound(err) {
+		return nil, err
+	}
+
+	var createAuthKey bool
+	var cfgAuthKey *string
+	if existingCfgSecret == nil {
+		createAuthKey = true
+	} else {
+		var err error
+		cfgAuthKey, err = authKeyFromSecret(existingCfgSecret)
+		if err != nil {
+			return nil, fmt.Errorf("error retrieving auth key from existing config Secret: %w", err)
+		}
+	}
+
+	if !createAuthKey {
+		var err error
+		createAuthKey, err = r.shouldReissueAuthKey(ctx, tailscaleClient, pg, stateSecret, cfgAuthKey)
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	var authKey *string
+	if createAuthKey {
+		logger.Debugf("creating auth key for ProxyGroup proxy %q", stateSecret.Name)
+
+		tags := pg.Spec.Tags.Stringify()
+		if len(tags) == 0 {
+			tags = r.defaultTags
+		}
+		key, err := newAuthKey(ctx, tailscaleClient, tags)
+		if err != nil {
+			return nil, err
+		}
+		authKey = &key
+	} else {
+		// Retain auth key if the device hasn't authed yet, or if a
+		// reissue is in progress (device_id is stale during reissue).
+		_, reissueRequested := stateSecret.Data[kubetypes.KeyReissueAuthkey]
+		if !deviceAuthed(stateSecret) || reissueRequested {
+			authKey = cfgAuthKey
+		}
+	}
+
+	return authKey, nil
+}
+
+// shouldReissueAuthKey returns true if the proxy needs a new auth key. It
+// tracks in-flight reissues via authKeyReissuing to avoid duplicate API calls
+// across reconciles.
+func (r *ProxyGroupReconciler) shouldReissueAuthKey(ctx context.Context, tailscaleClient tsClient, pg *tsapi.ProxyGroup, stateSecret *corev1.Secret, cfgAuthKey *string) (shouldReissue bool, err error) {
+	r.mu.Lock()
+	reissuing := r.authKeyReissuing[stateSecret.Name]
+	r.mu.Unlock()
+
+	if reissuing {
+		// Check if reissue is complete by seeing if request was cleared
+		_, requestStillPresent := stateSecret.Data[kubetypes.KeyReissueAuthkey]
+		if !requestStillPresent {
+			// Containerboot cleared the request, reissue is complete
+			r.mu.Lock()
+			r.authKeyReissuing[stateSecret.Name] = false
+			r.mu.Unlock()
+			r.log.Debugf("auth key reissue completed for %q", stateSecret.Name)
+			return false, nil
+		}
+
+		// Reissue still in-flight; waiting for containerboot to pick up new key
+		r.log.Debugf("auth key already in process of re-issuance, waiting for secret to be updated")
+		return false, nil
+	}
+
+	defer func() {
+		r.mu.Lock()
+		r.authKeyReissuing[stateSecret.Name] = shouldReissue
+		r.mu.Unlock()
+	}()
+
+	brokenAuthkey, ok := stateSecret.Data[kubetypes.KeyReissueAuthkey]
+	if !ok {
+		// reissue hasn't been requested since the key in the secret hasn't been populated
+		return false, nil
+	}
+
+	empty := cfgAuthKey == nil || *cfgAuthKey == ""
+	broken := cfgAuthKey != nil && *cfgAuthKey == string(brokenAuthkey)
+
+	// A new key has been written but the proxy hasn't picked it up yet.
+	if !empty && !broken {
+		return false, nil
+	}
+
+	lim := r.authKeyRateLimits[pg.Name]
+	if !lim.Allow() {
+		r.log.Debugf("auth key re-issuance rate limit exceeded, limit: %.2f, burst: %d, tokens: %.2f",
+			lim.Limit(), lim.Burst(), lim.Tokens())
+		return false, fmt.Errorf("auth key re-issuance rate limit exceeded for ProxyGroup %q, will retry with backoff", pg.Name)
+	}
+
+	r.log.Infof("Proxy failing to auth; attempting cleanup and new key")
+	if tsID := stateSecret.Data[kubetypes.KeyDeviceID]; len(tsID) > 0 {
+		id := tailcfg.StableNodeID(tsID)
+		if err := r.ensureDeviceDeleted(ctx, tailscaleClient, id, r.log); err != nil {
+			return false, err
+		}
+	}
+
+	return true, nil
+}
+
 type FindStaticEndpointErr struct {
 	msg string
 }
@@ -1016,9 +1118,9 @@ func getStaticEndpointAddress(a *corev1.NodeAddress, port uint16) *netip.AddrPor
 	return new(netip.AddrPortFrom(addr, port))
 }
 
-// ensureAddedToGaugeForProxyGroup ensures the gauge metric for the ProxyGroup resource is updated when the ProxyGroup
-// is created. r.mu must be held.
-func (r *ProxyGroupReconciler) ensureAddedToGaugeForProxyGroup(pg *tsapi.ProxyGroup) {
+// ensureStateAddedForProxyGroup ensures the gauge metric for the ProxyGroup resource is updated when the ProxyGroup
+// is created, and initialises per-ProxyGroup rate limits on re-issuing auth keys. r.mu must be held.
+func (r *ProxyGroupReconciler) ensureStateAddedForProxyGroup(pg *tsapi.ProxyGroup) {
 	switch pg.Spec.Type {
 	case tsapi.ProxyGroupTypeEgress:
 		r.egressProxyGroups.Add(pg.UID)
@@ -1030,11 +1132,24 @@ func (r *ProxyGroupReconciler) ensureAddedToGaugeForProxyGroup(pg *tsapi.ProxyGr
 	gaugeEgressProxyGroupResources.Set(int64(r.egressProxyGroups.Len()))
 	gaugeIngressProxyGroupResources.Set(int64(r.ingressProxyGroups.Len()))
 	gaugeAPIServerProxyGroupResources.Set(int64(r.apiServerProxyGroups.Len()))
+
+	if _, ok := r.authKeyRateLimits[pg.Name]; !ok {
+		// Allow every replica to have its auth key re-issued quickly the first
+		// time, but with an overall limit of 1 every 30s after a burst.
+		r.authKeyRateLimits[pg.Name] = rate.NewLimiter(rate.Every(30*time.Second), int(pgReplicas(pg)))
+	}
+
+	for i := range pgReplicas(pg) {
+		rep := pgStateSecretName(pg.Name, i)
+		if _, ok := r.authKeyReissuing[rep]; !ok {
+			r.authKeyReissuing[rep] = false
+		}
+	}
 }
 
-// ensureRemovedFromGaugeForProxyGroup ensures the gauge metric for the ProxyGroup resource type is updated when the
-// ProxyGroup is deleted. r.mu must be held.
-func (r *ProxyGroupReconciler) ensureRemovedFromGaugeForProxyGroup(pg *tsapi.ProxyGroup) {
+// ensureStateRemovedForProxyGroup ensures the gauge metric for the ProxyGroup resource type is updated when the
+// ProxyGroup is deleted, and deletes the per-ProxyGroup rate limiter to free memory. r.mu must be held.
+func (r *ProxyGroupReconciler) ensureStateRemovedForProxyGroup(pg *tsapi.ProxyGroup) {
 	switch pg.Spec.Type {
 	case tsapi.ProxyGroupTypeEgress:
 		r.egressProxyGroups.Remove(pg.UID)
@@ -1046,6 +1161,7 @@ func (r *ProxyGroupReconciler) ensureRemovedFromGaugeForProxyGroup(pg *tsapi.Pro
 	gaugeEgressProxyGroupResources.Set(int64(r.egressProxyGroups.Len()))
 	gaugeIngressProxyGroupResources.Set(int64(r.ingressProxyGroups.Len()))
 	gaugeAPIServerProxyGroupResources.Set(int64(r.apiServerProxyGroups.Len()))
+	delete(r.authKeyRateLimits, pg.Name)
 }
 
 func pgTailscaledConfig(pg *tsapi.ProxyGroup, loginServer string, pc *tsapi.ProxyClass, idx int32, authKey *string, staticEndpoints []netip.AddrPort, oldAdvertiseServices []string) (tailscaledConfigs, error) {
@@ -1106,7 +1222,7 @@ func getNodeMetadata(ctx context.Context, pg *tsapi.ProxyGroup, cl client.Client
 		return nil, fmt.Errorf("failed to list state Secrets: %w", err)
 	}
 	for _, secret := range secrets.Items {
-		var ordinal int
+		var ordinal int32
 		if _, err := fmt.Sscanf(secret.Name, pg.Name+"-%d", &ordinal); err != nil {
 			return nil, fmt.Errorf("unexpected secret %s was labelled as owned by the ProxyGroup %s: %w", secret.Name, pg.Name, err)
 		}
@@ -1213,7 +1329,7 @@ func (r *ProxyGroupReconciler) getClientAndLoginURL(ctx context.Context, tailnet
 }
 
 type nodeMetadata struct {
-	ordinal     int
+	ordinal     int32
 	stateSecret *corev1.Secret
 	podUID      string // or empty if the Pod no longer exists.
 	tsID        tailcfg.StableNodeID
diff --git a/cmd/k8s-operator/proxygroup_test.go b/cmd/k8s-operator/proxygroup_test.go
index 9b3ee0e0fd30f..1a50ee1f05f44 100644
--- a/cmd/k8s-operator/proxygroup_test.go
+++ b/cmd/k8s-operator/proxygroup_test.go
@@ -6,15 +6,19 @@
 package main
 
 import (
+	"context"
 	"encoding/json"
 	"fmt"
 	"net/netip"
+	"reflect"
 	"slices"
+	"strings"
 	"testing"
 	"time"
 
 	"github.com/google/go-cmp/cmp"
 	"go.uber.org/zap"
+	"golang.org/x/time/rate"
 	appsv1 "k8s.io/api/apps/v1"
 	corev1 "k8s.io/api/core/v1"
 	rbacv1 "k8s.io/api/rbac/v1"
@@ -28,7 +32,6 @@ import (
 	"sigs.k8s.io/controller-runtime/pkg/client/fake"
 	"tailscale.com/client/tailscale"
 	"tailscale.com/ipn"
-	kube "tailscale.com/k8s-operator"
 	tsoperator "tailscale.com/k8s-operator"
 	tsapi "tailscale.com/k8s-operator/apis/v1alpha1"
 	"tailscale.com/kube/k8s-proxy/conf"
@@ -637,10 +640,12 @@ func TestProxyGroupWithStaticEndpoints(t *testing.T) {
 				tsFirewallMode:    "auto",
 				defaultProxyClass: "default-pc",
 
-				Client:   fc,
-				tsClient: tsClient,
-				recorder: fr,
-				clock:    cl,
+				Client:            fc,
+				tsClient:          tsClient,
+				recorder:          fr,
+				clock:             cl,
+				authKeyRateLimits: make(map[string]*rate.Limiter),
+				authKeyReissuing:  make(map[string]bool),
 			}
 
 			for i, r := range tt.reconciles {
@@ -780,11 +785,13 @@ func TestProxyGroupWithStaticEndpoints(t *testing.T) {
 					tsFirewallMode:    "auto",
 					defaultProxyClass: "default-pc",
 
-					Client:   fc,
-					tsClient: tsClient,
-					recorder: fr,
-					log:      zl.Sugar().With("TestName", tt.name).With("Reconcile", "cleanup"),
-					clock:    cl,
+					Client:            fc,
+					tsClient:          tsClient,
+					recorder:          fr,
+					log:               zl.Sugar().With("TestName", tt.name).With("Reconcile", "cleanup"),
+					clock:             cl,
+					authKeyRateLimits: make(map[string]*rate.Limiter),
+					authKeyReissuing:  make(map[string]bool),
 				}
 
 				if err := fc.Delete(t.Context(), pg); err != nil {
@@ -841,12 +848,15 @@ func TestProxyGroup(t *testing.T) {
 		tsFirewallMode:    "auto",
 		defaultProxyClass: "default-pc",
 
-		Client:   fc,
-		tsClient: tsClient,
-		recorder: fr,
-		log:      zl.Sugar(),
-		clock:    cl,
+		Client:            fc,
+		tsClient:          tsClient,
+		recorder:          fr,
+		log:               zl.Sugar(),
+		clock:             cl,
+		authKeyRateLimits: make(map[string]*rate.Limiter),
+		authKeyReissuing:  make(map[string]bool),
 	}
+
 	crd := &apiextensionsv1.CustomResourceDefinition{ObjectMeta: metav1.ObjectMeta{Name: serviceMonitorCRD}}
 	opts := configOpts{
 		proxyType:          "proxygroup",
@@ -863,7 +873,7 @@ func TestProxyGroup(t *testing.T) {
 		tsoperator.SetProxyGroupCondition(pg, tsapi.ProxyGroupReady, metav1.ConditionFalse, reasonProxyGroupCreating, "the ProxyGroup's ProxyClass \"default-pc\" is not yet in a ready state, waiting...", 1, cl, zl.Sugar())
 		expectEqual(t, fc, pg)
 		expectProxyGroupResources(t, fc, pg, false, pc)
-		if kube.ProxyGroupAvailable(pg) {
+		if tsoperator.ProxyGroupAvailable(pg) {
 			t.Fatal("expected ProxyGroup to not be available")
 		}
 	})
@@ -891,7 +901,7 @@ func TestProxyGroup(t *testing.T) {
 		tsoperator.SetProxyGroupCondition(pg, tsapi.ProxyGroupAvailable, metav1.ConditionFalse, reasonProxyGroupCreating, "0/2 ProxyGroup pods running", 0, cl, zl.Sugar())
 		expectEqual(t, fc, pg)
 		expectProxyGroupResources(t, fc, pg, true, pc)
-		if kube.ProxyGroupAvailable(pg) {
+		if tsoperator.ProxyGroupAvailable(pg) {
 			t.Fatal("expected ProxyGroup to not be available")
 		}
 		if expected := 1; reconciler.egressProxyGroups.Len() != expected {
@@ -935,7 +945,7 @@ func TestProxyGroup(t *testing.T) {
 		tsoperator.SetProxyGroupCondition(pg, tsapi.ProxyGroupAvailable, metav1.ConditionTrue, reasonProxyGroupAvailable, "2/2 ProxyGroup pods running", 0, cl, zl.Sugar())
 		expectEqual(t, fc, pg)
 		expectProxyGroupResources(t, fc, pg, true, pc)
-		if !kube.ProxyGroupAvailable(pg) {
+		if !tsoperator.ProxyGroupAvailable(pg) {
 			t.Fatal("expected ProxyGroup to be available")
 		}
 	})
@@ -1045,12 +1055,14 @@ func TestProxyGroupTypes(t *testing.T) {
 
 	zl, _ := zap.NewDevelopment()
 	reconciler := &ProxyGroupReconciler{
-		tsNamespace:  tsNamespace,
-		tsProxyImage: testProxyImage,
-		Client:       fc,
-		log:          zl.Sugar(),
-		tsClient:     &fakeTSClient{},
-		clock:        tstest.NewClock(tstest.ClockOpts{}),
+		tsNamespace:       tsNamespace,
+		tsProxyImage:      testProxyImage,
+		Client:            fc,
+		log:               zl.Sugar(),
+		tsClient:          &fakeTSClient{},
+		clock:             tstest.NewClock(tstest.ClockOpts{}),
+		authKeyRateLimits: make(map[string]*rate.Limiter),
+		authKeyReissuing:  make(map[string]bool),
 	}
 
 	t.Run("egress_type", func(t *testing.T) {
@@ -1285,12 +1297,14 @@ func TestKubeAPIServerStatusConditionFlow(t *testing.T) {
 		WithStatusSubresource(pg).
 		Build()
 	r := &ProxyGroupReconciler{
-		tsNamespace:  tsNamespace,
-		tsProxyImage: testProxyImage,
-		Client:       fc,
-		log:          zap.Must(zap.NewDevelopment()).Sugar(),
-		tsClient:     &fakeTSClient{},
-		clock:        tstest.NewClock(tstest.ClockOpts{}),
+		tsNamespace:       tsNamespace,
+		tsProxyImage:      testProxyImage,
+		Client:            fc,
+		log:               zap.Must(zap.NewDevelopment()).Sugar(),
+		tsClient:          &fakeTSClient{},
+		clock:             tstest.NewClock(tstest.ClockOpts{}),
+		authKeyRateLimits: make(map[string]*rate.Limiter),
+		authKeyReissuing:  make(map[string]bool),
 	}
 
 	expectReconciled(t, r, "", pg.Name)
@@ -1338,12 +1352,14 @@ func TestKubeAPIServerType_DoesNotOverwriteServicesConfig(t *testing.T) {
 		Build()
 
 	reconciler := &ProxyGroupReconciler{
-		tsNamespace:  tsNamespace,
-		tsProxyImage: testProxyImage,
-		Client:       fc,
-		log:          zap.Must(zap.NewDevelopment()).Sugar(),
-		tsClient:     &fakeTSClient{},
-		clock:        tstest.NewClock(tstest.ClockOpts{}),
+		tsNamespace:       tsNamespace,
+		tsProxyImage:      testProxyImage,
+		Client:            fc,
+		log:               zap.Must(zap.NewDevelopment()).Sugar(),
+		tsClient:          &fakeTSClient{},
+		clock:             tstest.NewClock(tstest.ClockOpts{}),
+		authKeyRateLimits: make(map[string]*rate.Limiter),
+		authKeyReissuing:  make(map[string]bool),
 	}
 
 	pg := &tsapi.ProxyGroup{
@@ -1367,7 +1383,7 @@ func TestKubeAPIServerType_DoesNotOverwriteServicesConfig(t *testing.T) {
 	cfg := conf.VersionedConfig{
 		Version: "v1alpha1",
 		ConfigV1Alpha1: &conf.ConfigV1Alpha1{
-			AuthKey:  new("secret-authkey"),
+			AuthKey:  new("new-authkey"),
 			State:    new(fmt.Sprintf("kube:%s", pgPodName(pg.Name, 0))),
 			App:      new(kubetypes.AppProxyGroupKubeAPIServer),
 			LogLevel: new("debug"),
@@ -1423,12 +1439,14 @@ func TestIngressAdvertiseServicesConfigPreserved(t *testing.T) {
 		WithStatusSubresource(&tsapi.ProxyGroup{}).
 		Build()
 	reconciler := &ProxyGroupReconciler{
-		tsNamespace:  tsNamespace,
-		tsProxyImage: testProxyImage,
-		Client:       fc,
-		log:          zap.Must(zap.NewDevelopment()).Sugar(),
-		tsClient:     &fakeTSClient{},
-		clock:        tstest.NewClock(tstest.ClockOpts{}),
+		tsNamespace:       tsNamespace,
+		tsProxyImage:      testProxyImage,
+		Client:            fc,
+		log:               zap.Must(zap.NewDevelopment()).Sugar(),
+		tsClient:          &fakeTSClient{},
+		clock:             tstest.NewClock(tstest.ClockOpts{}),
+		authKeyRateLimits: make(map[string]*rate.Limiter),
+		authKeyReissuing:  make(map[string]bool),
 	}
 
 	existingServices := []string{"svc1", "svc2"}
@@ -1653,6 +1671,197 @@ func TestValidateProxyGroup(t *testing.T) {
 	}
 }
 
+func TestProxyGroupGetAuthKey(t *testing.T) {
+	pg := &tsapi.ProxyGroup{
+		ObjectMeta: metav1.ObjectMeta{
+			Name:       "test",
+			Finalizers: []string{"tailscale.com/finalizer"},
+		},
+		Spec: tsapi.ProxyGroupSpec{
+			Type:     tsapi.ProxyGroupTypeEgress,
+			Replicas: new(int32(1)),
+		},
+	}
+	tsClient := &fakeTSClient{}
+
+	// Variables to reference in test cases.
+	existingAuthKey := new("existing-auth-key")
+	newAuthKey := new("new-authkey")
+	configWith := func(authKey *string) map[string][]byte {
+		value := []byte("{}")
+		if authKey != nil {
+			value = fmt.Appendf(nil, `{"AuthKey": "%s"}`, *authKey)
+		}
+		return map[string][]byte{
+			tsoperator.TailscaledConfigFileName(pgMinCapabilityVersion): value,
+		}
+	}
+
+	initTest := func() (*ProxyGroupReconciler, client.WithWatch) {
+		fc := fake.NewClientBuilder().
+			WithScheme(tsapi.GlobalScheme).
+			WithObjects(pg).
+			WithStatusSubresource(pg).
+			Build()
+		zl, _ := zap.NewDevelopment()
+		fr := record.NewFakeRecorder(1)
+		cl := tstest.NewClock(tstest.ClockOpts{})
+		reconciler := &ProxyGroupReconciler{
+			tsNamespace:    tsNamespace,
+			tsProxyImage:   testProxyImage,
+			defaultTags:    []string{"tag:test-tag"},
+			tsFirewallMode: "auto",
+
+			Client:            fc,
+			tsClient:          tsClient,
+			recorder:          fr,
+			log:               zl.Sugar(),
+			clock:             cl,
+			authKeyRateLimits: make(map[string]*rate.Limiter),
+			authKeyReissuing:  make(map[string]bool),
+		}
+		reconciler.ensureStateAddedForProxyGroup(pg)
+
+		return reconciler, fc
+	}
+
+	// Config Secret: exists or not, has key or not.
+	// State Secret: has device ID or not, requested reissue or not.
+	for name, tc := range map[string]struct {
+		configData      map[string][]byte
+		stateData       map[string][]byte
+		expectedAuthKey *string
+		expectReissue   bool
+	}{
+		"no_secrets_needs_new": {
+			expectedAuthKey: newAuthKey, // New ProxyGroup or manually cleared Pod.
+		},
+		"no_config_secret_state_authed_ok": {
+			stateData: map[string][]byte{
+				kubetypes.KeyDeviceID: []byte("nodeid-0"),
+			},
+			expectedAuthKey: newAuthKey, // Always create an auth key if we're creating the config Secret.
+		},
+		"config_secret_without_key_state_authed_with_reissue_needs_new": {
+			configData: configWith(nil),
+			stateData: map[string][]byte{
+				kubetypes.KeyDeviceID:       []byte("nodeid-0"),
+				kubetypes.KeyReissueAuthkey: []byte(""),
+			},
+			expectedAuthKey: newAuthKey,
+			expectReissue:   true, // Device is authed but reissue was requested.
+		},
+		"config_secret_with_key_state_with_reissue_stale_ok": {
+			configData: configWith(existingAuthKey),
+			stateData: map[string][]byte{
+				kubetypes.KeyReissueAuthkey: []byte("some-older-authkey"),
+			},
+			expectedAuthKey: existingAuthKey, // Config's auth key is different from the one marked for reissue.
+		},
+		"config_secret_with_key_state_with_reissue_existing_key_needs_new": {
+			configData: configWith(existingAuthKey),
+			stateData: map[string][]byte{
+				kubetypes.KeyDeviceID:       []byte("nodeid-0"),
+				kubetypes.KeyReissueAuthkey: []byte(*existingAuthKey),
+			},
+			expectedAuthKey: newAuthKey,
+			expectReissue:   true, // Current config's auth key is marked for reissue.
+		},
+		"config_secret_without_key_no_state_ok": {
+			configData:      configWith(nil),
+			expectedAuthKey: nil, // Proxy will set reissue_authkey and then next reconcile will reissue.
+		},
+		"config_secret_without_key_state_authed_ok": {
+			configData: configWith(nil),
+			stateData: map[string][]byte{
+				kubetypes.KeyDeviceID: []byte("nodeid-0"),
+			},
+			expectedAuthKey: nil, // Device is already authed.
+		},
+		"config_secret_with_key_state_authed_ok": {
+			configData: configWith(existingAuthKey),
+			stateData: map[string][]byte{
+				kubetypes.KeyDeviceID: []byte("nodeid-0"),
+			},
+			expectedAuthKey: nil, // Auth key getting removed because device is authed.
+		},
+		"config_secret_with_key_no_state_keeps_existing": {
+			configData:      configWith(existingAuthKey),
+			expectedAuthKey: existingAuthKey, // No state, waiting for containerboot to try the auth key.
+		},
+	} {
+		t.Run(name, func(t *testing.T) {
+			tsClient.deleted = tsClient.deleted[:0] // Reset deleted devices for each test case.
+			reconciler, fc := initTest()
+			var cfgSecret *corev1.Secret
+			if tc.configData != nil {
+				cfgSecret = &corev1.Secret{
+					ObjectMeta: metav1.ObjectMeta{
+						Name:      pgConfigSecretName(pg.Name, 0),
+						Namespace: tsNamespace,
+					},
+					Data: tc.configData,
+				}
+			}
+			if tc.stateData != nil {
+				mustCreate(t, fc, &corev1.Secret{
+					ObjectMeta: metav1.ObjectMeta{
+						Name:      pgStateSecretName(pg.Name, 0),
+						Namespace: tsNamespace,
+					},
+					Data: tc.stateData,
+				})
+			}
+
+			authKey, err := reconciler.getAuthKey(t.Context(), tsClient, pg, cfgSecret, 0, reconciler.log.With("TestName", t.Name()))
+			if err != nil {
+				t.Fatalf("unexpected error getting auth key: %v", err)
+			}
+			if !reflect.DeepEqual(authKey, tc.expectedAuthKey) {
+				deref := func(s *string) string {
+					if s == nil {
+						return "<nil>"
+					}
+					return *s
+				}
+				t.Errorf("expected auth key %v, got %v", deref(tc.expectedAuthKey), deref(authKey))
+			}
+
+			// Use the device deletion as a proxy for the fact the new auth key
+			// was due to a reissue.
+			switch {
+			case tc.expectReissue && len(tsClient.deleted) != 1:
+				t.Errorf("expected 1 deleted device, got %v", tsClient.deleted)
+			case !tc.expectReissue && len(tsClient.deleted) != 0:
+				t.Errorf("expected no deleted devices, got %v", tsClient.deleted)
+			}
+
+			if tc.expectReissue {
+				// Trigger the rate limit in a tight loop. Up to 100 iterations
+				// to allow for CI that is extremely slow, but should happen on
+				// first try for any reasonable machine.
+				stateSecretName := pgStateSecretName(pg.Name, 0)
+				for range 100 {
+					//NOTE: (ChaosInTheCRD) we added some protection here to avoid
+					// trying to reissue when already reissung. This overrides it.
+					reconciler.mu.Lock()
+					reconciler.authKeyReissuing[stateSecretName] = false
+					reconciler.mu.Unlock()
+					_, err := reconciler.getAuthKey(context.Background(), tsClient, pg, cfgSecret, 0,
+						reconciler.log.With("TestName", t.Name()))
+					if err != nil {
+						if !strings.Contains(err.Error(), "rate limit exceeded") {
+							t.Fatalf("unexpected error getting auth key: %v", err)
+						}
+						return // Expected rate limit error.
+					}
+				}
+				t.Fatal("expected rate limit error, but got none")
+			}
+		})
+	}
+}
+
 func proxyClassesForLEStagingTest() (*tsapi.ProxyClass, *tsapi.ProxyClass, *tsapi.ProxyClass) {
 	pcLEStaging := &tsapi.ProxyClass{
 		ObjectMeta: metav1.ObjectMeta{
@@ -1903,6 +2112,8 @@ func TestProxyGroupLetsEncryptStaging(t *testing.T) {
 				tsClient:          &fakeTSClient{},
 				log:               zl.Sugar(),
 				clock:             cl,
+				authKeyRateLimits: make(map[string]*rate.Limiter),
+				authKeyReissuing:  make(map[string]bool),
 			}
 
 			expectReconciled(t, reconciler, "", pg.Name)
diff --git a/cmd/k8s-operator/sts.go b/cmd/k8s-operator/sts.go
index 5f33a94905785..519f81fe0db29 100644
--- a/cmd/k8s-operator/sts.go
+++ b/cmd/k8s-operator/sts.go
@@ -1111,7 +1111,7 @@ func tailscaledConfig(stsC *tailscaleSTSConfig, loginUrl string, newAuthkey stri
 
 	if newAuthkey != "" {
 		conf.AuthKey = &newAuthkey
-	} else if shouldRetainAuthKey(oldSecret) {
+	} else if !deviceAuthed(oldSecret) {
 		key, err := authKeyFromSecret(oldSecret)
 		if err != nil {
 			return nil, fmt.Errorf("error retrieving auth key from Secret: %w", err)
@@ -1164,6 +1164,8 @@ func latestConfigFromSecret(s *corev1.Secret) (*ipn.ConfigVAlpha, error) {
 	return conf, nil
 }
 
+// authKeyFromSecret returns the auth key from the latest config version if
+// found, or else nil.
 func authKeyFromSecret(s *corev1.Secret) (key *string, err error) {
 	conf, err := latestConfigFromSecret(s)
 	if err != nil {
@@ -1180,13 +1182,13 @@ func authKeyFromSecret(s *corev1.Secret) (key *string, err error) {
 	return key, nil
 }
 
-// shouldRetainAuthKey returns true if the state stored in a proxy's state Secret suggests that auth key should be
-// retained (because the proxy has not yet successfully authenticated).
-func shouldRetainAuthKey(s *corev1.Secret) bool {
+// deviceAuthed returns true if the state stored in a proxy's state Secret
+// suggests that the proxy has successfully authenticated.
+func deviceAuthed(s *corev1.Secret) bool {
 	if s == nil {
-		return false // nothing to retain here
+		return false // No state Secret means no device state.
 	}
-	return len(s.Data["device_id"]) == 0 // proxy has not authed yet
+	return len(s.Data["device_id"]) > 0
 }
 
 func shouldAcceptRoutes(pc *tsapi.ProxyClass) bool {
diff --git a/cmd/k8s-operator/svc.go b/cmd/k8s-operator/svc.go
index 31be22aa12ca3..6f12148c85807 100644
--- a/cmd/k8s-operator/svc.go
+++ b/cmd/k8s-operator/svc.go
@@ -42,8 +42,6 @@ const (
 	reasonProxyInvalid = "ProxyInvalid"
 	reasonProxyFailed  = "ProxyFailed"
 	reasonProxyPending = "ProxyPending"
-
-	indexServiceProxyClass = ".metadata.annotations.service-proxy-class"
 )
 
 type ServiceReconciler struct {
@@ -97,7 +95,7 @@ func childResourceLabels(name, ns, typ string) map[string]string {
 func (a *ServiceReconciler) isTailscaleService(svc *corev1.Service) bool {
 	targetIP := tailnetTargetAnnotation(svc)
 	targetFQDN := svc.Annotations[AnnotationTailnetTargetFQDN]
-	return a.shouldExpose(svc) || targetIP != "" || targetFQDN != ""
+	return shouldExpose(svc, a.isDefaultLoadBalancer) || targetIP != "" || targetFQDN != ""
 }
 
 func (a *ServiceReconciler) Reconcile(ctx context.Context, req reconcile.Request) (_ reconcile.Result, err error) {
@@ -164,7 +162,7 @@ func (a *ServiceReconciler) maybeCleanup(ctx context.Context, logger *zap.Sugare
 	}
 
 	proxyTyp := proxyTypeEgress
-	if a.shouldExpose(svc) {
+	if shouldExpose(svc, a.isDefaultLoadBalancer) {
 		proxyTyp = proxyTypeIngressService
 	}
 
@@ -275,16 +273,16 @@ func (a *ServiceReconciler) maybeProvision(ctx context.Context, logger *zap.Suga
 		LoginServer:         a.ssr.loginServer,
 	}
 	sts.proxyType = proxyTypeEgress
-	if a.shouldExpose(svc) {
+	if shouldExpose(svc, a.isDefaultLoadBalancer) {
 		sts.proxyType = proxyTypeIngressService
 	}
 
 	a.mu.Lock()
-	if a.shouldExposeClusterIP(svc) {
+	if shouldExposeClusterIP(svc, a.isDefaultLoadBalancer) {
 		sts.ClusterTargetIP = svc.Spec.ClusterIP
 		a.managedIngressProxies.Add(svc.UID)
 		gaugeIngressProxies.Set(int64(a.managedIngressProxies.Len()))
-	} else if a.shouldExposeDNSName(svc) {
+	} else if shouldExposeDNSName(svc) {
 		sts.ClusterTargetDNSName = svc.Spec.ExternalName
 		a.managedIngressProxies.Add(svc.UID)
 		gaugeIngressProxies.Set(int64(a.managedIngressProxies.Len()))
@@ -410,19 +408,19 @@ func validateService(svc *corev1.Service) []string {
 	return violations
 }
 
-func (a *ServiceReconciler) shouldExpose(svc *corev1.Service) bool {
-	return a.shouldExposeClusterIP(svc) || a.shouldExposeDNSName(svc)
+func shouldExpose(svc *corev1.Service, isDefaultLoadBalancer bool) bool {
+	return shouldExposeClusterIP(svc, isDefaultLoadBalancer) || shouldExposeDNSName(svc)
 }
 
-func (a *ServiceReconciler) shouldExposeDNSName(svc *corev1.Service) bool {
+func shouldExposeDNSName(svc *corev1.Service) bool {
 	return hasExposeAnnotation(svc) && svc.Spec.Type == corev1.ServiceTypeExternalName && svc.Spec.ExternalName != ""
 }
 
-func (a *ServiceReconciler) shouldExposeClusterIP(svc *corev1.Service) bool {
+func shouldExposeClusterIP(svc *corev1.Service, isDefaultLoadBalancer bool) bool {
 	if svc.Spec.ClusterIP == "" {
 		return false
 	}
-	return isTailscaleLoadBalancerService(svc, a.isDefaultLoadBalancer) || hasExposeAnnotation(svc)
+	return isTailscaleLoadBalancerService(svc, isDefaultLoadBalancer) || hasExposeAnnotation(svc)
 }
 
 func isTailscaleLoadBalancerService(svc *corev1.Service, isDefaultLoadBalancer bool) bool {
diff --git a/cmd/k8s-operator/svc_test.go b/cmd/k8s-operator/svc_test.go
new file mode 100644
index 0000000000000..3a6ea044d5af5
--- /dev/null
+++ b/cmd/k8s-operator/svc_test.go
@@ -0,0 +1,221 @@
+// Copyright (c) Tailscale Inc & contributors
+// SPDX-License-Identifier: BSD-3-Clause
+
+//go:build !plan9
+
+package main
+
+import (
+	"context"
+	"slices"
+	"testing"
+
+	"go.uber.org/zap"
+	corev1 "k8s.io/api/core/v1"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/apimachinery/pkg/types"
+	"sigs.k8s.io/controller-runtime/pkg/client/fake"
+	"sigs.k8s.io/controller-runtime/pkg/reconcile"
+	tsapi "tailscale.com/k8s-operator/apis/v1alpha1"
+	"tailscale.com/kube/kubetypes"
+	"tailscale.com/tstest"
+)
+
+func TestService_DefaultProxyClassInitiallyNotReady(t *testing.T) {
+	pc := &tsapi.ProxyClass{
+		ObjectMeta: metav1.ObjectMeta{Name: "custom-metadata"},
+		Spec: tsapi.ProxyClassSpec{
+			TailscaleConfig: &tsapi.TailscaleConfig{
+				AcceptRoutes: true,
+			},
+			StatefulSet: &tsapi.StatefulSet{
+				Labels:      tsapi.Labels{"foo": "bar"},
+				Annotations: map[string]string{"bar.io/foo": "some-val"},
+				Pod:         &tsapi.Pod{Annotations: map[string]string{"foo.io/bar": "some-val"}},
+			},
+		},
+	}
+	fc := fake.NewClientBuilder().
+		WithScheme(tsapi.GlobalScheme).
+		WithObjects(pc).
+		WithStatusSubresource(pc).
+		Build()
+	ft := &fakeTSClient{}
+	zl := zap.Must(zap.NewDevelopment())
+	clock := tstest.NewClock(tstest.ClockOpts{})
+	sr := &ServiceReconciler{
+		Client: fc,
+		ssr: &tailscaleSTSReconciler{
+			Client:            fc,
+			tsClient:          ft,
+			defaultTags:       []string{"tag:k8s"},
+			operatorNamespace: "operator-ns",
+			proxyImage:        "tailscale/tailscale",
+		},
+		defaultProxyClass: "custom-metadata",
+		logger:            zl.Sugar(),
+		clock:             clock,
+	}
+
+	// 1. A new tailscale LoadBalancer Service is created but the default
+	// ProxyClass is not ready yet.
+	mustCreate(t, fc, &corev1.Service{
+		ObjectMeta: metav1.ObjectMeta{
+			Name:      "test",
+			Namespace: "default",
+			// The apiserver is supposed to set the UID, but the fake client
+			// doesn't. So, set it explicitly because other code later depends
+			// on it being set.
+			UID: types.UID("1234-UID"),
+		},
+		Spec: corev1.ServiceSpec{
+			ClusterIP:         "10.20.30.40",
+			Type:              corev1.ServiceTypeLoadBalancer,
+			LoadBalancerClass: new("tailscale"),
+		},
+	})
+	expectReconciled(t, sr, "default", "test")
+	labels := map[string]string{
+		kubetypes.LabelManaged: "true",
+		LabelParentName:        "test",
+		LabelParentNamespace:   "operator-ns",
+		LabelParentType:        "svc",
+	}
+	s, err := getSingleObject[corev1.Secret](context.Background(), fc, "operator-ns", labels)
+	if err != nil {
+		t.Fatalf("finding Secret for %q: %v", "test", err)
+	}
+	if s != nil {
+		t.Fatalf("expected no Secret to be created when default ProxyClass is not ready, but found one: %v", s)
+	}
+
+	// 2. ProxyClass is set to Ready, the Service can become ready now.
+	mustUpdateStatus(t, fc, "", "custom-metadata", func(pc *tsapi.ProxyClass) {
+		pc.Status = tsapi.ProxyClassStatus{
+			Conditions: []metav1.Condition{{
+				Status:             metav1.ConditionTrue,
+				Type:               string(tsapi.ProxyClassReady),
+				ObservedGeneration: pc.Generation,
+			}},
+		}
+	})
+	expectReconciled(t, sr, "default", "test")
+	fullName, shortName := findGenName(t, fc, "default", "test", "svc")
+	opts := configOpts{
+		replicas:        new(int32(1)),
+		stsName:         shortName,
+		secretName:      fullName,
+		namespace:       "default",
+		parentType:      "svc",
+		hostname:        "default-test",
+		clusterTargetIP: "10.20.30.40",
+		app:             kubetypes.AppIngressProxy,
+		proxyClass:      pc.Name,
+	}
+	expectEqual(t, fc, expectedSecret(t, fc, opts))
+	expectEqual(t, fc, expectedHeadlessService(shortName, "svc"))
+	expectEqual(t, fc, expectedSTS(t, fc, opts), removeResourceReqs)
+}
+
+func TestProxyClassHandlerForSvc(t *testing.T) {
+	svc := func(name string, annotations, labels map[string]string) *corev1.Service {
+		return &corev1.Service{
+			ObjectMeta: metav1.ObjectMeta{
+				Name:        name,
+				Namespace:   "default",
+				Annotations: annotations,
+				Labels:      labels,
+			},
+			Spec: corev1.ServiceSpec{
+				ClusterIP: "1.2.3.4",
+			},
+		}
+	}
+	lbSvc := func(name string, annotations map[string]string, class *string) *corev1.Service {
+		return &corev1.Service{
+			ObjectMeta: metav1.ObjectMeta{
+				Name:        name,
+				Namespace:   "foo",
+				Annotations: annotations,
+			},
+			Spec: corev1.ServiceSpec{
+				Type:              corev1.ServiceTypeLoadBalancer,
+				LoadBalancerClass: class,
+				ClusterIP:         "1.2.3.4",
+			},
+		}
+	}
+
+	const (
+		defaultPCName      = "default-proxyclass"
+		otherPCName        = "other-proxyclass"
+		unreferencedPCName = "unreferenced-proxyclass"
+	)
+	fc := fake.NewClientBuilder().
+		WithScheme(tsapi.GlobalScheme).
+		WithIndex(&corev1.Service{}, indexServiceProxyClass, indexProxyClass).
+		WithIndex(&corev1.Service{}, indexServiceExposed, indexExposed).
+		WithIndex(&corev1.Service{}, indexServiceType, indexType).
+		WithObjects(
+			svc("not-exposed", nil, nil),
+			svc("exposed-default", map[string]string{AnnotationExpose: "true"}, nil),
+			svc("exposed-other", map[string]string{AnnotationExpose: "true", LabelAnnotationProxyClass: otherPCName}, nil),
+			svc("annotated", map[string]string{LabelAnnotationProxyClass: defaultPCName}, nil),
+			svc("labelled", nil, map[string]string{LabelAnnotationProxyClass: defaultPCName}),
+			lbSvc("lb-svc", nil, new("tailscale")),
+			lbSvc("lb-svc-no-class", nil, nil),
+			lbSvc("lb-svc-other-class", nil, new("other")),
+			lbSvc("lb-svc-other-pc", map[string]string{LabelAnnotationProxyClass: otherPCName}, nil),
+		).
+		Build()
+
+	zl := zap.Must(zap.NewDevelopment())
+	mapFunc := proxyClassHandlerForSvc(fc, zl.Sugar(), defaultPCName, true)
+
+	for _, tc := range []struct {
+		name           string
+		proxyClassName string
+		expected       []reconcile.Request
+	}{
+		{
+			name:           "default_ProxyClass",
+			proxyClassName: defaultPCName,
+			expected: []reconcile.Request{
+				{NamespacedName: types.NamespacedName{Namespace: "default", Name: "exposed-default"}},
+				{NamespacedName: types.NamespacedName{Namespace: "default", Name: "annotated"}},
+				{NamespacedName: types.NamespacedName{Namespace: "default", Name: "labelled"}},
+				{NamespacedName: types.NamespacedName{Namespace: "foo", Name: "lb-svc"}},
+				{NamespacedName: types.NamespacedName{Namespace: "foo", Name: "lb-svc-no-class"}},
+			},
+		},
+		{
+			name:           "other_ProxyClass",
+			proxyClassName: otherPCName,
+			expected: []reconcile.Request{
+				{NamespacedName: types.NamespacedName{Namespace: "default", Name: "exposed-other"}},
+				{NamespacedName: types.NamespacedName{Namespace: "foo", Name: "lb-svc-other-pc"}},
+			},
+		},
+		{
+			name:           "unreferenced_ProxyClass",
+			proxyClassName: unreferencedPCName,
+			expected:       nil,
+		},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			reqs := mapFunc(t.Context(), &tsapi.ProxyClass{
+				ObjectMeta: metav1.ObjectMeta{
+					Name: tc.proxyClassName,
+				},
+			})
+			if len(reqs) != len(tc.expected) {
+				t.Fatalf("expected %d requests, got %d: %v", len(tc.expected), len(reqs), reqs)
+			}
+			for _, expected := range tc.expected {
+				if !slices.Contains(reqs, expected) {
+					t.Errorf("expected request for Service %q not found in results: %v", expected.Name, reqs)
+				}
+			}
+		})
+	}
+}
diff --git a/cmd/k8s-operator/testutils_test.go b/cmd/k8s-operator/testutils_test.go
index d418f01284b95..36b608ef6f4fd 100644
--- a/cmd/k8s-operator/testutils_test.go
+++ b/cmd/k8s-operator/testutils_test.go
@@ -529,7 +529,7 @@ func expectedSecret(t *testing.T, cl client.Client, opts configOpts) *corev1.Sec
 		AcceptDNS:           "false",
 		Hostname:            &opts.hostname,
 		Locked:              "false",
-		AuthKey:             new("secret-authkey"),
+		AuthKey:             new("new-authkey"),
 		AcceptRoutes:        "false",
 		AppConnector:        &ipn.AppConnectorPrefs{Advertise: false},
 		NoStatefulFiltering: "true",
@@ -859,7 +859,7 @@ func (c *fakeTSClient) CreateKey(ctx context.Context, caps tailscale.KeyCapabili
 		Created:      time.Now(),
 		Capabilities: caps,
 	}
-	return "secret-authkey", k, nil
+	return "new-authkey", k, nil
 }
 
 func (c *fakeTSClient) Device(ctx context.Context, deviceID string, fields *tailscale.DeviceFieldsOpts) (*tailscale.Device, error) {
diff --git a/cmd/k8s-operator/tsrecorder_test.go b/cmd/k8s-operator/tsrecorder_test.go
index 0e1641243c937..d3ebc3bd5eaa8 100644
--- a/cmd/k8s-operator/tsrecorder_test.go
+++ b/cmd/k8s-operator/tsrecorder_test.go
@@ -284,7 +284,7 @@ func expectRecorderResources(t *testing.T, fc client.WithWatch, tsr *tsapi.Recor
 	}
 
 	for replica := range replicas {
-		auth := tsrAuthSecret(tsr, tsNamespace, "secret-authkey", replica)
+		auth := tsrAuthSecret(tsr, tsNamespace, "new-authkey", replica)
 		state := tsrStateSecret(tsr, tsNamespace, replica)
 
 		if shouldExist {
diff --git a/docs/architecture.md b/docs/architecture.md
new file mode 100644
index 0000000000000..1830ebb707b39
--- /dev/null
+++ b/docs/architecture.md
@@ -0,0 +1,68 @@
+# SCION Integration Architecture
+
+## Component Overview
+
+SCION is added as a third transport in `magicsock.Conn`, alongside the existing IPv4/IPv6 UDP and DERP relay transports. The `endpoint.betterAddr` mechanism selects the best path across all three.
+
+
+### Key Files (`wgengine/magicsock/`)
+
+| File | Role |
+|------|------|
+| `magicsock_scion.go` | Connection setup, path registry, send/receive, `ReconfigureSCION()` |
+| `magicsock_scion_conn.go` | SCION connection lifecycle (init, close, bind) |
+| `endpoint_scion.go` | Per-peer SCION state, heartbeat, path probing, pong handling |
+| `scion_bootstrap.go` | Topology/TRC fetch from bootstrap servers, DNS SRV discovery |
+| `scion_embedded.go` | In-process SCION daemon (no external sciond needed) |
+| `magicsock_scion_omit.go` | No-op stubs for `ts_omit_scion` builds |
+| `ipn/localapi/localapi_scion.go` | `GET /localapi/v0/scion-status` handler |
+| `ipn/ipnlocal/local.go` | SCION service advertisement + peerapi4 piggyback (lines 4892-4906) |
+
+## Connection Flow
+
+`trySCIONConnect()` uses a cascading fallback strategy:
+
+1. **External daemon** -- connects to sciond via gRPC at `SCION_DAEMON_ADDRESS` (default `127.0.0.1:30255`). Probes `Paths()` to detect version mismatch. *Skipped if `TS_SCION_EMBEDDED=1`.*
+
+2. **Embedded daemon with local topology** -- checks for topology file at:
+   - `TS_SCION_TOPOLOGY` (explicit path)
+   - `/etc/scion/topology.json` (Linux default)
+   - `<stateDir>/scion/topology.json` (from prior bootstrap)
+
+   Creates an in-process `embeddedConnector` with topology loader + segment fetcher (accept-all verification, Phase 1). *Skipped if `TS_SCION_FORCE_BOOTSTRAP=1`.*
+
+3. **Bootstrap + embedded** -- tries each URL from `bootstrapURLs()` in order:
+   1. Explicit `TS_SCION_BOOTSTRAP_URL`
+   2. Comma-separated `TS_SCION_BOOTSTRAP_URLS`
+   3. DNS SRV: `_sciondiscovery._tcp.<local-search-domain>`
+   4. Hardcoded defaults (ovgu.de, uva, ethz.ch)
+
+   For each URL: fetches `topology.json` + TRCs (TRCs optional) → saves to stateDir → creates embedded daemon with bootstrapped topology.
+
+**Android**: `ReconfigureSCION()` forces `TS_SCION_EMBEDDED=1` + `TS_SCION_FORCE_BOOTSTRAP=1`, always skipping steps 1-2 and going straight to bootstrap.
+
+## Data Flow
+
+**Outbound**: `endpoint.send()` → if bestAddr is SCION → `sendSCION()` → pre-serialized SCION header + WireGuard payload → UDP to first-hop border router.
+
+**Inbound**: `receiveSCION()` → parse SCION header (slayers) → extract source IA + host → route to endpoint via reverse index → deliver WireGuard payload.
+
+**Path discovery**: `refreshSCIONPaths()` runs every 30s → queries daemon `Paths()` → discovers up to 5 paths per peer (`TS_SCION_MAX_PROBE_PATHS`) → probes latency via disco pings → `betterAddr` promotes best path (with configurable SCION preference bonus).
+
+## Key Design Decisions
+
+- **Third transport, not replacement.** SCION runs alongside IPv4/IPv6 UDP. Fallback is automatic -- if SCION is unavailable, direct or relay paths are used.
+
+- **Path selection via `betterAddr`.** SCION paths get a configurable preference bonus (`TS_SCION_PREFERENCE`, default 15 points). +25 additional points when both peers have the `NodeAttrSCIONPrefer` capability. Incumbent bias prevents flapping (candidate must be >=20% or >=2ms faster).
+
+- **Embedded daemon.** `scion_embedded.go` implements `daemon.Connector` with an in-process topology loader and segment fetcher. No external sciond process required -- critical for Android.
+
+- **Bootstrap discovery.** `scion_bootstrap.go` discovers topology via DNS SRV (`_sciondiscovery._tcp`) or hardcoded fallback URLs. TRC fetch is best-effort (Phase 1: accept-all verification).
+
+- **Fast-path sends.** Pre-serialized SCION+UDP header templates (`scionFastPath`) avoid per-packet allocation. Batch send via `sendmmsg` where available. Disable with `TS_SCION_NO_FAST_PATH`.
+
+- **Build tag `ts_omit_scion`.** Compiles out all SCION code via no-op stubs. Feature flag `buildfeatures.HasSCION` set at compile time. Produces smaller binary with no scionproto dependency.
+
+- **Service advertisement via peerapi4 piggyback.** The Tailscale coordination server only relays `peerapi4`/`peerapi6` services to peers — it drops unknown service types. To work without coord server changes, SCION address info is piggybacked onto the `peerapi4` service's `Description` field as `scion=ISD-AS,[hostIP]:port` (see `ipn/ipnlocal/local.go:4892-4906`). Bracket notation around the IP ensures unambiguous parsing for both IPv4 and IPv6 underlay addresses. A standalone `tailcfg.ServiceProto("scion")` entry is also advertised for future coord server support. On the receiving side, `scionServiceFromPeer()` checks for a dedicated SCION service first, then falls back to parsing the peerapi4 piggyback (with backward compatibility for unbracketed format).
+
+- **Cross-platform.** Platform-specific DNS search domain resolution in `scion_bootstrap_unix.go` (Linux, macOS, BSDs), `scion_bootstrap_windows.go`, and `scion_bootstrap_other.go` (Android fallback).
\ No newline at end of file
diff --git a/feature/buildfeatures/feature_scion_disabled.go b/feature/buildfeatures/feature_scion_disabled.go
new file mode 100644
index 0000000000000..a6cbf2502e01d
--- /dev/null
+++ b/feature/buildfeatures/feature_scion_disabled.go
@@ -0,0 +1,13 @@
+// Copyright (c) Tailscale Inc & contributors
+// SPDX-License-Identifier: BSD-3-Clause
+
+// Code generated by gen.go; DO NOT EDIT.
+
+//go:build ts_omit_scion
+
+package buildfeatures
+
+// HasSCION is whether the binary was built with support for modular feature "SCION network integration".
+// Specifically, it's whether the binary was NOT built with the "ts_omit_scion" build tag.
+// It's a const so it can be used for dead code elimination.
+const HasSCION = false
diff --git a/feature/buildfeatures/feature_scion_enabled.go b/feature/buildfeatures/feature_scion_enabled.go
new file mode 100644
index 0000000000000..24be474ad49ca
--- /dev/null
+++ b/feature/buildfeatures/feature_scion_enabled.go
@@ -0,0 +1,13 @@
+// Copyright (c) Tailscale Inc & contributors
+// SPDX-License-Identifier: BSD-3-Clause
+
+// Code generated by gen.go; DO NOT EDIT.
+
+//go:build !ts_omit_scion
+
+package buildfeatures
+
+// HasSCION is whether the binary was built with support for modular feature "SCION network integration".
+// Specifically, it's whether the binary was NOT built with the "ts_omit_scion" build tag.
+// It's a const so it can be used for dead code elimination.
+const HasSCION = true
diff --git a/feature/conn25/conn25.go b/feature/conn25/conn25.go
index b5d0dc9dfe155..5318d2bdde3ed 100644
--- a/feature/conn25/conn25.go
+++ b/feature/conn25/conn25.go
@@ -26,6 +26,7 @@ import (
 	"tailscale.com/ipn/ipnext"
 	"tailscale.com/ipn/ipnlocal"
 	"tailscale.com/net/dns"
+	"tailscale.com/net/tsaddr"
 	"tailscale.com/tailcfg"
 	"tailscale.com/types/appctype"
 	"tailscale.com/types/logger"
@@ -131,7 +132,7 @@ func (e *extension) handleConnectorTransitIP(h ipnlocal.PeerAPIHandler, w http.R
 		http.Error(w, "Error decoding JSON", http.StatusBadRequest)
 		return
 	}
-	resp := e.conn25.handleConnectorTransitIPRequest(h.Peer().ID(), req)
+	resp := e.conn25.handleConnectorTransitIPRequest(h.Peer(), req)
 	bs, err := json.Marshal(resp)
 	if err != nil {
 		http.Error(w, "Error encoding JSON", http.StatusInternalServerError)
@@ -248,47 +249,94 @@ func (c *Conn25) mapDNSResponse(buf []byte) []byte {
 }
 
 const dupeTransitIPMessage = "Duplicate transit address in ConnectorTransitIPRequest"
+const noMatchingPeerIPFamilyMessage = "No peer IP found with matching IP family"
+const addrFamilyMismatchMessage = "Transit and Destination addresses must have matching IP family"
+const unknownAppNameMessage = "The App name in the request does not match a configured App"
+
+// handleConnectorTransitIPRequest creates a ConnectorTransitIPResponse in response
+// to a ConnectorTransitIPRequest. It updates the connectors mapping of
+// TransitIP->DestinationIP per peer (using the Peer's IP that matches the address
+// family of the transitIP). If a peer has stored this mapping in the connector,
+// Conn25 will route traffic to TransitIPs to DestinationIPs for that peer.
+func (c *Conn25) handleConnectorTransitIPRequest(n tailcfg.NodeView, ctipr ConnectorTransitIPRequest) ConnectorTransitIPResponse {
+	var peerIPv4, peerIPv6 netip.Addr
+	for _, ip := range n.Addresses().All() {
+		if !ip.IsSingleIP() || !tsaddr.IsTailscaleIP(ip.Addr()) {
+			continue
+		}
+		if ip.Addr().Is4() && !peerIPv4.IsValid() {
+			peerIPv4 = ip.Addr()
+		} else if ip.Addr().Is6() && !peerIPv6.IsValid() {
+			peerIPv6 = ip.Addr()
+		}
+	}
 
-// handleConnectorTransitIPRequest creates a ConnectorTransitIPResponse in response to a ConnectorTransitIPRequest.
-// It updates the connectors mapping of TransitIP->DestinationIP per peer (tailcfg.NodeID).
-// If a peer has stored this mapping in the connector Conn25 will route traffic to TransitIPs to DestinationIPs for that peer.
-func (c *Conn25) handleConnectorTransitIPRequest(nid tailcfg.NodeID, ctipr ConnectorTransitIPRequest) ConnectorTransitIPResponse {
 	resp := ConnectorTransitIPResponse{}
 	seen := map[netip.Addr]bool{}
 	for _, each := range ctipr.TransitIPs {
 		if seen[each.TransitIP] {
 			resp.TransitIPs = append(resp.TransitIPs, TransitIPResponse{
-				Code:    OtherFailure,
+				Code:    DuplicateTransitIP,
 				Message: dupeTransitIPMessage,
 			})
+			c.connector.logf("[Unexpected] peer attempt to map a transit IP reused a transitIP: node: %s, IP: %v",
+				n.StableID(), each.TransitIP)
 			continue
 		}
-		tipresp := c.connector.handleTransitIPRequest(nid, each)
+		tipresp := c.connector.handleTransitIPRequest(n, peerIPv4, peerIPv6, each)
 		seen[each.TransitIP] = true
 		resp.TransitIPs = append(resp.TransitIPs, tipresp)
 	}
 	return resp
 }
 
-func (s *connector) handleTransitIPRequest(nid tailcfg.NodeID, tipr TransitIPRequest) TransitIPResponse {
+func (s *connector) handleTransitIPRequest(n tailcfg.NodeView, peerV4 netip.Addr, peerV6 netip.Addr, tipr TransitIPRequest) TransitIPResponse {
+	if tipr.TransitIP.Is4() != tipr.DestinationIP.Is4() {
+		s.logf("[Unexpected] peer attempt to map a transit IP to dest IP did not have matching families: node: %s, tIPv4: %v dIPv4: %v",
+			n.StableID(), tipr.TransitIP.Is4(), tipr.DestinationIP.Is4())
+		return TransitIPResponse{Code: AddrFamilyMismatch, Message: addrFamilyMismatchMessage}
+	}
+
+	// Datapath lookups only have access to the peer IP, and that will match the family
+	// of the transit IP, so we need to store v4 and v6 mappings separately.
+	var peerAddr netip.Addr
+	if tipr.TransitIP.Is4() {
+		peerAddr = peerV4
+	} else {
+		peerAddr = peerV6
+	}
+
+	// If we couldn't find a matching family, return an error.
+	if !peerAddr.IsValid() {
+		s.logf("[Unexpected] peer attempt to map a transit IP did not have a matching address family: node: %s, IPv4: %v",
+			n.StableID(), tipr.TransitIP.Is4())
+		return TransitIPResponse{NoMatchingPeerIPFamily, noMatchingPeerIPFamilyMessage}
+	}
+
 	s.mu.Lock()
 	defer s.mu.Unlock()
+	if _, ok := s.config.appsByName[tipr.App]; !ok {
+		s.logf("[Unexpected] peer attempt to map a transit IP referenced unknown app: node: %s, app: %q",
+			n.StableID(), tipr.App)
+		return TransitIPResponse{Code: UnknownAppName, Message: unknownAppNameMessage}
+	}
+
 	if s.transitIPs == nil {
-		s.transitIPs = make(map[tailcfg.NodeID]map[netip.Addr]appAddr)
+		s.transitIPs = make(map[netip.Addr]map[netip.Addr]appAddr)
 	}
-	peerMap, ok := s.transitIPs[nid]
+	peerMap, ok := s.transitIPs[peerAddr]
 	if !ok {
 		peerMap = make(map[netip.Addr]appAddr)
-		s.transitIPs[nid] = peerMap
+		s.transitIPs[peerAddr] = peerMap
 	}
 	peerMap[tipr.TransitIP] = appAddr{addr: tipr.DestinationIP, app: tipr.App}
 	return TransitIPResponse{}
 }
 
-func (s *connector) transitIPTarget(nid tailcfg.NodeID, tip netip.Addr) netip.Addr {
+func (s *connector) transitIPTarget(peerIP, tip netip.Addr) netip.Addr {
 	s.mu.Lock()
 	defer s.mu.Unlock()
-	return s.transitIPs[nid][tip].addr
+	return s.transitIPs[peerIP][tip].addr
 }
 
 // TransitIPRequest details a single TransitIP allocation request from a client to a
@@ -322,8 +370,24 @@ const (
 	OK TransitIPResponseCode = 0
 
 	// OtherFailure indicates that the mapping failed for a reason that does not have
-	// another relevant [TransitIPResponsecode].
+	// another relevant [TransitIPResponseCode].
 	OtherFailure TransitIPResponseCode = 1
+
+	// DuplicateTransitIP indicates that the same transit address appeared more than
+	// once in a [ConnectorTransitIPRequest].
+	DuplicateTransitIP TransitIPResponseCode = 2
+
+	// NoMatchingPeerIPFamily indicates that the peer did not have an associated
+	// IP with the same family as transit IP being registered.
+	NoMatchingPeerIPFamily = 3
+
+	// AddrFamilyMismatch indicates that the transit IP and destination IP addresses
+	// do not belong to the same IP family.
+	AddrFamilyMismatch = 4
+
+	// UnknownAppName indicates that the connector is not configured to handle requests
+	// for the App name that was specified in the request.
+	UnknownAppName = 5
 )
 
 // TransitIPResponse is the response to a TransitIPRequest
@@ -651,8 +715,9 @@ type connector struct {
 	logf logger.Logf
 
 	mu sync.Mutex // protects the fields below
-	// transitIPs is a map of connector client peer NodeID -> client transitIPs that we update as connector client peers instruct us to, and then use to route traffic to its destination on behalf of connector clients.
-	transitIPs map[tailcfg.NodeID]map[netip.Addr]appAddr
+	// transitIPs is a map of connector client peer IP -> client transitIPs that we update as connector client peers instruct us to, and then use to route traffic to its destination on behalf of connector clients.
+	// Note that each peer could potentially have two maps: one for its IPv4 address, and one for its IPv6 address. The transit IPs map for a given peer IP will contain transit IPs of the same family as the peer's IP.
+	transitIPs map[netip.Addr]map[netip.Addr]appAddr
 	config     config
 }
 
diff --git a/feature/conn25/conn25_test.go b/feature/conn25/conn25_test.go
index 97a22c50017df..574320af8db78 100644
--- a/feature/conn25/conn25_test.go
+++ b/feature/conn25/conn25_test.go
@@ -38,180 +38,347 @@ func mustIPSetFromPrefix(s string) *netipx.IPSet {
 	return set
 }
 
-// TestHandleConnectorTransitIPRequestZeroLength tests that if sent a
-// ConnectorTransitIPRequest with 0 TransitIPRequests, we respond with a
-// ConnectorTransitIPResponse with 0 TransitIPResponses.
-func TestHandleConnectorTransitIPRequestZeroLength(t *testing.T) {
-	c := newConn25(logger.Discard)
-	req := ConnectorTransitIPRequest{}
-	nid := tailcfg.NodeID(1)
+// TestHandleConnectorTransitIPRequest tests that if sent a
+// request with a transit addr and a destination addr we store that mapping
+// and can retrieve it.
+func TestHandleConnectorTransitIPRequest(t *testing.T) {
 
-	resp := c.handleConnectorTransitIPRequest(nid, req)
-	if len(resp.TransitIPs) != 0 {
-		t.Fatalf("n TransitIPs in response: %d, want 0", len(resp.TransitIPs))
-	}
-}
+	const appName = "TestApp"
 
-// TestHandleConnectorTransitIPRequestStoresAddr tests that if sent a
-// request with a transit addr and a destination addr we store that mapping
-// and can retrieve it. If sent another req with a different dst for that transit addr
-// we store that instead.
-func TestHandleConnectorTransitIPRequestStoresAddr(t *testing.T) {
-	c := newConn25(logger.Discard)
-	nid := tailcfg.NodeID(1)
-	tip := netip.MustParseAddr("0.0.0.1")
-	dip := netip.MustParseAddr("1.2.3.4")
-	dip2 := netip.MustParseAddr("1.2.3.5")
-	mr := func(t, d netip.Addr) ConnectorTransitIPRequest {
-		return ConnectorTransitIPRequest{
-			TransitIPs: []TransitIPRequest{
-				{TransitIP: t, DestinationIP: d},
-			},
-		}
-	}
+	// Peer IPs
+	pipV4_1 := netip.MustParseAddr("100.101.101.101")
+	pipV4_2 := netip.MustParseAddr("100.101.101.102")
 
-	resp := c.handleConnectorTransitIPRequest(nid, mr(tip, dip))
-	if len(resp.TransitIPs) != 1 {
-		t.Fatalf("n TransitIPs in response: %d, want 1", len(resp.TransitIPs))
-	}
-	got := resp.TransitIPs[0].Code
-	if got != TransitIPResponseCode(0) {
-		t.Fatalf("TransitIP Code: %d, want 0", got)
-	}
-	gotAddr := c.connector.transitIPTarget(nid, tip)
-	if gotAddr != dip {
-		t.Fatalf("Connector stored destination for tip: %v, want %v", gotAddr, dip)
-	}
+	pipV6_1 := netip.MustParseAddr("fd7a:115c:a1e0::101")
+	pipV6_3 := netip.MustParseAddr("fd7a:115c:a1e0::103")
 
-	// mapping can be overwritten
-	resp2 := c.handleConnectorTransitIPRequest(nid, mr(tip, dip2))
-	if len(resp2.TransitIPs) != 1 {
-		t.Fatalf("n TransitIPs in response: %d, want 1", len(resp2.TransitIPs))
-	}
-	got2 := resp.TransitIPs[0].Code
-	if got2 != TransitIPResponseCode(0) {
-		t.Fatalf("TransitIP Code: %d, want 0", got2)
-	}
-	gotAddr2 := c.connector.transitIPTarget(nid, tip)
-	if gotAddr2 != dip2 {
-		t.Fatalf("Connector stored destination for tip: %v, want %v", gotAddr, dip2)
-	}
-}
+	// Transit IPs
+	tipV4_1 := netip.MustParseAddr("0.0.0.1")
+	tipV4_2 := netip.MustParseAddr("0.0.0.2")
 
-// TestHandleConnectorTransitIPRequestMultipleTIP tests that we can
-// get a req with multiple mappings and we store them all. Including
-// multiple transit addrs for the same destination.
-func TestHandleConnectorTransitIPRequestMultipleTIP(t *testing.T) {
-	c := newConn25(logger.Discard)
-	nid := tailcfg.NodeID(1)
-	tip := netip.MustParseAddr("0.0.0.1")
-	tip2 := netip.MustParseAddr("0.0.0.2")
-	tip3 := netip.MustParseAddr("0.0.0.3")
-	dip := netip.MustParseAddr("1.2.3.4")
-	dip2 := netip.MustParseAddr("1.2.3.5")
-	req := ConnectorTransitIPRequest{
-		TransitIPs: []TransitIPRequest{
-			{TransitIP: tip, DestinationIP: dip},
-			{TransitIP: tip2, DestinationIP: dip2},
-			// can store same dst addr for multiple transit addrs
-			{TransitIP: tip3, DestinationIP: dip},
-		},
-	}
-	resp := c.handleConnectorTransitIPRequest(nid, req)
-	if len(resp.TransitIPs) != 3 {
-		t.Fatalf("n TransitIPs in response: %d, want 3", len(resp.TransitIPs))
-	}
+	tipV6_1 := netip.MustParseAddr("FE80::1")
 
-	for i := range 3 {
-		got := resp.TransitIPs[i].Code
-		if got != TransitIPResponseCode(0) {
-			t.Fatalf("i=%d TransitIP Code: %d, want 0", i, got)
-		}
-	}
-	gotAddr1 := c.connector.transitIPTarget(nid, tip)
-	if gotAddr1 != dip {
-		t.Fatalf("Connector stored destination for tip(%v): %v, want %v", tip, gotAddr1, dip)
-	}
-	gotAddr2 := c.connector.transitIPTarget(nid, tip2)
-	if gotAddr2 != dip2 {
-		t.Fatalf("Connector stored destination for tip(%v): %v, want %v", tip2, gotAddr2, dip2)
-	}
-	gotAddr3 := c.connector.transitIPTarget(nid, tip3)
-	if gotAddr3 != dip {
-		t.Fatalf("Connector stored destination for tip(%v): %v, want %v", tip3, gotAddr3, dip)
-	}
-}
+	// Destination IPs
+	dipV4_1 := netip.MustParseAddr("10.0.0.1")
+	dipV4_2 := netip.MustParseAddr("10.0.0.2")
+	dipV4_3 := netip.MustParseAddr("10.0.0.3")
 
-// TestHandleConnectorTransitIPRequestSameTIP tests that if we get
-// a req that has more than one TransitIPRequest for the same transit addr
-// only the first is stored, and the subsequent ones get an error code and
-// message in the response.
-func TestHandleConnectorTransitIPRequestSameTIP(t *testing.T) {
-	c := newConn25(logger.Discard)
-	nid := tailcfg.NodeID(1)
-	tip := netip.MustParseAddr("0.0.0.1")
-	tip2 := netip.MustParseAddr("0.0.0.2")
-	dip := netip.MustParseAddr("1.2.3.4")
-	dip2 := netip.MustParseAddr("1.2.3.5")
-	dip3 := netip.MustParseAddr("1.2.3.6")
-	req := ConnectorTransitIPRequest{
-		TransitIPs: []TransitIPRequest{
-			{TransitIP: tip, DestinationIP: dip},
-			// cannot have dupe TransitIPs in one ConnectorTransitIPRequest
-			{TransitIP: tip, DestinationIP: dip2},
-			{TransitIP: tip2, DestinationIP: dip3},
+	dipV6_1 := netip.MustParseAddr("fc00::1")
+
+	// Peer nodes
+	peerV4V6 := (&tailcfg.Node{
+		ID:        tailcfg.NodeID(1),
+		Addresses: []netip.Prefix{netip.PrefixFrom(pipV4_1, 32), netip.PrefixFrom(pipV6_1, 128)},
+	}).View()
+
+	peerV4Only := (&tailcfg.Node{
+		ID:        tailcfg.NodeID(2),
+		Addresses: []netip.Prefix{netip.PrefixFrom(pipV4_2, 32)},
+	}).View()
+
+	peerV6Only := (&tailcfg.Node{
+		ID:        tailcfg.NodeID(3),
+		Addresses: []netip.Prefix{netip.PrefixFrom(pipV6_3, 128)},
+	}).View()
+
+	tests := []struct {
+		name         string
+		ctipReqPeers []tailcfg.NodeView           // One entry per request and the other
+		ctipReqs     []ConnectorTransitIPRequest  // arrays in this struct must have the same
+		wants        []ConnectorTransitIPResponse // cardinality
+		// For checking lookups:
+		//	The outer array needs to correspond to the number of requests,
+		//	can be nil if no lookups need to be done after the request is processed.
+		//
+		//	The middle array is the set of lookups for the corresponding request.
+		//
+		//	The inner array is a tuple of (PeerIP, TransitIP, ExpectedDestinationIP)
+		wantLookups [][][]netip.Addr
+	}{
+		// Single peer, single request with success ipV4
+		{
+			name:         "one-peer-one-req-ipv4",
+			ctipReqPeers: []tailcfg.NodeView{peerV4Only},
+			ctipReqs: []ConnectorTransitIPRequest{
+				{TransitIPs: []TransitIPRequest{{TransitIP: tipV4_1, DestinationIP: dipV4_1, App: appName}}},
+			},
+			wants: []ConnectorTransitIPResponse{
+				{TransitIPs: []TransitIPResponse{{Code: OK, Message: ""}}},
+			},
+			wantLookups: [][][]netip.Addr{
+				{{pipV4_2, tipV4_1, dipV4_1}},
+			},
+		},
+		// Single peer, single request with success ipV6
+		{
+			name:         "one-peer-one-req-ipv6",
+			ctipReqPeers: []tailcfg.NodeView{peerV6Only},
+			ctipReqs: []ConnectorTransitIPRequest{
+				{TransitIPs: []TransitIPRequest{{TransitIP: tipV6_1, DestinationIP: dipV6_1, App: appName}}},
+			},
+			wants: []ConnectorTransitIPResponse{
+				{TransitIPs: []TransitIPResponse{{Code: OK, Message: ""}}},
+			},
+			wantLookups: [][][]netip.Addr{
+				{{pipV6_3, tipV6_1, dipV6_1}},
+			},
+		},
+		// Single peer, multi request with success, ipV4
+		{
+			name:         "one-peer-multi-req-ipv4",
+			ctipReqPeers: []tailcfg.NodeView{peerV4Only, peerV4Only},
+			ctipReqs: []ConnectorTransitIPRequest{
+				{TransitIPs: []TransitIPRequest{{TransitIP: tipV4_1, DestinationIP: dipV4_1, App: appName}}},
+				{TransitIPs: []TransitIPRequest{{TransitIP: tipV4_2, DestinationIP: dipV4_2, App: appName}}},
+			},
+			wants: []ConnectorTransitIPResponse{
+				{TransitIPs: []TransitIPResponse{{Code: OK, Message: ""}}},
+				{TransitIPs: []TransitIPResponse{{Code: OK, Message: ""}}},
+			},
+			wantLookups: [][][]netip.Addr{
+				{{pipV4_2, tipV4_1, dipV4_1}},
+				{{pipV4_2, tipV4_2, dipV4_2}},
+			},
+		},
+		// Single peer, multi request remap tip, ipV4
+		{
+			name:         "one-peer-remap-tip",
+			ctipReqPeers: []tailcfg.NodeView{peerV4Only, peerV4Only},
+			ctipReqs: []ConnectorTransitIPRequest{
+				{TransitIPs: []TransitIPRequest{{TransitIP: tipV4_1, DestinationIP: dipV4_1, App: appName}}},
+				{TransitIPs: []TransitIPRequest{{TransitIP: tipV4_1, DestinationIP: dipV4_2, App: appName}}},
+			},
+			wants: []ConnectorTransitIPResponse{
+				{TransitIPs: []TransitIPResponse{{Code: OK, Message: ""}}},
+				{TransitIPs: []TransitIPResponse{{Code: OK, Message: ""}}},
+			},
+			wantLookups: [][][]netip.Addr{
+				{{pipV4_2, tipV4_1, dipV4_1}},
+				{{pipV4_2, tipV4_1, dipV4_2}},
+			},
+		},
+		// Single peer, multi request with success, ipV4 and ipV6
+		{
+			name:         "one-peer-multi-req-ipv4-ipv6",
+			ctipReqPeers: []tailcfg.NodeView{peerV4V6, peerV4V6},
+			ctipReqs: []ConnectorTransitIPRequest{
+				{TransitIPs: []TransitIPRequest{{TransitIP: tipV4_1, DestinationIP: dipV4_1, App: appName}}},
+				{TransitIPs: []TransitIPRequest{{TransitIP: tipV6_1, DestinationIP: dipV6_1, App: appName}}},
+			},
+			wants: []ConnectorTransitIPResponse{
+				{TransitIPs: []TransitIPResponse{{Code: OK, Message: ""}}},
+				{TransitIPs: []TransitIPResponse{{Code: OK, Message: ""}}},
+			},
+			wantLookups: [][][]netip.Addr{
+				{{pipV4_1, tipV4_1, dipV4_1}},
+				{{pipV4_1, tipV4_1, dipV4_1}, {pipV6_1, tipV6_1, dipV6_1}, {pipV4_1, tipV6_1, netip.Addr{}}},
+			},
+		},
+		// Single peer, multi map with success, ipV4
+		{
+			name:         "one-peer-multi-map-ipv4",
+			ctipReqPeers: []tailcfg.NodeView{peerV4Only},
+			ctipReqs: []ConnectorTransitIPRequest{
+				{TransitIPs: []TransitIPRequest{
+					{TransitIP: tipV4_1, DestinationIP: dipV4_1, App: appName},
+					{TransitIP: tipV4_2, DestinationIP: dipV4_2, App: appName},
+				}},
+			},
+			wants: []ConnectorTransitIPResponse{
+				{TransitIPs: []TransitIPResponse{{Code: OK, Message: ""}, {Code: OK, Message: ""}}},
+			},
+			wantLookups: [][][]netip.Addr{
+				{{pipV4_2, tipV4_1, dipV4_1}, {pipV4_2, tipV4_2, dipV4_2}},
+			},
+		},
+		// Single peer, error reuse same tip in one request, ensure all non-dup requests are processed
+		{
+			name:         "one-peer-multi-map-duplicate-tip",
+			ctipReqPeers: []tailcfg.NodeView{peerV4Only},
+			ctipReqs: []ConnectorTransitIPRequest{
+				{TransitIPs: []TransitIPRequest{
+					{TransitIP: tipV4_1, DestinationIP: dipV4_1, App: appName},
+					{TransitIP: tipV4_1, DestinationIP: dipV4_2, App: appName},
+					{TransitIP: tipV4_2, DestinationIP: dipV4_3, App: appName},
+				}},
+			},
+			wants: []ConnectorTransitIPResponse{
+				{TransitIPs: []TransitIPResponse{
+					{Code: OK, Message: ""},
+					{Code: DuplicateTransitIP, Message: dupeTransitIPMessage},
+					{Code: OK, Message: ""}},
+				},
+			},
+			wantLookups: [][][]netip.Addr{
+				{{pipV4_2, tipV4_1, dipV4_1}, {pipV4_2, tipV4_2, dipV4_3}},
+			},
+		},
+		// Multi peer, success reuse same tip in one request
+		{
+			name:         "multi-peer-duplicate-tip",
+			ctipReqPeers: []tailcfg.NodeView{peerV4V6, peerV4Only},
+			ctipReqs: []ConnectorTransitIPRequest{
+				{TransitIPs: []TransitIPRequest{{TransitIP: tipV4_1, DestinationIP: dipV4_1, App: appName}}},
+				{TransitIPs: []TransitIPRequest{{TransitIP: tipV4_1, DestinationIP: dipV4_2, App: appName}}},
+			},
+			wants: []ConnectorTransitIPResponse{
+				{TransitIPs: []TransitIPResponse{{Code: OK, Message: ""}}},
+				{TransitIPs: []TransitIPResponse{{Code: OK, Message: ""}}},
+			},
+			wantLookups: [][][]netip.Addr{
+				{{pipV4_1, tipV4_1, dipV4_1}},
+				{{pipV4_1, tipV4_1, dipV4_1}, {pipV4_2, tipV4_1, dipV4_2}},
+			},
+		},
+		// Single peer, multi map, multiple tip to same dip
+		{
+			name:         "one-peer-multi-map-multi-tip-to-dip",
+			ctipReqPeers: []tailcfg.NodeView{peerV4Only},
+			ctipReqs: []ConnectorTransitIPRequest{
+				{TransitIPs: []TransitIPRequest{
+					{TransitIP: tipV4_1, DestinationIP: dipV4_1, App: appName},
+					{TransitIP: tipV4_2, DestinationIP: dipV4_1, App: appName},
+				}},
+			},
+			wants: []ConnectorTransitIPResponse{
+				{TransitIPs: []TransitIPResponse{{Code: OK, Message: ""}, {Code: OK, Message: ""}}},
+			},
+			wantLookups: [][][]netip.Addr{
+				{{pipV4_2, tipV4_1, dipV4_1}, {pipV4_2, tipV4_2, dipV4_1}},
+			},
+		},
+		// Single peer, ipv4 tip, no ipv4 pip, but ipv6 tip works
+		{
+			name:         "one-peer-missing-ipv4-family",
+			ctipReqPeers: []tailcfg.NodeView{peerV6Only},
+			ctipReqs: []ConnectorTransitIPRequest{
+				{TransitIPs: []TransitIPRequest{
+					{TransitIP: tipV4_1, DestinationIP: dipV4_1, App: appName},
+					{TransitIP: tipV6_1, DestinationIP: dipV6_1, App: appName},
+				}},
+			},
+			wants: []ConnectorTransitIPResponse{
+				{TransitIPs: []TransitIPResponse{
+					{Code: NoMatchingPeerIPFamily, Message: noMatchingPeerIPFamilyMessage},
+					{Code: OK, Message: ""},
+				}},
+			},
+			wantLookups: [][][]netip.Addr{
+				{{pipV6_3, tipV4_1, netip.Addr{}}, {pipV6_3, tipV6_1, dipV6_1}},
+			},
+		},
+		// Single peer, ipv6 tip, no ipv6 pip, but ipv4 tip works
+		{
+			name:         "one-peer-missing-ipv6-family",
+			ctipReqPeers: []tailcfg.NodeView{peerV4Only},
+			ctipReqs: []ConnectorTransitIPRequest{
+				{TransitIPs: []TransitIPRequest{
+					{TransitIP: tipV6_1, DestinationIP: dipV6_1, App: appName},
+					{TransitIP: tipV4_1, DestinationIP: dipV4_1, App: appName},
+				}},
+			},
+			wants: []ConnectorTransitIPResponse{
+				{TransitIPs: []TransitIPResponse{
+					{Code: NoMatchingPeerIPFamily, Message: noMatchingPeerIPFamilyMessage},
+					{Code: OK, Message: ""},
+				}},
+			},
+			wantLookups: [][][]netip.Addr{
+				{{pipV4_2, tipV6_1, netip.Addr{}}, {pipV4_2, tipV4_1, dipV4_1}},
+			},
+		},
+		// Single peer, mismatched transit and destination ips
+		{
+			name:         "one-peer-mismatched-tip-dip",
+			ctipReqPeers: []tailcfg.NodeView{peerV4Only},
+			ctipReqs: []ConnectorTransitIPRequest{
+				{TransitIPs: []TransitIPRequest{{TransitIP: tipV4_1, DestinationIP: dipV6_1, App: appName}}},
+			},
+			wants: []ConnectorTransitIPResponse{
+				{TransitIPs: []TransitIPResponse{{Code: AddrFamilyMismatch, Message: addrFamilyMismatchMessage}}},
+			},
+			wantLookups: [][][]netip.Addr{
+				{{pipV4_2, tipV4_1, netip.Addr{}}},
+			},
+		},
+		// Single peer, invalid app name
+		{
+			name:         "one-peer-invalid-app",
+			ctipReqPeers: []tailcfg.NodeView{peerV4Only},
+			ctipReqs: []ConnectorTransitIPRequest{
+				{TransitIPs: []TransitIPRequest{{TransitIP: tipV4_1, DestinationIP: dipV4_1, App: "Unknown App"}}},
+			},
+			wants: []ConnectorTransitIPResponse{
+				{TransitIPs: []TransitIPResponse{{Code: UnknownAppName, Message: unknownAppNameMessage}}},
+			},
+			wantLookups: [][][]netip.Addr{
+				{{pipV4_2, tipV4_1, netip.Addr{}}},
+			},
 		},
 	}
 
-	resp := c.handleConnectorTransitIPRequest(nid, req)
-	if len(resp.TransitIPs) != 3 {
-		t.Fatalf("n TransitIPs in response: %d, want 3", len(resp.TransitIPs))
-	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			switch {
+			case len(tt.ctipReqPeers) != len(tt.ctipReqs):
+				t.Fatalf("error in test setup: ctipReqPeers has length %d does not match ctipReqs length %d",
+					len(tt.ctipReqPeers), len(tt.ctipReqs))
+			case len(tt.ctipReqPeers) != len(tt.wants):
+				t.Fatalf("error in test setup: ctipReqPeers has length %d does not match wants length %d",
+					len(tt.ctipReqPeers), len(tt.wants))
+			case len(tt.ctipReqPeers) != len(tt.wantLookups):
+				t.Fatalf("error in test setup: ctipReqPeers has length %d does not match wantLookups length %d",
+					len(tt.ctipReqPeers), len(tt.wantLookups))
+			}
 
-	got := resp.TransitIPs[0].Code
-	if got != TransitIPResponseCode(0) {
-		t.Fatalf("i=0 TransitIP Code: %d, want 0", got)
-	}
-	msg := resp.TransitIPs[0].Message
-	if msg != "" {
-		t.Fatalf("i=0 TransitIP Message: \"%s\", want \"%s\"", msg, "")
-	}
-	got1 := resp.TransitIPs[1].Code
-	if got1 != TransitIPResponseCode(1) {
-		t.Fatalf("i=1 TransitIP Code: %d, want 1", got1)
-	}
-	msg1 := resp.TransitIPs[1].Message
-	if msg1 != dupeTransitIPMessage {
-		t.Fatalf("i=1 TransitIP Message: \"%s\", want \"%s\"", msg1, dupeTransitIPMessage)
-	}
-	got2 := resp.TransitIPs[2].Code
-	if got2 != TransitIPResponseCode(0) {
-		t.Fatalf("i=2 TransitIP Code: %d, want 0", got2)
-	}
-	msg2 := resp.TransitIPs[2].Message
-	if msg2 != "" {
-		t.Fatalf("i=2 TransitIP Message: \"%s\", want \"%s\"", msg, "")
-	}
+			// Use the same Conn25 for each request in the test and seed it with a test app name.
+			c := newConn25(logger.Discard)
+			c.connector.config = config{
+				appsByName: map[string]appctype.Conn25Attr{appName: {}},
+			}
 
-	gotAddr1 := c.connector.transitIPTarget(nid, tip)
-	if gotAddr1 != dip {
-		t.Fatalf("Connector stored destination for tip(%v): %v, want %v", tip, gotAddr1, dip)
-	}
-	gotAddr2 := c.connector.transitIPTarget(nid, tip2)
-	if gotAddr2 != dip3 {
-		t.Fatalf("Connector stored destination for tip(%v): %v, want %v", tip2, gotAddr2, dip3)
-	}
-}
+			for i, peer := range tt.ctipReqPeers {
+				req := tt.ctipReqs[i]
+				want := tt.wants[i]
 
-// TestGetDstIPUnknownTIP tests that unknown transit addresses can be looked up without problem.
-func TestTransitIPTargetUnknownTIP(t *testing.T) {
-	c := newConn25(logger.Discard)
-	nid := tailcfg.NodeID(1)
-	tip := netip.MustParseAddr("0.0.0.1")
-	got := c.connector.transitIPTarget(nid, tip)
-	want := netip.Addr{}
-	if got != want {
-		t.Fatalf("Unknown transit addr, want: %v, got %v", want, got)
+				resp := c.handleConnectorTransitIPRequest(peer, req)
+
+				// Ensure that we have the expected number of responses
+				if len(resp.TransitIPs) != len(want.TransitIPs) {
+					t.Fatalf("wrong number of TransitIPs in response %d: got %d, want %d",
+						i, len(resp.TransitIPs), len(want.TransitIPs))
+				}
+
+				// Validate the contents of each response
+				for j, tipResp := range resp.TransitIPs {
+					wantResp := want.TransitIPs[j]
+					if tipResp.Code != wantResp.Code {
+						t.Errorf("transitIP.Code mismatch in response %d, tipresp %d: got %d, want %d",
+							i, j, tipResp.Code, wantResp.Code)
+					}
+					if tipResp.Message != wantResp.Message {
+						t.Errorf("transitIP.Message mismatch in response %d, tipresp %d: got %q, want %q",
+							i, j, tipResp.Message, wantResp.Message)
+					}
+				}
+
+				// Validate the state of the transitIP map after each request
+				if tt.wantLookups[i] != nil {
+					for j, wantLookup := range tt.wantLookups[i] {
+						if len(wantLookup) != 3 {
+							t.Fatalf("test setup error: wantLookup for request %d lookup %d contains %d IPs, expected 3",
+								i, j, len(wantLookup))
+						}
+						pip, tip, wantDip := wantLookup[0], wantLookup[1], wantLookup[2]
+						gotDip := c.connector.transitIPTarget(pip, tip)
+						if gotDip != wantDip {
+							t.Errorf("wrong result on lookup[%d][%d] ([%v], [%v]): got [%v] expected [%v]",
+								i, j, pip, tip, gotDip, wantDip)
+						}
+					}
+				}
+			}
+		})
 	}
 }
 
diff --git a/feature/featuretags/featuretags.go b/feature/featuretags/featuretags.go
index 4220c02b75fa2..a3b916b0a5724 100644
--- a/feature/featuretags/featuretags.go
+++ b/feature/featuretags/featuretags.go
@@ -235,6 +235,7 @@ var Features = map[FeatureTag]FeatureMeta{
 		Desc: "Linux systemd-resolved integration",
 		Deps: []FeatureTag{"dbus"},
 	},
+	"scion": {Sym: "SCION", Desc: "SCION network integration"},
 	"sdnotify": {
 		Sym:  "SDNotify",
 		Desc: "systemd notification support",
diff --git a/flake.nix b/flake.nix
index 5ac0726dab25c..e32cf3866a28e 100644
--- a/flake.nix
+++ b/flake.nix
@@ -87,7 +87,7 @@
     # you're an end user you should be prepared for this flake to not
     # build periodically.
     packages = eachSystem (pkgs: rec {
-      default = pkgs.buildGo125Module {
+      default = pkgs.buildGo126Module {
         name = "tailscale";
         pname = "tailscale";
         src = ./.;
@@ -151,4 +151,4 @@
     });
   };
 }
-# nix-direnv cache busting line: sha256-dx+SJyDx+eZptFaMatoyM6w1E3nJKY+hKs7nuR997bE=
+# nix-direnv cache busting line: sha256-V4vJ1MonIWbuL+R5fUiO7hV7f+k/Iqoz+EFWnOJwZAs=
diff --git a/go.mod b/go.mod
index 533ef04489cc6..7f5066e134eaf 100644
--- a/go.mod
+++ b/go.mod
@@ -18,9 +18,9 @@ require (
 	github.com/aws/aws-sdk-go-v2/service/ssm v1.44.7
 	github.com/axiomhq/hyperloglog v0.0.0-20240319100328-84253e514e02
 	github.com/bradfitz/go-tool-cache v0.0.0-20260216153636-9e5201344fe5
-	github.com/bradfitz/monogok v0.0.0-20260208031948-2219c393d032
+	github.com/bradfitz/monogok v0.0.0-20260310223834-65a3d9465088
 	github.com/bramvdbogaerde/go-scp v1.4.0
-	github.com/cilium/ebpf v0.16.0
+	github.com/cilium/ebpf v0.18.0
 	github.com/coder/websocket v1.8.12
 	github.com/coreos/go-iptables v0.7.1-0.20240112124308-65c67c9f46e6
 	github.com/coreos/go-systemd v0.0.0-20191104093116-d3cd4ed1dbcf
@@ -48,6 +48,7 @@ require (
 	github.com/gokrazy/gokrazy v0.0.0-20260123094004-294c93fa173c
 	github.com/gokrazy/serial-busybox v0.0.0-20250119153030-ac58ba7574e7
 	github.com/golang/groupcache v0.0.0-20241129210726-2c02b8208cf8
+	github.com/golang/mock v1.7.0-rc.1
 	github.com/golang/snappy v0.0.4
 	github.com/golangci/golangci-lint v1.57.1
 	github.com/google/go-cmp v0.7.0
@@ -56,6 +57,7 @@ require (
 	github.com/google/gopacket v1.1.19
 	github.com/google/nftables v0.2.1-0.20240414091927-5e242ec57806
 	github.com/google/uuid v1.6.0
+	github.com/gopacket/gopacket v1.5.0
 	github.com/goreleaser/nfpm/v2 v2.33.1
 	github.com/hashicorp/go-hclog v1.6.2
 	github.com/hashicorp/raft v1.7.2
@@ -80,12 +82,13 @@ require (
 	github.com/peterbourgon/ff/v3 v3.4.0
 	github.com/pires/go-proxyproto v0.8.1
 	github.com/pkg/errors v0.9.1
-	github.com/pkg/sftp v1.13.6
+	github.com/pkg/sftp v1.13.7
 	github.com/prometheus-community/pro-bing v0.4.0
 	github.com/prometheus/client_golang v1.23.0
 	github.com/prometheus/common v0.65.0
 	github.com/prometheus/prometheus v0.49.2-0.20240125131847-c3b8ef1694ff
 	github.com/safchain/ethtool v0.3.0
+	github.com/scionproto/scion v0.14.0
 	github.com/skip2/go-qrcode v0.0.0-20200617195104-da1b6568686e
 	github.com/studio-b12/gowebdav v0.9.0
 	github.com/tailscale/certstore v0.1.1-0.20231202035212-d3fa0460f47e
@@ -122,6 +125,7 @@ require (
 	golang.org/x/tools v0.40.1-0.20260108161641-ca281cf95054
 	golang.zx2c4.com/wintun v0.0.0-20230126152724-0fa3db229ce2
 	golang.zx2c4.com/wireguard/windows v0.5.3
+	google.golang.org/grpc v1.78.0
 	gopkg.in/square/go-jose.v2 v2.6.0
 	gvisor.dev/gvisor v0.0.0-20260224225140-573d5e7127a8
 	helm.sh/helm/v3 v3.19.0
@@ -151,6 +155,7 @@ require (
 	github.com/OpenPeeDeeP/depguard/v2 v2.2.0 // indirect
 	github.com/alecthomas/go-check-sumtype v0.1.4 // indirect
 	github.com/alexkohler/nakedret/v2 v2.0.4 // indirect
+	github.com/antlr4-go/antlr/v4 v4.13.1 // indirect
 	github.com/armon/go-metrics v0.4.1 // indirect
 	github.com/asaskevich/govalidator v0.0.0-20230301143203-a9d515a09cc2 // indirect
 	github.com/beevik/ntp v0.3.0 // indirect
@@ -169,11 +174,13 @@ require (
 	github.com/containerd/platforms v1.0.0-rc.2 // indirect
 	github.com/containerd/typeurl/v2 v2.2.3 // indirect
 	github.com/cyphar/filepath-securejoin v0.6.1 // indirect
+	github.com/dchest/cmac v1.0.0 // indirect
 	github.com/deckarep/golang-set/v2 v2.8.0 // indirect
 	github.com/dgryski/go-metro v0.0.0-20180109044635-280f6062b5bc // indirect
 	github.com/docker/go-connections v0.5.0 // indirect
 	github.com/docker/go-events v0.0.0-20250808211157-605354379745 // indirect
 	github.com/docker/go-units v0.5.0 // indirect
+	github.com/dustin/go-humanize v1.0.1 // indirect
 	github.com/evanphx/json-patch v5.9.11+incompatible // indirect
 	github.com/exponent-io/jsonpath v0.0.0-20210407135951-1de76d718b3f // indirect
 	github.com/felixge/httpsnoop v1.0.4 // indirect
@@ -197,12 +204,16 @@ require (
 	github.com/gorilla/websocket v1.5.4-0.20250319132907-e064f32e3674 // indirect
 	github.com/gosuri/uitable v0.0.4 // indirect
 	github.com/gregjones/httpcache v0.0.0-20190611155906-901d90724c79 // indirect
+	github.com/grpc-ecosystem/go-grpc-middleware v1.4.0 // indirect
+	github.com/grpc-ecosystem/go-grpc-prometheus v1.2.0 // indirect
+	github.com/grpc-ecosystem/grpc-opentracing v0.0.0-20180507213350-8e809c8a8645 // indirect
 	github.com/hashicorp/errwrap v1.1.0 // indirect
 	github.com/hashicorp/go-immutable-radix v1.3.1 // indirect
 	github.com/hashicorp/go-metrics v0.5.4 // indirect
 	github.com/hashicorp/go-msgpack/v2 v2.1.2 // indirect
 	github.com/hashicorp/go-multierror v1.1.1 // indirect
 	github.com/hashicorp/golang-lru v0.6.0 // indirect
+	github.com/iancoleman/strcase v0.3.0 // indirect
 	github.com/jjti/go-spancheck v0.5.3 // indirect
 	github.com/jmoiron/sqlx v1.4.0 // indirect
 	github.com/josharian/native v1.1.0 // indirect
@@ -224,16 +235,26 @@ require (
 	github.com/moby/term v0.5.2 // indirect
 	github.com/monochromegane/go-gitignore v0.0.0-20200626010858-205db1a8cc00 // indirect
 	github.com/mxk/go-flowrate v0.0.0-20140419014527-cca7078d478f // indirect
+	github.com/ncruces/go-strftime v0.1.9 // indirect
+	github.com/olekukonko/errors v0.0.0-20250405072817-4e6d85265da6 // indirect
+	github.com/olekukonko/ll v0.0.8 // indirect
+	github.com/opentracing/opentracing-go v1.2.0 // indirect
+	github.com/patrickmn/go-cache v2.1.1-0.20180815053127-5633e0862627+incompatible // indirect
 	github.com/pelletier/go-toml v1.9.5 // indirect
 	github.com/peterbourgon/diskv v2.0.1+incompatible // indirect
 	github.com/planetscale/vtprotobuf v0.6.1-0.20240319094008-0393e58bdf10 // indirect
 	github.com/puzpuzpuz/xsync v1.5.2 // indirect
+	github.com/remyoudompheng/bigfft v0.0.0-20230129092748-24d4a6f8daec // indirect
 	github.com/rtr7/dhcp4 v0.0.0-20220302171438-18c84d089b46 // indirect
 	github.com/rubenv/sql-migrate v1.8.0 // indirect
 	github.com/russross/blackfriday/v2 v2.1.0 // indirect
+	github.com/sagikazarmark/locafero v0.7.0 // indirect
 	github.com/santhosh-tekuri/jsonschema/v5 v5.3.1 // indirect
 	github.com/santhosh-tekuri/jsonschema/v6 v6.0.2 // indirect
+	github.com/sourcegraph/conc v0.3.0 // indirect
 	github.com/stacklok/frizbee v0.1.7 // indirect
+	github.com/uber/jaeger-client-go v2.30.0+incompatible // indirect
+	github.com/uber/jaeger-lib v2.4.1+incompatible // indirect
 	github.com/vishvananda/netlink v1.3.1-0.20240922070040-084abd93d350 // indirect
 	github.com/xen0n/gosmopolitan v1.2.2 // indirect
 	github.com/xlab/treeprint v1.2.0 // indirect
@@ -246,6 +267,7 @@ require (
 	go.opentelemetry.io/otel v1.39.0 // indirect
 	go.opentelemetry.io/otel/metric v1.39.0 // indirect
 	go.opentelemetry.io/otel/trace v1.39.0 // indirect
+	go.uber.org/atomic v1.11.0 // indirect
 	go.uber.org/automaxprocs v1.5.3 // indirect
 	go.yaml.in/yaml/v2 v2.4.2 // indirect
 	go.yaml.in/yaml/v3 v3.0.4 // indirect
@@ -255,16 +277,20 @@ require (
 	golang.org/x/xerrors v0.0.0-20240716161551-93cc26a95ae9 // indirect
 	google.golang.org/genproto/googleapis/api v0.0.0-20251213004720-97cd9d5aeac2 // indirect
 	google.golang.org/genproto/googleapis/rpc v0.0.0-20251222181119-0a764e51fe1b // indirect
-	google.golang.org/grpc v1.78.0 // indirect
 	gopkg.in/evanphx/json-patch.v4 v4.12.0 // indirect
 	k8s.io/cli-runtime v0.34.0 // indirect
 	k8s.io/component-base v0.34.0 // indirect
 	k8s.io/kubectl v0.34.0 // indirect
+	modernc.org/libc v1.66.3 // indirect
+	modernc.org/mathutil v1.7.1 // indirect
+	modernc.org/memory v1.11.0 // indirect
+	modernc.org/sqlite v1.39.0 // indirect
 	oras.land/oras-go/v2 v2.6.0 // indirect
 	sigs.k8s.io/kustomize/api v0.20.1 // indirect
 	sigs.k8s.io/kustomize/kyaml v0.20.1 // indirect
 	sigs.k8s.io/randfill v1.0.0 // indirect
 	sigs.k8s.io/structured-merge-diff/v6 v6.3.0 // indirect
+	zgo.at/zcache/v2 v2.1.0 // indirect
 )
 
 require (
@@ -368,7 +394,6 @@ require (
 	github.com/gostaticanalysis/forcetypeassert v0.1.0 // indirect
 	github.com/gostaticanalysis/nilerr v0.1.1 // indirect
 	github.com/hashicorp/go-version v1.6.0 // indirect
-	github.com/hashicorp/hcl v1.0.0 // indirect
 	github.com/hexops/gotextdiff v1.0.3 // indirect
 	github.com/huandu/xstrings v1.5.0 // indirect
 	github.com/imdario/mergo v0.3.16 // indirect
@@ -395,17 +420,15 @@ require (
 	github.com/ldez/tagliatelle v0.5.0 // indirect
 	github.com/leonklingele/grouper v1.1.1 // indirect
 	github.com/lufeee/execinquery v1.2.1 // indirect
-	github.com/magiconair/properties v1.8.7 // indirect
 	github.com/mailru/easyjson v0.7.7 // indirect
 	github.com/maratori/testableexamples v1.0.0 // indirect
 	github.com/maratori/testpackage v1.1.1 // indirect
 	github.com/matoous/godox v0.0.0-20230222163458-006bad1f9d26 // indirect
-	github.com/mattn/go-runewidth v0.0.14 // indirect
-	github.com/mdlayher/socket v0.5.0
+	github.com/mattn/go-runewidth v0.0.16 // indirect
+	github.com/mdlayher/socket v0.5.1
 	github.com/mgechev/revive v1.3.7 // indirect
 	github.com/mitchellh/copystructure v1.2.0 // indirect
 	github.com/mitchellh/go-homedir v1.1.0 // indirect
-	github.com/mitchellh/mapstructure v1.5.0 // indirect
 	github.com/mitchellh/reflectwalk v1.0.2 // indirect
 	github.com/modern-go/concurrent v0.0.0-20180306012644-bacd9c7ef1dd // indirect
 	github.com/modern-go/reflect2 v1.0.3-0.20250322232337-35a7c28c31ee // indirect
@@ -416,10 +439,10 @@ require (
 	github.com/nishanths/exhaustive v0.12.0 // indirect
 	github.com/nishanths/predeclared v0.2.2 // indirect
 	github.com/nunnatsa/ginkgolinter v0.16.1 // indirect
-	github.com/olekukonko/tablewriter v0.0.5 // indirect
+	github.com/olekukonko/tablewriter v1.0.7 // indirect
 	github.com/opencontainers/go-digest v1.0.0 // indirect
 	github.com/opencontainers/image-spec v1.1.1 // indirect
-	github.com/pelletier/go-toml/v2 v2.2.0 // indirect
+	github.com/pelletier/go-toml/v2 v2.2.4 // indirect
 	github.com/pierrec/lz4/v4 v4.1.25 // indirect
 	github.com/pjbgf/sha1cd v0.3.2 // indirect
 	github.com/pkg/diff v0.0.0-20210226163009-20ebb0f2a09e // indirect
@@ -431,7 +454,7 @@ require (
 	github.com/quasilyte/gogrep v0.5.0 // indirect
 	github.com/quasilyte/regex/syntax v0.0.0-20210819130434-b3f0c404a727 // indirect
 	github.com/quasilyte/stdinfo v0.0.0-20220114132959-f7386bf02567 // indirect
-	github.com/rivo/uniseg v0.4.4 // indirect
+	github.com/rivo/uniseg v0.4.7 // indirect
 	github.com/rogpeppe/go-internal v1.14.1 // indirect
 	github.com/ryancurrah/gomodguard v1.3.1 // indirect
 	github.com/ryanrolds/sqlclosecheck v0.5.1 // indirect
@@ -448,17 +471,16 @@ require (
 	github.com/skeema/knownhosts v1.3.1 // indirect
 	github.com/sonatard/noctx v0.0.2 // indirect
 	github.com/sourcegraph/go-diff v0.7.0 // indirect
-	github.com/spf13/afero v1.11.0 // indirect
-	github.com/spf13/cast v1.7.0 // indirect
+	github.com/spf13/afero v1.12.0 // indirect
+	github.com/spf13/cast v1.7.1 // indirect
 	github.com/spf13/cobra v1.10.2 // indirect
-	github.com/spf13/jwalterweatherman v1.1.0 // indirect
 	github.com/spf13/pflag v1.0.9 // indirect
-	github.com/spf13/viper v1.16.0 // indirect
+	github.com/spf13/viper v1.20.1 // indirect
 	github.com/ssgreg/nlreturn/v2 v2.2.1 // indirect
 	github.com/stbenjam/no-sprintf-host-port v0.1.1 // indirect
 	github.com/stretchr/objx v0.5.2 // indirect
 	github.com/stretchr/testify v1.11.1
-	github.com/subosito/gotenv v1.4.2 // indirect
+	github.com/subosito/gotenv v1.6.0 // indirect
 	github.com/t-yuki/gocover-cobertura v0.0.0-20180217150009-aaee18c8195c // indirect
 	github.com/tailscale/go-winio v0.0.0-20231025203758-c4f33415bf55
 	github.com/tdakkota/asciicheck v0.2.0 // indirect
@@ -486,7 +508,6 @@ require (
 	gomodules.xyz/jsonpatch/v2 v2.4.0 // indirect
 	google.golang.org/protobuf v1.36.11 // indirect
 	gopkg.in/inf.v0 v0.9.1 // indirect
-	gopkg.in/ini.v1 v1.67.0 // indirect
 	gopkg.in/warnings.v0 v0.1.2 // indirect
 	gopkg.in/yaml.v2 v2.4.0 // indirect
 	gopkg.in/yaml.v3 v3.0.1
diff --git a/go.mod.sri b/go.mod.sri
index 0e0a6fdece5ee..ab47b01f02f07 100644
--- a/go.mod.sri
+++ b/go.mod.sri
@@ -1 +1 @@
-sha256-dx+SJyDx+eZptFaMatoyM6w1E3nJKY+hKs7nuR997bE=
+sha256-V4vJ1MonIWbuL+R5fUiO7hV7f+k/Iqoz+EFWnOJwZAs=
diff --git a/go.sum b/go.sum
index 48b1e9379006f..c05ba56064910 100644
--- a/go.sum
+++ b/go.sum
@@ -77,6 +77,8 @@ github.com/Djarvur/go-err113 v0.1.0 h1:uCRZZOdMQ0TZPHYTdYpoC0bLYJKPEHPUJ8MeAa51l
 github.com/Djarvur/go-err113 v0.1.0/go.mod h1:4UJr5HIiMZrwgkSPdsjy2uOQExX/WEILpIrO9UPGuXs=
 github.com/GaijinEntertainment/go-exhaustruct/v3 v3.2.0 h1:sATXp1x6/axKxz2Gjxv8MALP0bXaNRfQinEwyfMcx8c=
 github.com/GaijinEntertainment/go-exhaustruct/v3 v3.2.0/go.mod h1:Nl76DrGNJTA1KJ0LePKBw/vznBX1EHbAZX8mwjR82nI=
+github.com/HdrHistogram/hdrhistogram-go v1.1.2 h1:5IcZpTvzydCQeHzK4Ef/D5rrSqwxob0t8PQPMybUNFM=
+github.com/HdrHistogram/hdrhistogram-go v1.1.2/go.mod h1:yDgFjdqOqDEKOvasDdhWNXYg9BVp4O+o5f6V/ehm6Oo=
 github.com/Kodeworks/golang-image-ico v0.0.0-20141118225523-73f0f4cfade9 h1:1ltqoej5GtaWF8jaiA49HwsZD459jqm9YFz9ZtMFpQA=
 github.com/Kodeworks/golang-image-ico v0.0.0-20141118225523-73f0f4cfade9/go.mod h1:7uhhqiBaR4CpN0k9rMjOtjpcfGd6DG2m04zQxKnWQ0I=
 github.com/MakeNowJust/heredoc v1.0.0 h1:cXCdzVdstXyiTqTvfqk9SDHpKNjxuom+DOlyEeQ4pzQ=
@@ -129,6 +131,8 @@ github.com/andybalholm/brotli v1.1.0 h1:eLKJA0d02Lf0mVpIDgYnqXcUn0GqVmEFny3VuID1
 github.com/andybalholm/brotli v1.1.0/go.mod h1:sms7XGricyQI9K10gOSf56VKKWS4oLer58Q+mhRPtnY=
 github.com/anmitsu/go-shlex v0.0.0-20200514113438-38f4b401e2be h1:9AeTilPcZAjCFIImctFaOjnTIavg87rW78vTPkQqLI8=
 github.com/anmitsu/go-shlex v0.0.0-20200514113438-38f4b401e2be/go.mod h1:ySMOLuWl6zY27l47sB3qLNK6tF2fkHG55UZxx8oIVo4=
+github.com/antlr4-go/antlr/v4 v4.13.1 h1:SqQKkuVZ+zWkMMNkjy5FZe5mr5WURWnlpmOuzYWrPrQ=
+github.com/antlr4-go/antlr/v4 v4.13.1/go.mod h1:GKmUxMtwp6ZgGwZSva4eWPC5mS6vUAmOABFgjdkM7Nw=
 github.com/armon/go-metrics v0.4.1 h1:hR91U9KYmb6bLBYLQjyM+3j+rcd/UhE+G78SFnF8gJA=
 github.com/armon/go-metrics v0.4.1/go.mod h1:E6amYzXo6aW1tqzoZGT755KkbgrJsSdpwZ+3JqfkOG4=
 github.com/armon/go-proxyproto v0.0.0-20210323213023-7e956b284f0a/go.mod h1:QmP9hvJ91BbJmGVGSbutW19IC0Q9phDCLGaomwTJbgU=
@@ -187,6 +191,7 @@ github.com/axiomhq/hyperloglog v0.0.0-20240319100328-84253e514e02/go.mod h1:k08r
 github.com/beevik/ntp v0.2.0/go.mod h1:hIHWr+l3+/clUnF44zdK+CWW7fO8dR5cIylAQ76NRpg=
 github.com/beevik/ntp v0.3.0 h1:xzVrPrE4ziasFXgBVBZJDP0Wg/KpMwk2KHJ4Ba8GrDw=
 github.com/beevik/ntp v0.3.0/go.mod h1:hIHWr+l3+/clUnF44zdK+CWW7fO8dR5cIylAQ76NRpg=
+github.com/benbjohnson/clock v1.1.0/go.mod h1:J11/hYXuz8f4ySSvYwY0FKfm+ezbsZBKZxNJlLklBHA=
 github.com/beorn7/perks v0.0.0-20180321164747-3a771d992973/go.mod h1:Dwedo/Wpr24TaqPxmxbtue+5NUziq4I4S80YR8gNf3Q=
 github.com/beorn7/perks v1.0.0/go.mod h1:KWe93zE9D1o94FZ5RNwFwVgaQK1VOXiVxmqh+CedLV8=
 github.com/beorn7/perks v1.0.1 h1:VlbKKnNfV8bJzeqoa4cOKqO6bYr3WgKZxO8Z16+hsOM=
@@ -205,8 +210,8 @@ github.com/bombsimon/wsl/v4 v4.2.1 h1:Cxg6u+XDWff75SIFFmNsqnIOgob+Q9hG6y/ioKbRFi
 github.com/bombsimon/wsl/v4 v4.2.1/go.mod h1:Xu/kDxGZTofQcDGCtQe9KCzhHphIe0fDuyWTxER9Feo=
 github.com/bradfitz/go-tool-cache v0.0.0-20260216153636-9e5201344fe5 h1:0sG3c7afYdBNlc3QyhckvZ4bV9iqlfqCQM1i+mWm0eE=
 github.com/bradfitz/go-tool-cache v0.0.0-20260216153636-9e5201344fe5/go.mod h1:78ZLITnBUCDJeU01+wYYJKaPYYgsDzJPRfxeI8qFh5g=
-github.com/bradfitz/monogok v0.0.0-20260208031948-2219c393d032 h1:xDomVqO85ss/98Ky5zxM/g86bXDNBLebM2I9G/fu6uA=
-github.com/bradfitz/monogok v0.0.0-20260208031948-2219c393d032/go.mod h1:TG1HbU9fRVDnNgXncVkKz9GdvjIvqquXjH6QZSEVmY4=
+github.com/bradfitz/monogok v0.0.0-20260310223834-65a3d9465088 h1:dDVY5cJ+7bQQll29aeWGx1Ima4RIGy/f1fXVs+HlIxo=
+github.com/bradfitz/monogok v0.0.0-20260310223834-65a3d9465088/go.mod h1:TG1HbU9fRVDnNgXncVkKz9GdvjIvqquXjH6QZSEVmY4=
 github.com/bramvdbogaerde/go-scp v1.4.0 h1:jKMwpwCbcX1KyvDbm/PDJuXcMuNVlLGi0Q0reuzjyKY=
 github.com/bramvdbogaerde/go-scp v1.4.0/go.mod h1:on2aH5AxaFb2G0N5Vsdy6B0Ml7k9HuHSwfo1y0QzAbQ=
 github.com/breml/bidichk v0.2.7 h1:dAkKQPLl/Qrk7hnP6P+E0xOodrq8Us7+U0o4UBOAlQY=
@@ -246,8 +251,8 @@ github.com/chavacava/garif v0.1.0/go.mod h1:XMyYCkEL58DF0oyW4qDjjnPWONs2HBqYKI+U
 github.com/chzyer/logex v1.1.10/go.mod h1:+Ywpsq7O8HXn0nuIou7OrIPyXbp3wmkHB+jjWRnGsAI=
 github.com/chzyer/readline v0.0.0-20180603132655-2972be24d48e/go.mod h1:nSuG5e5PlCu98SY8svDHJxuZscDgtXS6KTTbou5AhLI=
 github.com/chzyer/test v0.0.0-20180213035817-a1ea475d72b1/go.mod h1:Q3SI9o4m/ZMnBNeIyt5eFwwo7qiLfzFZmjNmxjkiQlU=
-github.com/cilium/ebpf v0.16.0 h1:+BiEnHL6Z7lXnlGUsXQPPAE7+kenAd4ES8MQ5min0Ok=
-github.com/cilium/ebpf v0.16.0/go.mod h1:L7u2Blt2jMM/vLAVgjxluxtBKlz3/GWjB0dMOEngfwE=
+github.com/cilium/ebpf v0.18.0 h1:OsSwqS4y+gQHxaKgg2U/+Fev834kdnsQbtzRnbVC6Gs=
+github.com/cilium/ebpf v0.18.0/go.mod h1:vmsAT73y4lW2b4peE+qcOqw6MxvWQdC+LiU5gd/xyo4=
 github.com/circonus-labs/circonus-gometrics v2.3.1+incompatible/go.mod h1:nmEj6Dob7S7YxXgwXpfOuvO54S+tGdZdw9fuRZt25Ag=
 github.com/circonus-labs/circonusllhist v0.1.3/go.mod h1:kMXHVDlOchFAehlya5ePtbp5jckzBHf4XRpQvBOLI+I=
 github.com/ckaznocha/intrange v0.1.0 h1:ZiGBhvrdsKpoEfzh9CjBfDSZof6QB0ORY5tXasUtiew=
@@ -301,6 +306,8 @@ github.com/davecgh/go-spew v1.1.2-0.20180830191138-d8f796af33cc h1:U9qPSI2PIWSS1
 github.com/davecgh/go-spew v1.1.2-0.20180830191138-d8f796af33cc/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/dblohm7/wingoes v0.0.0-20240119213807-a09d6be7affa h1:h8TfIT1xc8FWbwwpmHn1J5i43Y0uZP97GqasGCzSRJk=
 github.com/dblohm7/wingoes v0.0.0-20240119213807-a09d6be7affa/go.mod h1:Nx87SkVqTKd8UtT+xu7sM/l+LgXs6c0aHrlKusR+2EQ=
+github.com/dchest/cmac v1.0.0 h1:Vaorm9FVpO2P+YmRdH0RVCUB1XF3Ge1yg9scPvJphyk=
+github.com/dchest/cmac v1.0.0/go.mod h1:0zViPqHm8iZwwMl1cuK3HqK7Tu4Q7DV4EuMIOUwBVQ0=
 github.com/deckarep/golang-set/v2 v2.8.0 h1:swm0rlPCmdWn9mESxKOjWk8hXSqoxOp+ZlfuyaAdFlQ=
 github.com/deckarep/golang-set/v2 v2.8.0/go.mod h1:VAky9rY/yGXJOLEDv3OMci+7wtDpOF4IN+y82NBOac4=
 github.com/denis-tingaikin/go-header v0.5.0 h1:SRdnP5ZKvcO9KKRP1KJrhFR3RrlGuD+42t4429eC9k8=
@@ -337,6 +344,8 @@ github.com/docker/go-units v0.5.0 h1:69rxXcBk27SvSaaxTtLh/8llcHD8vYHT7WSdRZ/jvr4
 github.com/docker/go-units v0.5.0/go.mod h1:fgPhTUdO+D/Jk86RDLlptpiXQzgHJF7gydDDbaIK4Dk=
 github.com/dsnet/try v0.0.3 h1:ptR59SsrcFUYbT/FhAbKTV6iLkeD6O18qfIWRml2fqI=
 github.com/dsnet/try v0.0.3/go.mod h1:WBM8tRpUmnXXhY1U6/S8dt6UWdHTQ7y8A5YSkRCkq40=
+github.com/dustin/go-humanize v1.0.1 h1:GzkhY7T5VNhEkwH0PVJgjz+fX1rhBrR7pRT3mDkpeCY=
+github.com/dustin/go-humanize v1.0.1/go.mod h1:Mu1zIs6XwVuF/gI1OepvI0qD18qycQx+mFykh5fBlto=
 github.com/elastic/crd-ref-docs v0.0.12 h1:F3seyncbzUz3rT3d+caeYWhumb5ojYQ6Bl0Z+zOp16M=
 github.com/elastic/crd-ref-docs v0.0.12/go.mod h1:X83mMBdJt05heJUYiS3T0yJ/JkCuliuhSUNav5Gjo/U=
 github.com/elazarl/goproxy v1.7.2 h1:Y2o6urb7Eule09PjlhQRGNsqRfPmYI3KKQLFpCAV3+o=
@@ -436,8 +445,8 @@ github.com/go-playground/universal-translator v0.17.0 h1:icxd5fm+REJzpZx7ZfpaD87
 github.com/go-playground/universal-translator v0.17.0/go.mod h1:UkSxE5sNxxRwHyU+Scu5vgOQjsIJAF8j9muTVoKLVtA=
 github.com/go-playground/validator/v10 v10.4.1 h1:pH2c5ADXtd66mxoE0Zm9SUhxE20r7aM3F26W0hOn+GE=
 github.com/go-playground/validator/v10 v10.4.1/go.mod h1:nlOn6nFhuKACm19sB/8EGNn9GlaMV7XkbRSipzJ0Ii4=
-github.com/go-quicktest/qt v1.101.0 h1:O1K29Txy5P2OK0dGo59b7b0LR6wKfIhttaAhHUyn7eI=
-github.com/go-quicktest/qt v1.101.0/go.mod h1:14Bz/f7NwaXPtdYEgzsx46kqSxVwTbzVZsDC26tQJow=
+github.com/go-quicktest/qt v1.101.1-0.20240301121107-c6c8733fa1e6 h1:teYtXy9B7y5lHTp8V9KPxpYRAVA7dozigQcMiBust1s=
+github.com/go-quicktest/qt v1.101.1-0.20240301121107-c6c8733fa1e6/go.mod h1:p4lGIVX+8Wa6ZPNDvqcxq36XpUDLh42FLetFU7odllI=
 github.com/go-sql-driver/mysql v1.8.1 h1:LedoTUt/eveggdHS9qUFC1EFSa8bU2+1pZjSRpvNJ1Y=
 github.com/go-sql-driver/mysql v1.8.1/go.mod h1:wEBSXgmK//2ZFJyE+qWnIsVGmvmEKlqwuVSjsCm7DZg=
 github.com/go-stack/stack v1.8.0/go.mod h1:v0f6uXyyMGvRgIKkXu+yp6POWl0qKG85gN/melR3HDY=
@@ -509,6 +518,8 @@ github.com/golang/mock v1.4.0/go.mod h1:UOMv5ysSaYNkG+OFQykRIcU/QvvxJf3p21QfJ2Bt
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@@ -593,8 +604,8 @@ github.com/google/pprof v0.0.0-20200212024743-f11f1df84d12/go.mod h1:ZgVRPoUq/hf
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@@ -606,6 +617,8 @@ github.com/google/uuid v1.6.0 h1:NIvaJDMOsjHA8n1jAhLSgzrAzy1Hgr+hNrb57e+94F0=
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@@ -642,9 +655,15 @@ github.com/gosuri/uitable v0.0.4 h1:IG2xLKRvErL3uhY6e1BylFzG+aJiwQviDDTfOKeKTpY=
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@@ -674,12 +693,10 @@ github.com/hashicorp/golang-lru v0.5.0/go.mod h1:/m3WP610KZHVQ1SGc6re/UDhFvYD7pJ
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@@ -696,6 +713,8 @@ github.com/hugelgupf/vmtest v0.0.0-20240216064925-0561770280a1 h1:jWoR2Yqg8tzM0v
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@@ -811,8 +830,6 @@ github.com/lufeee/execinquery v1.2.1 h1:hf0Ems4SHcUGBxpGN7Jz78z1ppVkP/837ZlETPCE
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@@ -832,9 +849,8 @@ github.com/mattn/go-isatty v0.0.14/go.mod h1:7GGIvUiUoEMVVmxf/4nioHXj79iQHKdU27k
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@@ -847,8 +863,8 @@ github.com/mdlayher/packet v1.1.2/go.mod h1:GEu1+n9sG5VtiRE4SydOmX5GTwyyYlteZiFU
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@@ -863,8 +879,6 @@ github.com/mitchellh/go-ps v1.0.0 h1:i6ampVEEF4wQFF+bkYfwYgY+F/uYJDktmvLPf7qIgjc
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@@ -901,6 +915,8 @@ github.com/mxk/go-flowrate v0.0.0-20140419014527-cca7078d478f h1:y5//uYreIhSUg3J
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@@ -911,8 +927,12 @@ github.com/nunnatsa/ginkgolinter v0.16.1 h1:uDIPSxgVHZ7PgbJElRDGzymkXH+JaF7mjew+
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 github.com/ulikunitz/xz v0.5.15/go.mod h1:nbz6k7qbPmH4IRqmfOplQw/tblSgqTqBwxkY0oWt/14=
 github.com/ultraware/funlen v0.1.0 h1:BuqclbkY6pO+cvxoq7OsktIXZpgBSkYTQtmwhAK81vI=
@@ -1289,12 +1325,20 @@ go.opentelemetry.io/otel/trace v1.39.0 h1:2d2vfpEDmCJ5zVYz7ijaJdOF59xLomrvj7bjt6
 go.opentelemetry.io/otel/trace v1.39.0/go.mod h1:88w4/PnZSazkGzz/w84VHpQafiU4EtqqlVdxWy+rNOA=
 go.opentelemetry.io/proto/otlp v1.5.0 h1:xJvq7gMzB31/d406fB8U5CBdyQGw4P399D1aQWU/3i4=
 go.opentelemetry.io/proto/otlp v1.5.0/go.mod h1:keN8WnHxOy8PG0rQZjJJ5A2ebUoafqWp0eVQ4yIXvJ4=
+go.uber.org/atomic v1.7.0/go.mod h1:fEN4uk6kAWBTFdckzkM89CLk9XfWZrxpCo0nPH17wJc=
+go.uber.org/atomic v1.11.0 h1:ZvwS0R+56ePWxUNi+Atn9dWONBPp/AUETXlHW0DxSjE=
+go.uber.org/atomic v1.11.0/go.mod h1:LUxbIzbOniOlMKjJjyPfpl4v+PKK2cNJn91OQbhoJI0=
 go.uber.org/automaxprocs v1.5.3 h1:kWazyxZUrS3Gs4qUpbwo5kEIMGe/DAvi5Z4tl2NW4j8=
 go.uber.org/automaxprocs v1.5.3/go.mod h1:eRbA25aqJrxAbsLO0xy5jVwPt7FQnRgjW+efnwa1WM0=
+go.uber.org/goleak v1.1.10/go.mod h1:8a7PlsEVH3e/a/GLqe5IIrQx6GzcnRmZEufDUTk4A7A=
 go.uber.org/goleak v1.3.0 h1:2K3zAYmnTNqV73imy9J1T3WC+gmCePx2hEGkimedGto=
 go.uber.org/goleak v1.3.0/go.mod h1:CoHD4mav9JJNrW/WLlf7HGZPjdw8EucARQHekz1X6bE=
+go.uber.org/mock v0.5.2 h1:LbtPTcP8A5k9WPXj54PPPbjcI4Y6lhyOZXn+VS7wNko=
+go.uber.org/mock v0.5.2/go.mod h1:wLlUxC2vVTPTaE3UD51E0BGOAElKrILxhVSDYQLld5o=
+go.uber.org/multierr v1.6.0/go.mod h1:cdWPpRnG4AhwMwsgIHip0KRBQjJy5kYEpYjJxpXp9iU=
 go.uber.org/multierr v1.11.0 h1:blXXJkSxSSfBVBlC76pxqeO+LN3aDfLQo+309xJstO0=
 go.uber.org/multierr v1.11.0/go.mod h1:20+QtiLqy0Nd6FdQB9TLXag12DsQkrbs3htMFfDN80Y=
+go.uber.org/zap v1.18.1/go.mod h1:xg/QME4nWcxGxrpdeYfq7UvYrLh66cuVKdrbD1XF/NI=
 go.uber.org/zap v1.27.0 h1:aJMhYGrd5QSmlpLMr2MftRKl7t8J8PTZPA732ud/XR8=
 go.uber.org/zap v1.27.0/go.mod h1:GB2qFLM7cTU87MWRP2mPIjqfIDnGu+VIO4V/SdhGo2E=
 go.yaml.in/yaml/v2 v2.4.2 h1:DzmwEr2rDGHl7lsFgAHxmNz/1NlQ7xLIrlN2h5d1eGI=
@@ -1315,6 +1359,7 @@ golang.org/x/crypto v0.0.0-20200622213623-75b288015ac9/go.mod h1:LzIPMQfyMNhhGPh
 golang.org/x/crypto v0.0.0-20210921155107-089bfa567519/go.mod h1:GvvjBRRGRdwPK5ydBHafDWAxML/pGHZbMvKqRZ5+Abc=
 golang.org/x/crypto v0.0.0-20220622213112-05595931fe9d/go.mod h1:IxCIyHEi3zRg3s0A5j5BB6A9Jmi73HwBIUl50j+osU4=
 golang.org/x/crypto v0.1.0/go.mod h1:RecgLatLF4+eUMCP1PoPZQb+cVrJcOPbHkTkbkB9sbw=
+golang.org/x/crypto v0.17.0/go.mod h1:gCAAfMLgwOJRpTjQ2zCCt2OcSfYMTeZVSRtQlPC7Nq4=
 golang.org/x/crypto v0.46.0 h1:cKRW/pmt1pKAfetfu+RCEvjvZkA9RimPbh7bhFjGVBU=
 golang.org/x/crypto v0.46.0/go.mod h1:Evb/oLKmMraqjZ2iQTwDwvCtJkczlDuTmdJXoZVzqU0=
 golang.org/x/crypto/x509roots/fallback v0.0.0-20260113154411-7d0074ccc6f1 h1:EBHQuS9qI8xJ96+YRgVV2ahFLUYbWpt1rf3wPfXN2wQ=
@@ -1407,6 +1452,7 @@ golang.org/x/net v0.1.0/go.mod h1:Cx3nUiGt4eDBEyega/BKRp+/AlGL8hYe7U9odMt2Cco=
 golang.org/x/net v0.2.0/go.mod h1:KqCZLdyyvdV855qA2rE3GC2aiw5xGR5TEjj8smXukLY=
 golang.org/x/net v0.5.0/go.mod h1:DivGGAXEgPSlEBzxGzZI+ZLohi+xUj054jfeKui00ws=
 golang.org/x/net v0.6.0/go.mod h1:2Tu9+aMcznHK/AK1HMvgo6xiTLG5rD5rZLDS+rp2Bjs=
+golang.org/x/net v0.10.0/go.mod h1:0qNGK6F8kojg2nk9dLZ2mShWaEBan6FAoqfSigmmuDg=
 golang.org/x/net v0.48.0 h1:zyQRTTrjc33Lhh0fBgT/H3oZq9WuvRR5gPC70xpDiQU=
 golang.org/x/net v0.48.0/go.mod h1:+ndRgGjkh8FGtu1w1FGbEC31if4VrNVMuKTgcAAnQRY=
 golang.org/x/oauth2 v0.0.0-20180821212333-d2e6202438be/go.mod h1:N/0e6XlmueqKjAGxoOufVs8QHGRruUQn6yWY3a++T0U=
@@ -1481,6 +1527,7 @@ golang.org/x/sys v0.0.0-20210616094352-59db8d763f22/go.mod h1:oPkhp1MJrh7nUepCBc
 golang.org/x/sys v0.0.0-20210630005230-0f9fa26af87c/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.0.0-20210927094055-39ccf1dd6fa6/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.0.0-20211019181941-9d821ace8654/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.0.0-20211025201205-69cdffdb9359/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.0.0-20211105183446-c75c47738b0c/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.0.0-20220114195835-da31bd327af9/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.0.0-20220503163025-988cb79eb6c6/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
@@ -1496,7 +1543,9 @@ golang.org/x/sys v0.2.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.4.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.5.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.6.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.8.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.10.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.15.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
 golang.org/x/sys v0.40.0 h1:DBZZqJ2Rkml6QMQsZywtnjnnGvHza6BTfYFWY9kjEWQ=
 golang.org/x/sys v0.40.0/go.mod h1:OgkHotnGiDImocRcuBABYBEXf8A9a87e/uXjp9XT3ks=
 golang.org/x/telemetry v0.0.0-20251203150158-8fff8a5912fc h1:bH6xUXay0AIFMElXG2rQ4uiE+7ncwtiOdPfYK1NK2XA=
@@ -1507,6 +1556,8 @@ golang.org/x/term v0.1.0/go.mod h1:jbD1KX2456YbFQfuXm/mYQcufACuNUgVhRMnK/tPxf8=
 golang.org/x/term v0.2.0/go.mod h1:TVmDHMZPmdnySmBfhjOoOdhjzdE1h4u1VwSiw2l1Nuc=
 golang.org/x/term v0.4.0/go.mod h1:9P2UbLfCdcvo3p/nzKvsmas4TnlujnuoV9hGgYzW1lQ=
 golang.org/x/term v0.5.0/go.mod h1:jMB1sMXY+tzblOD4FWmEbocvup2/aLOaQEp7JmGp78k=
+golang.org/x/term v0.8.0/go.mod h1:xPskH00ivmX89bAKVGSKKtLOWNx2+17Eiy94tnKShWo=
+golang.org/x/term v0.15.0/go.mod h1:BDl952bC7+uMoWR75FIrCDx79TPU9oHkTZ9yRbYOrX0=
 golang.org/x/term v0.38.0 h1:PQ5pkm/rLO6HnxFR7N2lJHOZX6Kez5Y1gDSJla6jo7Q=
 golang.org/x/term v0.38.0/go.mod h1:bSEAKrOT1W+VSu9TSCMtoGEOUcKxOKgl3LE5QEF/xVg=
 golang.org/x/text v0.0.0-20170915032832-14c0d48ead0c/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
@@ -1519,6 +1570,8 @@ golang.org/x/text v0.3.7/go.mod h1:u+2+/6zg+i71rQMx5EYifcz6MCKuco9NR6JIITiCfzQ=
 golang.org/x/text v0.4.0/go.mod h1:mrYo+phRRbMaCq/xk9113O4dZlRixOauAjOtrjsXDZ8=
 golang.org/x/text v0.6.0/go.mod h1:mrYo+phRRbMaCq/xk9113O4dZlRixOauAjOtrjsXDZ8=
 golang.org/x/text v0.7.0/go.mod h1:mrYo+phRRbMaCq/xk9113O4dZlRixOauAjOtrjsXDZ8=
+golang.org/x/text v0.9.0/go.mod h1:e1OnstbJyHTd6l/uOt8jFFHp6TRDWZR/bV3emEE/zU8=
+golang.org/x/text v0.14.0/go.mod h1:18ZOQIKpY8NJVqYksKHtTdi31H5itFRjB5/qKTNYzSU=
 golang.org/x/text v0.32.0 h1:ZD01bjUt1FQ9WJ0ClOL5vxgxOI/sVCNgX1YtKwcY0mU=
 golang.org/x/text v0.32.0/go.mod h1:o/rUWzghvpD5TXrTIBuJU77MTaN0ljMWE47kxGJQ7jY=
 golang.org/x/time v0.0.0-20181108054448-85acf8d2951c/go.mod h1:tRJNPiyCQ0inRvYxbN9jk5I+vvW/OXSQhTDSoE431IQ=
@@ -1582,6 +1635,7 @@ golang.org/x/tools v0.1.1-0.20210205202024-ef80cdb6ec6d/go.mod h1:9bzcO0MWcOuT0t
 golang.org/x/tools v0.1.1-0.20210302220138-2ac05c832e1a/go.mod h1:9bzcO0MWcOuT0tm1iBGzDVPshzfwoVvREIui8C+MHqU=
 golang.org/x/tools v0.1.1/go.mod h1:o0xws9oXOQQZyjljx8fwUC0k7L1pTE6eaCbjGeHmOkk=
 golang.org/x/tools v0.1.5/go.mod h1:o0xws9oXOQQZyjljx8fwUC0k7L1pTE6eaCbjGeHmOkk=
+golang.org/x/tools v0.1.8/go.mod h1:nABZi5QlRsZVlzPpHl034qft6wpY4eDcsTt5AaioBiU=
 golang.org/x/tools v0.1.9/go.mod h1:nABZi5QlRsZVlzPpHl034qft6wpY4eDcsTt5AaioBiU=
 golang.org/x/tools v0.1.10/go.mod h1:Uh6Zz+xoGYZom868N8YTex3t7RhtHDBrE8Gzo9bV56E=
 golang.org/x/tools v0.1.11/go.mod h1:SgwaegtQh8clINPpECJMqnxLv9I09HLqnW3RMqW0CA4=
@@ -1608,6 +1662,8 @@ golang.zx2c4.com/wireguard/windows v0.5.3 h1:On6j2Rpn3OEMXqBq00QEDC7bWSZrPIHKIus
 golang.zx2c4.com/wireguard/windows v0.5.3/go.mod h1:9TEe8TJmtwyQebdFwAkEWOPr3prrtqm+REGFifP60hI=
 gomodules.xyz/jsonpatch/v2 v2.4.0 h1:Ci3iUJyx9UeRx7CeFN8ARgGbkESwJK+KB9lLcWxY/Zw=
 gomodules.xyz/jsonpatch/v2 v2.4.0/go.mod h1:AH3dM2RI6uoBZxn3LVrfvJ3E0/9dG4cSrbuBJT4moAY=
+gonum.org/v1/gonum v0.16.0 h1:5+ul4Swaf3ESvrOnidPp4GZbzf0mxVQpDCYUQE7OJfk=
+gonum.org/v1/gonum v0.16.0/go.mod h1:fef3am4MQ93R2HHpKnLk4/Tbh/s0+wqD5nfa6Pnwy4E=
 google.golang.org/api v0.4.0/go.mod h1:8k5glujaEP+g9n7WNsDg8QP6cUVNI86fCNMcbazEtwE=
 google.golang.org/api v0.7.0/go.mod h1:WtwebWUNSVBH/HAw79HIFXZNqEvBhG+Ra+ax0hx3E3M=
 google.golang.org/api v0.8.0/go.mod h1:o4eAsZoiT+ibD93RtjEohWalFOjRDx6CVaqeizhEnKg=
@@ -1651,6 +1707,7 @@ google.golang.org/genproto v0.0.0-20200228133532-8c2c7df3a383/go.mod h1:55QSHmfG
 google.golang.org/genproto v0.0.0-20200305110556-506484158171/go.mod h1:55QSHmfGQM9UVYDPBsyGGes0y52j32PQ3BqQfXhyH3c=
 google.golang.org/genproto v0.0.0-20200312145019-da6875a35672/go.mod h1:55QSHmfGQM9UVYDPBsyGGes0y52j32PQ3BqQfXhyH3c=
 google.golang.org/genproto v0.0.0-20200331122359-1ee6d9798940/go.mod h1:55QSHmfGQM9UVYDPBsyGGes0y52j32PQ3BqQfXhyH3c=
+google.golang.org/genproto v0.0.0-20200423170343-7949de9c1215/go.mod h1:55QSHmfGQM9UVYDPBsyGGes0y52j32PQ3BqQfXhyH3c=
 google.golang.org/genproto v0.0.0-20200430143042-b979b6f78d84/go.mod h1:55QSHmfGQM9UVYDPBsyGGes0y52j32PQ3BqQfXhyH3c=
 google.golang.org/genproto v0.0.0-20200511104702-f5ebc3bea380/go.mod h1:55QSHmfGQM9UVYDPBsyGGes0y52j32PQ3BqQfXhyH3c=
 google.golang.org/genproto v0.0.0-20200515170657-fc4c6c6a6587/go.mod h1:YsZOwe1myG/8QRHRsmBRE1LrgQY60beZKjly0O1fX9U=
@@ -1677,6 +1734,8 @@ google.golang.org/grpc v1.30.0/go.mod h1:N36X2cJ7JwdamYAgDz+s+rVMFjt3numwzf/HckM
 google.golang.org/grpc v1.31.0/go.mod h1:N36X2cJ7JwdamYAgDz+s+rVMFjt3numwzf/HckM8pak=
 google.golang.org/grpc v1.78.0 h1:K1XZG/yGDJnzMdd/uZHAkVqJE+xIDOcmdSFZkBUicNc=
 google.golang.org/grpc v1.78.0/go.mod h1:I47qjTo4OKbMkjA/aOOwxDIiPSBofUtQUI5EfpWvW7U=
+google.golang.org/grpc/examples v0.0.0-20240321213419-eb5828bae753 h1:crPucDOfTtZF6lBfOiv4ex+5g+TFoNjyiSrSDJUpYPc=
+google.golang.org/grpc/examples v0.0.0-20240321213419-eb5828bae753/go.mod h1:fYxPglWChrD7bqbWtDwno019ra5SPuE1c3i+4YAvado=
 google.golang.org/protobuf v0.0.0-20200109180630-ec00e32a8dfd/go.mod h1:DFci5gLYBciE7Vtevhsrf46CRTquxDuWsQurQQe4oz8=
 google.golang.org/protobuf v0.0.0-20200221191635-4d8936d0db64/go.mod h1:kwYJMbMJ01Woi6D6+Kah6886xMZcty6N08ah7+eCXa0=
 google.golang.org/protobuf v0.0.0-20200228230310-ab0ca4ff8a60/go.mod h1:cfTl7dwQJ+fmap5saPgwCLgHXTUD7jkjRqWcaiX5VyM=
@@ -1704,8 +1763,6 @@ gopkg.in/h2non/gock.v1 v1.1.2 h1:jBbHXgGBK/AoPVfJh5x4r/WxIrElvbLel8TCZkkZJoY=
 gopkg.in/h2non/gock.v1 v1.1.2/go.mod h1:n7UGz/ckNChHiK05rDoiC4MYSunEC/lyaUm2WWaDva0=
 gopkg.in/inf.v0 v0.9.1 h1:73M5CoZyi3ZLMOyDlQh031Cx6N9NDJ2Vvfl76EDAgDc=
 gopkg.in/inf.v0 v0.9.1/go.mod h1:cWUDdTG/fYaXco+Dcufb5Vnc6Gp2YChqWtbxRZE0mXw=
-gopkg.in/ini.v1 v1.67.0 h1:Dgnx+6+nfE+IfzjUEISNeydPJh9AXNNsWbGP9KzCsOA=
-gopkg.in/ini.v1 v1.67.0/go.mod h1:pNLf8WUiyNEtQjuu5G5vTm06TEv9tsIgeAvK8hOrP4k=
 gopkg.in/square/go-jose.v2 v2.6.0 h1:NGk74WTnPKBNUhNzQX7PYcTLUjoq7mzKk2OKbvwk2iI=
 gopkg.in/square/go-jose.v2 v2.6.0/go.mod h1:M9dMgbHiYLoDGQrXy7OpJDJWiKiU//h+vD76mk0e1AI=
 gopkg.in/tomb.v1 v1.0.0-20141024135613-dd632973f1e7 h1:uRGJdciOHaEIrze2W8Q3AKkepLTh2hOroT7a+7czfdQ=
@@ -1722,6 +1779,7 @@ gopkg.in/yaml.v2 v2.3.0/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=
 gopkg.in/yaml.v2 v2.4.0 h1:D8xgwECY7CYvx+Y2n4sBz93Jn9JRvxdiyyo8CTfuKaY=
 gopkg.in/yaml.v2 v2.4.0/go.mod h1:RDklbk79AGWmwhnvt/jBztapEOGDOx6ZbXqjP6csGnQ=
 gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
+gopkg.in/yaml.v3 v3.0.0-20210107192922-496545a6307b/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
 gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
 gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
 gotest.tools/v3 v3.4.0 h1:ZazjZUfuVeZGLAmlKKuyv3IKP5orXcwtOwDQH6YVr6o=
@@ -1763,6 +1821,32 @@ k8s.io/kubectl v0.34.0 h1:NcXz4TPTaUwhiX4LU+6r6udrlm0NsVnSkP3R9t0dmxs=
 k8s.io/kubectl v0.34.0/go.mod h1:bmd0W5i+HuG7/p5sqicr0Li0rR2iIhXL0oUyLF3OjR4=
 k8s.io/utils v0.0.0-20250604170112-4c0f3b243397 h1:hwvWFiBzdWw1FhfY1FooPn3kzWuJ8tmbZBHi4zVsl1Y=
 k8s.io/utils v0.0.0-20250604170112-4c0f3b243397/go.mod h1:OLgZIPagt7ERELqWJFomSt595RzquPNLL48iOWgYOg0=
+modernc.org/cc/v4 v4.26.2 h1:991HMkLjJzYBIfha6ECZdjrIYz2/1ayr+FL8GN+CNzM=
+modernc.org/cc/v4 v4.26.2/go.mod h1:uVtb5OGqUKpoLWhqwNQo/8LwvoiEBLvZXIQ/SmO6mL0=
+modernc.org/ccgo/v4 v4.28.0 h1:rjznn6WWehKq7dG4JtLRKxb52Ecv8OUGah8+Z/SfpNU=
+modernc.org/ccgo/v4 v4.28.0/go.mod h1:JygV3+9AV6SmPhDasu4JgquwU81XAKLd3OKTUDNOiKE=
+modernc.org/fileutil v1.3.8 h1:qtzNm7ED75pd1C7WgAGcK4edm4fvhtBsEiI/0NQ54YM=
+modernc.org/fileutil v1.3.8/go.mod h1:HxmghZSZVAz/LXcMNwZPA/DRrQZEVP9VX0V4LQGQFOc=
+modernc.org/gc/v2 v2.6.5 h1:nyqdV8q46KvTpZlsw66kWqwXRHdjIlJOhG6kxiV/9xI=
+modernc.org/gc/v2 v2.6.5/go.mod h1:YgIahr1ypgfe7chRuJi2gD7DBQiKSLMPgBQe9oIiito=
+modernc.org/goabi0 v0.2.0 h1:HvEowk7LxcPd0eq6mVOAEMai46V+i7Jrj13t4AzuNks=
+modernc.org/goabi0 v0.2.0/go.mod h1:CEFRnnJhKvWT1c1JTI3Avm+tgOWbkOu5oPA8eH8LnMI=
+modernc.org/libc v1.66.3 h1:cfCbjTUcdsKyyZZfEUKfoHcP3S0Wkvz3jgSzByEWVCQ=
+modernc.org/libc v1.66.3/go.mod h1:XD9zO8kt59cANKvHPXpx7yS2ELPheAey0vjIuZOhOU8=
+modernc.org/mathutil v1.7.1 h1:GCZVGXdaN8gTqB1Mf/usp1Y/hSqgI2vAGGP4jZMCxOU=
+modernc.org/mathutil v1.7.1/go.mod h1:4p5IwJITfppl0G4sUEDtCr4DthTaT47/N3aT6MhfgJg=
+modernc.org/memory v1.11.0 h1:o4QC8aMQzmcwCK3t3Ux/ZHmwFPzE6hf2Y5LbkRs+hbI=
+modernc.org/memory v1.11.0/go.mod h1:/JP4VbVC+K5sU2wZi9bHoq2MAkCnrt2r98UGeSK7Mjw=
+modernc.org/opt v0.1.4 h1:2kNGMRiUjrp4LcaPuLY2PzUfqM/w9N23quVwhKt5Qm8=
+modernc.org/opt v0.1.4/go.mod h1:03fq9lsNfvkYSfxrfUhZCWPk1lm4cq4N+Bh//bEtgns=
+modernc.org/sortutil v1.2.1 h1:+xyoGf15mM3NMlPDnFqrteY07klSFxLElE2PVuWIJ7w=
+modernc.org/sortutil v1.2.1/go.mod h1:7ZI3a3REbai7gzCLcotuw9AC4VZVpYMjDzETGsSMqJE=
+modernc.org/sqlite v1.39.0 h1:6bwu9Ooim0yVYA7IZn9demiQk/Ejp0BtTjBWFLymSeY=
+modernc.org/sqlite v1.39.0/go.mod h1:cPTJYSlgg3Sfg046yBShXENNtPrWrDX8bsbAQBzgQ5E=
+modernc.org/strutil v1.2.1 h1:UneZBkQA+DX2Rp35KcM69cSsNES9ly8mQWD71HKlOA0=
+modernc.org/strutil v1.2.1/go.mod h1:EHkiggD70koQxjVdSBM3JKM7k6L0FbGE5eymy9i3B9A=
+modernc.org/token v1.1.0 h1:Xl7Ap9dKaEs5kLoOQeQmPWevfnk/DM5qcLcYlA8ys6Y=
+modernc.org/token v1.1.0/go.mod h1:UGzOrNV1mAFSEB63lOFHIpNRUVMvYTc6yu1SMY/XTDM=
 mvdan.cc/gofumpt v0.6.0 h1:G3QvahNDmpD+Aek/bNOLrFR2XC6ZAdo62dZu65gmwGo=
 mvdan.cc/gofumpt v0.6.0/go.mod h1:4L0wf+kgIPZtcCWXynNS2e6bhmj73umwnuXSZarixzA=
 mvdan.cc/unparam v0.0.0-20240104100049-c549a3470d14 h1:zCr3iRRgdk5eIikZNDphGcM6KGVTx3Yu+/Uu9Es254w=
@@ -1792,3 +1876,5 @@ sigs.k8s.io/yaml v1.6.0 h1:G8fkbMSAFqgEFgh4b1wmtzDnioxFCUgTZhlbj5P9QYs=
 sigs.k8s.io/yaml v1.6.0/go.mod h1:796bPqUfzR/0jLAl6XjHl3Ck7MiyVv8dbTdyT3/pMf4=
 software.sslmate.com/src/go-pkcs12 v0.4.0 h1:H2g08FrTvSFKUj+D309j1DPfk5APnIdAQAB8aEykJ5k=
 software.sslmate.com/src/go-pkcs12 v0.4.0/go.mod h1:Qiz0EyvDRJjjxGyUQa2cCNZn/wMyzrRJ/qcDXOQazLI=
+zgo.at/zcache/v2 v2.1.0 h1:USo+ubK+R4vtjw4viGzTe/zjXyPw6R7SK/RL3epBBxs=
+zgo.at/zcache/v2 v2.1.0/go.mod h1:gyCeoLVo01QjDZynjime8xUGHHMbsLiPyUTBpDGd4Gk=
diff --git a/gokrazy/gokrazy_test.go b/gokrazy/gokrazy_test.go
new file mode 100644
index 0000000000000..76398d49bf594
--- /dev/null
+++ b/gokrazy/gokrazy_test.go
@@ -0,0 +1,286 @@
+// Copyright (c) Tailscale Inc & contributors
+// SPDX-License-Identifier: BSD-3-Clause
+
+package main
+
+import (
+	"encoding/json"
+	"flag"
+	"fmt"
+	"hash/fnv"
+	"io"
+	"net"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strings"
+	"sync"
+	"testing"
+	"time"
+
+	"golang.org/x/mod/modfile"
+)
+
+var runVMTests = flag.Bool("run-vm-tests", false, "run tests that require a VM")
+
+func findKernelPath(t *testing.T) string {
+	t.Helper()
+	goModPath := filepath.Join("..", "go.mod")
+	b, err := os.ReadFile(goModPath)
+	if err != nil {
+		t.Fatalf("reading go.mod: %v", err)
+	}
+	mf, err := modfile.Parse("go.mod", b, nil)
+	if err != nil {
+		t.Fatalf("parsing go.mod: %v", err)
+	}
+	goModB, err := exec.Command("go", "env", "GOMODCACHE").CombinedOutput()
+	if err != nil {
+		t.Fatalf("go env GOMODCACHE: %v", err)
+	}
+	for _, r := range mf.Require {
+		if r.Mod.Path == "github.com/tailscale/gokrazy-kernel" {
+			return strings.TrimSpace(string(goModB)) + "/" + r.Mod.String() + "/vmlinuz"
+		}
+	}
+	t.Fatal("failed to find gokrazy-kernel in go.mod")
+	return ""
+}
+
+// gptPartuuid returns the GPT PARTUUID for a gokrazy appliance partition,
+// matching the scheme used by monogok: fnv32a(hostname) formatted into
+// the gokrazy GUID prefix.
+func gptPartuuid(hostname string, partition uint16) string {
+	h := fnv.New32a()
+	h.Write([]byte(hostname))
+	return fmt.Sprintf("60c24cc1-f3f9-427a-8199-%08x00%02x", h.Sum32(), partition)
+}
+
+func buildTsappImage(t *testing.T) string {
+	t.Helper()
+	imgPath, err := filepath.Abs("tsapp.img")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if _, err := os.Stat(imgPath); err == nil {
+		t.Logf("using existing tsapp.img: %s", imgPath)
+		return imgPath
+	}
+
+	t.Logf("building tsapp.img...")
+	cmd := exec.Command("make", "image")
+	cmd.Dir, _ = os.Getwd()
+	cmd.Stdout = os.Stdout
+	cmd.Stderr = os.Stderr
+	if err := cmd.Run(); err != nil {
+		t.Fatalf("make image: %v", err)
+	}
+	if _, err := os.Stat(imgPath); err != nil {
+		t.Fatalf("tsapp.img not found after build: %v", err)
+	}
+	return imgPath
+}
+
+// serialLog collects serial console output in a thread-safe manner.
+type serialLog struct {
+	mu    sync.Mutex
+	lines []string
+}
+
+func (sl *serialLog) add(line string) {
+	sl.mu.Lock()
+	defer sl.mu.Unlock()
+	sl.lines = append(sl.lines, line)
+}
+
+func (sl *serialLog) lastN(n int) []string {
+	sl.mu.Lock()
+	defer sl.mu.Unlock()
+	if len(sl.lines) <= n {
+		cp := make([]string, len(sl.lines))
+		copy(cp, sl.lines)
+		return cp
+	}
+	cp := make([]string, n)
+	copy(cp, sl.lines[len(sl.lines)-n:])
+	return cp
+}
+
+func (sl *serialLog) findLine(pred func(string) bool) bool {
+	sl.mu.Lock()
+	defer sl.mu.Unlock()
+	for _, line := range sl.lines {
+		if pred(line) {
+			return true
+		}
+	}
+	return false
+}
+
+// TestBusyboxInTsapp boots the tsapp image in QEMU and verifies that
+// busybox is accessible via the serial console shell. This validates
+// that the serial-busybox package's extra files (the busybox binary)
+// are properly included in the image by monogok.
+func TestBusyboxInTsapp(t *testing.T) {
+	if !*runVMTests {
+		t.Skip("skipping VM test; set --run-vm-tests to run")
+	}
+
+	kernel := findKernelPath(t)
+	if _, err := os.Stat(kernel); err != nil {
+		t.Skipf("kernel not found at %s: %v", kernel, err)
+	}
+	t.Logf("kernel: %s", kernel)
+
+	// Read the hostname from config.json to compute the GPT PARTUUID.
+	cfgBytes, err := os.ReadFile("tsapp/config.json")
+	if err != nil {
+		t.Fatalf("reading tsapp/config.json: %v", err)
+	}
+	var cfg struct {
+		Hostname string
+	}
+	if err := json.Unmarshal(cfgBytes, &cfg); err != nil {
+		t.Fatalf("parsing config.json: %v", err)
+	}
+	rootParam := fmt.Sprintf("root=PARTUUID=%s/PARTNROFF=1", gptPartuuid(cfg.Hostname, 1))
+	t.Logf("root param: %s", rootParam)
+
+	imgPath := buildTsappImage(t)
+
+	// Create a temporary qcow2 overlay so we don't modify the original image.
+	tmpDir := t.TempDir()
+	disk := filepath.Join(tmpDir, "tsapp-test.qcow2")
+	out, err := exec.Command("qemu-img", "create",
+		"-f", "qcow2",
+		"-F", "raw",
+		"-b", imgPath,
+		disk).CombinedOutput()
+	if err != nil {
+		t.Fatalf("qemu-img create: %v, %s", err, out)
+	}
+
+	// Set up a Unix socket for the serial console.
+	sockPath := filepath.Join(tmpDir, "serial.sock")
+	ln, err := net.Listen("unix", sockPath)
+	if err != nil {
+		t.Fatalf("listen: %v", err)
+	}
+	defer ln.Close()
+
+	// Boot QEMU with microvm, explicit kernel, and serial via virtconsole
+	// connected to our Unix socket. The kernel sees hvc0 as the console
+	// device, and gokrazy uses it for the serial shell.
+	cmd := exec.Command("qemu-system-x86_64",
+		"-M", "microvm,isa-serial=off",
+		"-m", "1G",
+		"-nodefaults", "-no-user-config", "-nographic",
+		"-kernel", kernel,
+		"-append", "console=hvc0 "+rootParam+" ro init=/gokrazy/init panic=10 oops=panic pci=off nousb tsc=unstable clocksource=hpet",
+		"-drive", "id=blk0,file="+disk+",format=qcow2",
+		"-device", "virtio-blk-device,drive=blk0",
+		"-device", "virtio-rng-device",
+		"-device", "virtio-serial-device",
+		"-chardev", "socket,id=virtiocon0,path="+sockPath+",server=off",
+		"-device", "virtconsole,chardev=virtiocon0",
+		"-netdev", "user,id=net0",
+		"-device", "virtio-net-device,netdev=net0",
+	)
+	cmd.Stderr = os.Stderr
+	if err := cmd.Start(); err != nil {
+		t.Fatalf("qemu start: %v", err)
+	}
+	t.Cleanup(func() {
+		cmd.Process.Kill()
+		cmd.Wait()
+	})
+
+	// Accept the serial console connection from QEMU.
+	ln.(*net.UnixListener).SetDeadline(time.Now().Add(30 * time.Second))
+	conn, err := ln.Accept()
+	if err != nil {
+		t.Fatalf("accept serial connection: %v", err)
+	}
+	defer conn.Close()
+
+	// Read serial output in a goroutine.
+	slog := &serialLog{}
+	bootDone := make(chan struct{})
+	go func() {
+		buf := make([]byte, 4096)
+		var partial string
+		for {
+			n, err := conn.Read(buf)
+			if n > 0 {
+				partial += string(buf[:n])
+				for {
+					idx := strings.IndexByte(partial, '\n')
+					if idx < 0 {
+						break
+					}
+					line := strings.TrimRight(partial[:idx], "\r")
+					partial = partial[idx+1:]
+					slog.add(line)
+					t.Logf("serial: %s", line)
+					// gokrazy logs socket listener info when boot is done.
+					if strings.Contains(line, "listening on") {
+						select {
+						case <-bootDone:
+						default:
+							close(bootDone)
+						}
+					}
+				}
+			}
+			if err != nil {
+				if err != io.EOF {
+					t.Logf("serial read error: %v", err)
+				}
+				return
+			}
+		}
+	}()
+
+	// Wait for boot to complete (up to 120 seconds).
+	select {
+	case <-bootDone:
+		t.Logf("boot complete")
+	case <-time.After(120 * time.Second):
+		t.Fatalf("timeout waiting for boot; last lines:\n%s",
+			strings.Join(slog.lastN(20), "\n"))
+	}
+
+	// Small delay to let services fully initialize.
+	time.Sleep(2 * time.Second)
+
+	// Send a newline to trigger the serial shell.
+	// gokrazy's init reads stdin and calls tryStartShell() on any input.
+	fmt.Fprintf(conn, "\n")
+	time.Sleep(2 * time.Second)
+
+	// Send a command to test busybox. The echo command is a busybox builtin,
+	// so if busybox is working, we'll see our marker in the output.
+	marker := "BUSYBOX_TEST_OK_12345"
+	fmt.Fprintf(conn, "echo %s\n", marker)
+
+	// Wait for our marker in the output (not on the echo command line itself).
+	deadline := time.After(15 * time.Second)
+	for {
+		select {
+		case <-deadline:
+			t.Fatalf("timeout waiting for busybox echo response; busybox binary is likely missing from the image.\n"+
+				"This indicates monogok is not copying _gokrazy/extrafiles from serial-busybox.\n"+
+				"Last serial lines:\n%s",
+				strings.Join(slog.lastN(30), "\n"))
+		default:
+		}
+		time.Sleep(200 * time.Millisecond)
+		// Look for the marker on a line by itself (the echo output, not the command).
+		if slog.findLine(func(line string) bool {
+			return strings.TrimSpace(line) == marker
+		}) {
+			t.Logf("busybox shell is working: got echo response")
+			return // success
+		}
+	}
+}
diff --git a/ipn/ipnlocal/local.go b/ipn/ipnlocal/local.go
index ea5af0897a54a..c7da0d3cbe066 100644
--- a/ipn/ipnlocal/local.go
+++ b/ipn/ipnlocal/local.go
@@ -4888,6 +4888,23 @@ func (b *LocalBackend) hostInfoWithServicesLocked() *tailcfg.Hostinfo {
 	// the slice with no free capacity.
 	c := len(hi.Services)
 	hi.Services = append(hi.Services[:c:c], peerAPIServices...)
+
+	// Advertise SCION service if available. Since the coord server only
+	// relays peerapi4/peerapi6 services to peers, we encode the SCION info
+	// directly into the peerapi4 service's Description field so it reaches
+	// peers without coord server changes.
+	if scionSvc, ok := b.MagicConn().SCIONService(); ok {
+		// Still include the standalone SCION service for the coord server.
+		hi.Services = append(hi.Services, scionSvc)
+		// Also piggyback on peerapi4's Description field.
+		for i := range hi.Services {
+			if hi.Services[i].Proto == tailcfg.PeerAPI4 {
+				hi.Services[i].Description = fmt.Sprintf("scion=%s:%d", scionSvc.Description, scionSvc.Port)
+				break
+			}
+		}
+	}
+
 	hi.PushDeviceToken = b.pushDeviceToken.Load()
 
 	// Compare the expected ports from peerAPIServices to the actual ports in hi.Services.
@@ -6299,6 +6316,9 @@ func (b *LocalBackend) setNetMapLocked(nm *netmap.NetworkMap) {
 
 	// See the netns package for documentation on what these capability do.
 	netns.SetBindToInterfaceByRoute(b.logf, nm.HasCap(tailcfg.CapabilityBindToInterfaceByRoute))
+	if runtime.GOOS == "android" {
+		netns.SetDisableAndroidBindToActiveNetwork(b.logf, nm.HasCap(tailcfg.NodeAttrDisableAndroidBindToActiveNetwork))
+	}
 	netns.SetDisableBindConnToInterface(b.logf, nm.HasCap(tailcfg.CapabilityDebugDisableBindConnToInterface))
 	netns.SetDisableBindConnToInterfaceAppleExt(b.logf, nm.HasCap(tailcfg.CapabilityDebugDisableBindConnToInterfaceAppleExt))
 
diff --git a/ipn/ipnstate/ipnstate.go b/ipn/ipnstate/ipnstate.go
index 17e6ac870bead..f0eb82eb14814 100644
--- a/ipn/ipnstate/ipnstate.go
+++ b/ipn/ipnstate/ipnstate.go
@@ -176,6 +176,16 @@ type TailnetStatus struct {
 	MagicDNSEnabled bool
 }
 
+// SCIONPathInfo describes a SCION path to a peer.
+type SCIONPathInfo struct {
+	Path      string  `json:"Path"`
+	Active    bool    `json:"Active"`
+	Healthy   bool    `json:"Healthy"`
+	LatencyMs float64 `json:"LatencyMs"`
+	ExpiresAt string  `json:"ExpiresAt,omitempty"`
+	MTU       int     `json:"MTU,omitempty"`
+}
+
 // ExitNodeStatus describes the current exit node.
 type ExitNodeStatus struct {
 	// ID is the exit node's ID.
@@ -256,6 +266,8 @@ type PeerStatus struct {
 	Relay     string // DERP region
 	PeerRelay string // peer relay address (ip:port:vni)
 
+	SCIONPaths []SCIONPathInfo `json:"SCIONPaths,omitempty"`
+
 	RxBytes        int64
 	TxBytes        int64
 	Created        time.Time // time registered with tailcontrol
@@ -545,6 +557,9 @@ func (sb *StatusBuilder) AddPeer(peer key.NodePublic, st *PeerStatus) {
 	if v := st.TaildropTarget; v != TaildropTargetUnknown {
 		e.TaildropTarget = v
 	}
+	if v := st.SCIONPaths; v != nil {
+		e.SCIONPaths = v
+	}
 	e.Location = st.Location
 }
 
diff --git a/ipn/localapi/localapi_scion.go b/ipn/localapi/localapi_scion.go
new file mode 100644
index 0000000000000..cbb24ca6e697f
--- /dev/null
+++ b/ipn/localapi/localapi_scion.go
@@ -0,0 +1,40 @@
+// Copyright (c) Tailscale Inc & contributors
+// Copyright (c) 2026 netsys-lab
+// SPDX-License-Identifier: BSD-3-Clause
+
+//go:build !ts_omit_scion
+
+package localapi
+
+import (
+	"encoding/json"
+	"net/http"
+)
+
+func init() {
+	Register("scion-status", (*Handler).serveSCIONStatus)
+}
+
+// SCIONStatusResponse is the JSON response for GET /localapi/v0/scion-status.
+type SCIONStatusResponse struct {
+	Connected bool   `json:"Connected"`
+	LocalIA   string `json:"LocalIA,omitempty"`
+}
+
+func (h *Handler) serveSCIONStatus(w http.ResponseWriter, r *http.Request) {
+	if r.Method != "GET" {
+		http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
+		return
+	}
+	mc := h.b.MagicConn()
+	if mc == nil {
+		http.Error(w, "not ready", http.StatusServiceUnavailable)
+		return
+	}
+	connected, localIA := mc.SCIONStatus()
+	w.Header().Set("Content-Type", "application/json")
+	json.NewEncoder(w).Encode(SCIONStatusResponse{
+		Connected: connected,
+		LocalIA:   localIA,
+	})
+}
\ No newline at end of file
diff --git a/ipn/localapi/localapi_scion_omit.go b/ipn/localapi/localapi_scion_omit.go
new file mode 100644
index 0000000000000..e2d4ac1ee0b6c
--- /dev/null
+++ b/ipn/localapi/localapi_scion_omit.go
@@ -0,0 +1,7 @@
+// Copyright (c) Tailscale Inc & contributors
+// Copyright (c) 2026 netsys-lab
+// SPDX-License-Identifier: BSD-3-Clause
+
+//go:build ts_omit_scion
+
+package localapi
\ No newline at end of file
diff --git a/kube/kubetypes/types.go b/kube/kubetypes/types.go
index 187f54f3481f8..9f1b29064acca 100644
--- a/kube/kubetypes/types.go
+++ b/kube/kubetypes/types.go
@@ -38,17 +38,17 @@ const (
 	// Keys that containerboot writes to state file that can be used to determine its state.
 	// fields set in Tailscale state Secret. These are mostly used by the Tailscale Kubernetes operator to determine
 	// the state of this tailscale device.
-	KeyDeviceID   string = "device_id"   // node stable ID of the device
-	KeyDeviceFQDN string = "device_fqdn" // device's tailnet hostname
-	KeyDeviceIPs  string = "device_ips"  // device's tailnet IPs
-	KeyPodUID     string = "pod_uid"     // Pod UID
-	// KeyCapVer contains Tailscale capability version of this proxy instance.
-	KeyCapVer string = "tailscale_capver"
+	KeyDeviceID       = "device_id"        // node stable ID of the device
+	KeyDeviceFQDN     = "device_fqdn"      // device's tailnet hostname
+	KeyDeviceIPs      = "device_ips"       // device's tailnet IPs
+	KeyPodUID         = "pod_uid"          // Pod UID
+	KeyCapVer         = "tailscale_capver" // tailcfg.CurrentCapabilityVersion of this proxy instance.
+	KeyReissueAuthkey = "reissue_authkey"  // Proxies will set this to the authkey that failed, or "no-authkey", if they can't log in.
 	// KeyHTTPSEndpoint is a name of a field that can be set to the value of any HTTPS endpoint currently exposed by
 	// this device to the tailnet. This is used by the Kubernetes operator Ingress proxy to communicate to the operator
 	// that cluster workloads behind the Ingress can now be accessed via the given DNS name over HTTPS.
-	KeyHTTPSEndpoint string = "https_endpoint"
-	ValueNoHTTPS     string = "no-https"
+	KeyHTTPSEndpoint = "https_endpoint"
+	ValueNoHTTPS     = "no-https"
 
 	// Pod's IPv4 address header key as returned by containerboot health check endpoint.
 	PodIPv4Header string = "Pod-IPv4"
diff --git a/net/batching/conn.go b/net/batching/conn.go
index 1631c33cfe448..1843a2cfced5a 100644
--- a/net/batching/conn.go
+++ b/net/batching/conn.go
@@ -19,14 +19,24 @@ var (
 	_ ipv6.Message = ipv4.Message{}
 )
 
-// Conn is a nettype.PacketConn that provides batched i/o using
+// Conn is a [nettype.PacketConn] that provides batched i/o using
 // platform-specific optimizations, e.g. {recv,send}mmsg & UDP GSO/GRO.
 //
+// Conn does not support single packet reads (see ReadFromUDPAddrPort docs). It
+// is the caller's responsibility to use the appropriate read API where a
+// [nettype.PacketConn] has been upgraded to support batched i/o.
+//
 // Conn originated from (and is still used by) magicsock where its API was
 // strongly influenced by [wireguard-go/conn.Bind] constraints, namely
 // wireguard-go's ownership of packet memory.
 type Conn interface {
 	nettype.PacketConn
+	// ReadFromUDPAddrPort always returns an error, as UDP GRO is incompatible
+	// with single packet reads. A single datagram may be multiple, coalesced
+	// datagrams, and this API lacks the ability to pass that context.
+	//
+	// TODO: consider detaching Conn from [nettype.PacketConn]
+	ReadFromUDPAddrPort([]byte) (int, netip.AddrPort, error)
 	// ReadBatch reads messages from [Conn] into msgs. It returns the number of
 	// messages the caller should evaluate for nonzero len, as a zero len
 	// message may fall on either side of a nonzero.
diff --git a/net/batching/conn_linux.go b/net/batching/conn_linux.go
index 373625b772738..70f91cfb6847c 100644
--- a/net/batching/conn_linux.go
+++ b/net/batching/conn_linux.go
@@ -61,16 +61,7 @@ type linuxBatchingConn struct {
 }
 
 func (c *linuxBatchingConn) ReadFromUDPAddrPort(p []byte) (n int, addr netip.AddrPort, err error) {
-	if c.rxOffload {
-		// UDP_GRO is opt-in on Linux via setsockopt(). Once enabled you may
-		// receive a "monster datagram" from any read call. The ReadFrom() API
-		// does not support passing the GSO size and is unsafe to use in such a
-		// case. Other platforms may vary in behavior, but we go with the most
-		// conservative approach to prevent this from becoming a footgun in the
-		// future.
-		return 0, netip.AddrPort{}, errors.New("rx UDP offload is enabled on this socket, single packet reads are unavailable")
-	}
-	return c.pc.ReadFromUDPAddrPort(p)
+	return 0, netip.AddrPort{}, errors.New("single packet reads are unsupported")
 }
 
 func (c *linuxBatchingConn) SetDeadline(t time.Time) error {
diff --git a/net/netns/netns.go b/net/netns/netns.go
index 5d692c787eae8..fe7ff4dcbadd8 100644
--- a/net/netns/netns.go
+++ b/net/netns/netns.go
@@ -46,6 +46,18 @@ func SetBindToInterfaceByRoute(logf logger.Logf, v bool) {
 	}
 }
 
+// When true, disableAndroidBindToActiveNetwork skips binding sockets to the currently
+// active network on Android.
+var disableAndroidBindToActiveNetwork atomic.Bool
+
+// SetDisableAndroidBindToActiveNetwork disables the default behavior of binding
+// sockets to the currently active network on Android.
+func SetDisableAndroidBindToActiveNetwork(logf logger.Logf, v bool) {
+	if runtime.GOOS == "android" && disableAndroidBindToActiveNetwork.Swap(v) != v {
+		logf("netns: disableAndroidBindToActiveNetwork changed to %v", v)
+	}
+}
+
 var disableBindConnToInterface atomic.Bool
 
 // SetDisableBindConnToInterface disables the (normal) behavior of binding
diff --git a/net/netns/netns_android.go b/net/netns/netns_android.go
index e747f61f40e50..7c5fe3214dcbf 100644
--- a/net/netns/netns_android.go
+++ b/net/netns/netns_android.go
@@ -17,6 +17,9 @@ import (
 var (
 	androidProtectFuncMu sync.Mutex
 	androidProtectFunc   func(fd int) error
+
+	androidBindToNetworkFuncMu sync.Mutex
+	androidBindToNetworkFunc   func(fd int) error
 )
 
 // UseSocketMark reports whether SO_MARK is in use. Android does not use SO_MARK.
@@ -50,6 +53,14 @@ func SetAndroidProtectFunc(f func(fd int) error) {
 	androidProtectFunc = f
 }
 
+// SetAndroidBindToNetworkFunc registers a func provided by Android that binds
+// the socket FD to the currently selected underlying network.
+func SetAndroidBindToNetworkFunc(f func(fd int) error) {
+	androidBindToNetworkFuncMu.Lock()
+	defer androidBindToNetworkFuncMu.Unlock()
+	androidBindToNetworkFunc = f
+}
+
 func control(logger.Logf, *netmon.Monitor) func(network, address string, c syscall.RawConn) error {
 	return controlC
 }
@@ -60,14 +71,36 @@ func control(logger.Logf, *netmon.Monitor) func(network, address string, c sysca
 // and net.ListenConfig.Control.
 func controlC(network, address string, c syscall.RawConn) error {
 	var sockErr error
+
 	err := c.Control(func(fd uintptr) {
+		fdInt := int(fd)
+
+		// Protect from VPN loops
 		androidProtectFuncMu.Lock()
-		f := androidProtectFunc
+		pf := androidProtectFunc
 		androidProtectFuncMu.Unlock()
-		if f != nil {
-			sockErr = f(int(fd))
+		if pf != nil {
+			if err := pf(fdInt); err != nil {
+				sockErr = err
+				return
+			}
+		}
+
+		if disableAndroidBindToActiveNetwork.Load() {
+			return
+		}
+
+		androidBindToNetworkFuncMu.Lock()
+		bf := androidBindToNetworkFunc
+		androidBindToNetworkFuncMu.Unlock()
+		if bf != nil {
+			if err := bf(fdInt); err != nil {
+				sockErr = err
+				return
+			}
 		}
 	})
+
 	if err != nil {
 		return fmt.Errorf("RawConn.Control on %T: %w", c, err)
 	}
diff --git a/release/dist/dist.go b/release/dist/dist.go
index 094d0a0e04c46..46646c876e0ec 100644
--- a/release/dist/dist.go
+++ b/release/dist/dist.go
@@ -324,7 +324,10 @@ func (b *Build) Command(dir, cmd string, args ...string) *Command {
 		ret.Cmd.Stderr = &ret.Output
 	}
 	// dist always wants to use gocross if any Go is involved.
-	ret.Cmd.Env = append(os.Environ(), "TS_USE_GOCROSS=1")
+	// Suppress bash debug traces (set -x) from tool/go in CI, because
+	// GoPkg() uses CombinedOutput() and set -x pollutes stdout+stderr,
+	// causing "no matching files" errors when building deb/rpm packages.
+	ret.Cmd.Env = append(os.Environ(), "TS_USE_GOCROSS=1", "NOBASHDEBUG=true")
 	ret.Cmd.Dir = dir
 	return ret
 }
diff --git a/release/dist/unixpkgs/pkgs.go b/release/dist/unixpkgs/pkgs.go
index d251ff621f98a..fe9df18cf2bae 100644
--- a/release/dist/unixpkgs/pkgs.go
+++ b/release/dist/unixpkgs/pkgs.go
@@ -46,7 +46,7 @@ func (t *tgzTarget) Build(b *dist.Build) ([]string, error) {
 	if t.goEnv["GOOS"] == "linux" {
 		// Linux used to be the only tgz architecture, so we didn't put the OS
 		// name in the filename.
-		filename = fmt.Sprintf("tailscale_%s_%s.tgz", b.Version.Short, t.arch())
+		filename = fmt.Sprintf("tailscale-scion_%s_%s.tgz", b.Version.Short, t.arch())
 	} else {
 		filename = fmt.Sprintf("tailscale_%s_%s_%s.tgz", b.Version.Short, t.os(), t.arch())
 	}
@@ -233,14 +233,14 @@ func (t *debTarget) Build(b *dist.Build) ([]string, error) {
 		return nil, err
 	}
 	info := nfpm.WithDefaults(&nfpm.Info{
-		Name:        "tailscale",
+		Name:        "tailscale-scion",
 		Arch:        arch,
 		Platform:    "linux",
 		Version:     b.Version.Short,
-		Maintainer:  "Tailscale Inc <info@tailscale.com>",
-		Description: "The easiest, most secure, cross platform way to use WireGuard + oauth2 + 2FA/SSO",
-		Homepage:    "https://www.tailscale.com",
-		License:     "MIT",
+		Maintainer:  "netsys-lab",
+		Description: "Tailscale with SCION path-aware networking support",
+		Homepage:    "https://github.com/netsys-lab/tailscale-scion",
+		License:     "BSD-3-Clause",
 		Section:     "net",
 		Priority:    "extra",
 		Overridables: nfpm.Overridables{
@@ -251,20 +251,9 @@ func (t *debTarget) Build(b *dist.Build) ([]string, error) {
 				PostRemove:  filepath.Join(repoDir, "release/deb/debian.postrm.sh"),
 			},
 			Depends: []string{
-				// iptables is almost always required but not strictly needed.
-				// Even if you can technically run Tailscale without it (by
-				// manually configuring nftables or userspace mode), we still
-				// mark this as "Depends" because our previous experiment in
-				// https://github.com/tailscale/tailscale/issues/9236 of making
-				// it only Recommends caused too many problems. Until our
-				// nftables table is more mature, we'd rather err on the side of
-				// wasting a little disk by including iptables for people who
-				// might not need it rather than handle reports of it being
-				// missing.
 				"iptables",
 			},
 			Recommends: []string{
-				"tailscale-archive-keyring (>= 1.35.181)",
 				// The "ip" command isn't needed since 2021-11-01 in
 				// 408b0923a61972ed but kept as an option as of
 				// 2021-11-18 in d24ed3f68e35e802d531371.  See
@@ -274,8 +263,8 @@ func (t *debTarget) Build(b *dist.Build) ([]string, error) {
 				// we can live without it, so it's not Depends.
 				"iproute2",
 			},
-			Replaces:  []string{"tailscale-relay"},
-			Conflicts: []string{"tailscale-relay"},
+			Replaces:  []string{"tailscale", "tailscale-relay"},
+			Conflicts: []string{"tailscale", "tailscale-relay"},
 		},
 	})
 	pkg, err := nfpm.Get("deb")
@@ -283,7 +272,7 @@ func (t *debTarget) Build(b *dist.Build) ([]string, error) {
 		return nil, err
 	}
 
-	filename := fmt.Sprintf("tailscale_%s_%s.deb", b.Version.Short, arch)
+	filename := fmt.Sprintf("tailscale-scion_%s_%s.deb", b.Version.Short, arch)
 	log.Printf("Building %s", filename)
 	f, err := os.Create(filepath.Join(b.Out, filename))
 	if err != nil {
@@ -376,14 +365,14 @@ func (t *rpmTarget) Build(b *dist.Build) ([]string, error) {
 		return nil, err
 	}
 	info := nfpm.WithDefaults(&nfpm.Info{
-		Name:        "tailscale",
+		Name:        "tailscale-scion",
 		Arch:        arch,
 		Platform:    "linux",
 		Version:     b.Version.Short,
-		Maintainer:  "Tailscale Inc <info@tailscale.com>",
-		Description: "The easiest, most secure, cross platform way to use WireGuard + oauth2 + 2FA/SSO",
-		Homepage:    "https://www.tailscale.com",
-		License:     "MIT",
+		Maintainer:  "netsys-lab",
+		Description: "Tailscale with SCION path-aware networking support",
+		Homepage:    "https://github.com/netsys-lab/tailscale-scion",
+		License:     "BSD-3-Clause",
 		Overridables: nfpm.Overridables{
 			Contents: contents,
 			Scripts: nfpm.Scripts{
@@ -392,8 +381,8 @@ func (t *rpmTarget) Build(b *dist.Build) ([]string, error) {
 				PostRemove:  filepath.Join(repoDir, "release/rpm/rpm.postrm.sh"),
 			},
 			Depends:   []string{"iptables", "iproute"},
-			Replaces:  []string{"tailscale-relay"},
-			Conflicts: []string{"tailscale-relay"},
+			Replaces:  []string{"tailscale", "tailscale-relay"},
+			Conflicts: []string{"tailscale", "tailscale-relay"},
 			RPM: nfpm.RPM{
 				Group: "Network",
 				Signature: nfpm.RPMSignature{
@@ -409,7 +398,7 @@ func (t *rpmTarget) Build(b *dist.Build) ([]string, error) {
 		return nil, err
 	}
 
-	filename := fmt.Sprintf("tailscale_%s_%s.rpm", b.Version.Short, arch)
+	filename := fmt.Sprintf("tailscale-scion_%s_%s.rpm", b.Version.Short, arch)
 	log.Printf("Building %s", filename)
 
 	f, err := os.Create(filepath.Join(b.Out, filename))
diff --git a/shell.nix b/shell.nix
index 7e965bb11082a..17ad795876a58 100644
--- a/shell.nix
+++ b/shell.nix
@@ -16,4 +16,4 @@
 ) {
   src =  ./.;
 }).shellNix
-# nix-direnv cache busting line: sha256-dx+SJyDx+eZptFaMatoyM6w1E3nJKY+hKs7nuR997bE=
+# nix-direnv cache busting line: sha256-V4vJ1MonIWbuL+R5fUiO7hV7f+k/Iqoz+EFWnOJwZAs=
diff --git a/tailcfg/tailcfg.go b/tailcfg/tailcfg.go
index 1efa6c959214e..95af5525311d8 100644
--- a/tailcfg/tailcfg.go
+++ b/tailcfg/tailcfg.go
@@ -180,7 +180,8 @@ type CapabilityVersion int
 //   - 131: 2025-11-25: client respects [NodeAttrDefaultAutoUpdate]
 //   - 132: 2026-02-13: client respects [NodeAttrDisableHostsFileUpdates]
 //   - 133: 2026-02-17: client understands [NodeAttrForceRegisterMagicDNSIPv4Only]; MagicDNS IPv6 registered w/ OS by default
-const CurrentCapabilityVersion CapabilityVersion = 133
+//   - 134: 2026-03-09: Client understands [NodeAttrDisableAndroidBindToActiveNetwork]
+const CurrentCapabilityVersion CapabilityVersion = 134
 
 // ID is an integer ID for a user, node, or login allocated by the
 // control plane.
@@ -759,13 +760,14 @@ const (
 	PeerAPI4   = ServiceProto("peerapi4")
 	PeerAPI6   = ServiceProto("peerapi6")
 	PeerAPIDNS = ServiceProto("peerapi-dns-proxy")
+	SCION      = ServiceProto("scion")
 )
 
 // IsKnownServiceProto checks whether sp represents a known-valid value of
 // ServiceProto.
 func IsKnownServiceProto(sp ServiceProto) bool {
 	switch sp {
-	case TCP, UDP, PeerAPI4, PeerAPI6, PeerAPIDNS, ServiceProto("egg"):
+	case TCP, UDP, PeerAPI4, PeerAPI6, PeerAPIDNS, SCION, ServiceProto("egg"):
 		return true
 	}
 	return false
@@ -2463,6 +2465,12 @@ const (
 	// details on the behaviour of this capability.
 	CapabilityBindToInterfaceByRoute NodeCapability = "https://tailscale.com/cap/bind-to-interface-by-route"
 
+	// NodeAttrDisableAndroidBindToActiveNetwork disables binding sockets to the
+	// currently active network on Android, which is enabled by default.
+	// This allows the control plane to turn off the behavior if it causes
+	// problems.
+	NodeAttrDisableAndroidBindToActiveNetwork NodeCapability = "disable-android-bind-to-active-network"
+
 	// CapabilityDebugDisableAlternateDefaultRouteInterface changes how Darwin
 	// nodes get the default interface. There is an optional hook (used by the
 	// macOS and iOS clients) to override the default interface, this capability
@@ -2763,6 +2771,12 @@ const (
 	// See https://github.com/tailscale/tailscale/issues/15404.
 	// TODO(bradfitz): remove this a few releases after 2026-02-16.
 	NodeAttrForceRegisterMagicDNSIPv4Only NodeCapability = "force-register-magicdns-ipv4-only"
+
+	// NodeAttrSCIONPrefer indicates that the node should prefer SCION paths
+	// when communicating with other SCION-capable peers that also have this
+	// attribute. Both self and peer must have this attribute for SCION to be
+	// preferred over direct UDP.
+	NodeAttrSCIONPrefer NodeCapability = "scion-prefer"
 )
 
 // SetDNSRequest is a request to add a DNS record.
diff --git a/tsnet/tsnet.go b/tsnet/tsnet.go
index 4a116cf3467f7..38ea865998d14 100644
--- a/tsnet/tsnet.go
+++ b/tsnet/tsnet.go
@@ -151,6 +151,8 @@ type Server struct {
 
 	// ControlURL optionally specifies the coordination server URL.
 	// If empty, the Tailscale default is used.
+	// If empty, it defaults to the TS_CONTROL_URL environment variable.
+	// If that is also empty, the Tailscale default is used.
 	ControlURL string
 
 	// RunWebClient, if true, runs a client for managing this node over
@@ -568,6 +570,13 @@ func (s *Server) getAuthKey() string {
 	return os.Getenv("TS_AUTH_KEY")
 }
 
+func (s *Server) getControlURL() string {
+	if v := s.ControlURL; v != "" {
+		return v
+	}
+	return os.Getenv("TS_CONTROL_URL")
+}
+
 func (s *Server) getClientSecret() string {
 	if v := s.ClientSecret; v != "" {
 		return v
@@ -769,7 +778,7 @@ func (s *Server) start() (reterr error) {
 	prefs := ipn.NewPrefs()
 	prefs.Hostname = s.hostname
 	prefs.WantRunning = true
-	prefs.ControlURL = s.ControlURL
+	prefs.ControlURL = s.getControlURL()
 	prefs.RunWebClient = s.RunWebClient
 	prefs.AdvertiseTags = s.AdvertiseTags
 	authKey, err := s.resolveAuthKey()
@@ -858,7 +867,7 @@ func (s *Server) resolveAuthKey() (string, error) {
 				return "", fmt.Errorf("audience for workload identity federation found, but client ID is empty")
 			}
 		}
-		authKey, err = resolveViaWIF(s.shutdownCtx, s.ControlURL, clientID, idToken, audience, s.AdvertiseTags)
+		authKey, err = resolveViaWIF(s.shutdownCtx, s.getControlURL(), clientID, idToken, audience, s.AdvertiseTags)
 		if err != nil {
 			return "", err
 		}
diff --git a/wgengine/magicsock/derp.go b/wgengine/magicsock/derp.go
index f9e5050705b31..17e3cfa82ebe6 100644
--- a/wgengine/magicsock/derp.go
+++ b/wgengine/magicsock/derp.go
@@ -725,6 +725,10 @@ func (c *Conn) processDERPReadResult(dm derpReadResult, b []byte) (n int, ep *en
 		return 0, nil
 	}
 
+	if c.onDERPRecv != nil && c.onDERPRecv(regionID, dm.src, b[:n]) {
+		return 0, nil
+	}
+
 	var ok bool
 	c.mu.Lock()
 	ep, ok = c.peerMap.endpointForNodeKey(dm.src)
@@ -745,6 +749,15 @@ func (c *Conn) processDERPReadResult(dm derpReadResult, b []byte) (n int, ep *en
 	return n, ep
 }
 
+// SendDERPPacketTo sends an arbitrary packet to the given node key via
+// the DERP relay for the given region. It creates the DERP connection
+// to the region if one doesn't already exist.
+func (c *Conn) SendDERPPacketTo(dstKey key.NodePublic, regionID int, pkt []byte) (sent bool, err error) {
+	return c.sendAddr(
+		netip.AddrPortFrom(tailcfg.DerpMagicIPAddr, uint16(regionID)),
+		dstKey, pkt, false, false)
+}
+
 // SetOnlyTCP443 set whether the magicsock connection is restricted
 // to only using TCP port 443 outbound. If true, no UDP is allowed,
 // no STUN checks are performend, etc.
diff --git a/wgengine/magicsock/endpoint.go b/wgengine/magicsock/endpoint.go
index 5f493027be945..d9f0498c33d1a 100644
--- a/wgengine/magicsock/endpoint.go
+++ b/wgengine/magicsock/endpoint.go
@@ -99,6 +99,9 @@ type endpoint struct {
 	expired         bool // whether the node has expired
 	isWireguardOnly bool // whether the endpoint is WireGuard only
 	relayCapable    bool // whether the node is capable of speaking via a [tailscale.com/net/udprelay.Server]
+
+	scionState     *scionEndpointState // nil if peer has no SCION address
+	scionPreferred bool                // true if both self and peer have NodeAttrSCIONPrefer
 }
 
 // udpRelayEndpointReady determines whether the given relay [addrQuality] should
@@ -124,7 +127,7 @@ func (de *endpoint) udpRelayEndpointReady(maybeBest addrQuality) {
 		//
 		// TODO(jwhited): add observability around !curBestAddrTrusted and sameRelayServer
 		// TODO(jwhited): collapse path change logging with endpoint.handlePongConnLocked()
-		de.c.logf("magicsock: disco: node %v %v now using %v mtu=%v", de.publicKey.ShortString(), de.discoShort(), maybeBest.epAddr, maybeBest.wireMTU)
+		de.c.logf("magicsock: disco: node %v %v now using %v mtu=%v", de.publicKey.ShortString(), de.discoShort(), de.scionAddrStr(maybeBest.epAddr), maybeBest.wireMTU)
 		de.setBestAddrLocked(maybeBest)
 		de.trustBestAddrUntil = now.Add(trustUDPAddrDuration)
 	}
@@ -516,7 +519,8 @@ func (de *endpoint) noteRecvActivity(src epAddr, now mono.Time) bool {
 		// kick off discovery disco pings every trustUDPAddrDuration and mirror
 		// to DERP.
 		de.mu.Lock()
-		if de.heartbeatDisabled && de.bestAddr.epAddr == src {
+		if de.heartbeatDisabled && (de.bestAddr.epAddr == src ||
+			(de.bestAddr.isSCION() && de.bestAddr.ap == src.ap)) {
 			de.trustBestAddrUntil = now.Add(trustUDPAddrDuration)
 		}
 		de.mu.Unlock()
@@ -862,6 +866,8 @@ func (de *endpoint) heartbeat() {
 
 	if de.wantFullPingLocked(now) {
 		de.sendDiscoPingsLocked(now, true)
+	} else {
+		de.heartbeatSCIONLocked(now)
 	}
 
 	if de.wantUDPRelayPathDiscoveryLocked(now) {
@@ -933,7 +939,7 @@ func (de *endpoint) wantFullPingLocked(now mono.Time) bool {
 	if runtime.GOOS == "js" {
 		return false
 	}
-	if !de.bestAddr.isDirect() || de.lastFullPing.IsZero() {
+	if (!de.bestAddr.isDirect() && !de.bestAddr.isSCION()) || de.lastFullPing.IsZero() {
 		return true
 	}
 	if now.After(de.trustBestAddrUntil) {
@@ -1023,6 +1029,7 @@ func (de *endpoint) discoPing(res *ipnstate.PingResult, size int, cb func(*ipnst
 		for ep := range de.endpointState {
 			de.startDiscoPingLocked(epAddr{ap: ep}, now, pingCLI, size, resCB)
 		}
+		de.cliPingSCIONLocked(now, size, resCB)
 		if de.wantUDPRelayPathDiscoveryLocked(now) {
 			de.discoverUDPRelayPathsLocked(now)
 		}
@@ -1049,7 +1056,7 @@ func (de *endpoint) send(buffs [][]byte, offset int) error {
 		if startWGPing {
 			de.sendWireGuardOnlyPingsLocked(now)
 		}
-	} else if !udpAddr.isDirect() || now.After(de.trustBestAddrUntil) {
+	} else if (!udpAddr.isDirect() && !udpAddr.isSCION()) || now.After(de.trustBestAddrUntil) {
 		de.sendDiscoPingsLocked(now, true)
 		if de.wantUDPRelayPathDiscoveryLocked(now) {
 			de.discoverUDPRelayPathsLocked(now)
@@ -1071,7 +1078,9 @@ func (de *endpoint) send(buffs [][]byte, offset int) error {
 		}
 	}
 	var err error
-	if udpAddr.ap.IsValid() {
+	if udpAddr.isSCION() {
+		err = de.sendSCIONData(udpAddr, buffs, offset)
+	} else if udpAddr.ap.IsValid() {
 		_, err = de.c.sendUDPBatch(udpAddr, buffs, offset)
 
 		// If the error is known to indicate that the endpoint is no longer
@@ -1186,6 +1195,8 @@ func (de *endpoint) discoPingTimeout(txid stun.TxID) {
 		de.c.dlogf("[v1] magicsock: disco: timeout waiting for pong %x from %v (%v, %v)", txid[:6], sp.to, de.publicKey.ShortString(), de.discoShort())
 	}
 	de.removeSentDiscoPingLocked(txid, sp, discoPingTimedOut)
+
+	de.discoPingTimeoutSCIONLocked(sp)
 }
 
 // forgetDiscoPing is called when a ping fails to send.
@@ -1287,7 +1298,7 @@ func (de *endpoint) startDiscoPingLocked(ep epAddr, now mono.Time, purpose disco
 	if runtime.GOOS == "js" {
 		return
 	}
-	if debugNeverDirectUDP() && !ep.vni.IsSet() && ep.ap.Addr() != tailcfg.DerpMagicIPAddr {
+	if debugNeverDirectUDP() && !ep.vni.IsSet() && !ep.scionKey.IsSet() && ep.ap.Addr() != tailcfg.DerpMagicIPAddr {
 		return
 	}
 	epDisco := de.disco.Load()
@@ -1295,7 +1306,7 @@ func (de *endpoint) startDiscoPingLocked(ep epAddr, now mono.Time, purpose disco
 		return
 	}
 	if purpose != pingCLI &&
-		!ep.vni.IsSet() { // de.endpointState is only relevant for direct/non-vni epAddr's
+		!ep.vni.IsSet() && !ep.scionKey.IsSet() { // de.endpointState is only relevant for direct/non-vni/non-SCION epAddr's
 		st, ok := de.endpointState[ep.ap]
 		if !ok {
 			// Shouldn't happen. But don't ping an endpoint that's
@@ -1314,7 +1325,9 @@ func (de *endpoint) startDiscoPingLocked(ep epAddr, now mono.Time, purpose disco
 	sizes := []int{size}
 	if de.c.PeerMTUEnabled() {
 		isDerp := ep.ap.Addr() == tailcfg.DerpMagicIPAddr
-		if !isDerp && ((purpose == pingDiscovery) || (purpose == pingCLI && size == 0)) {
+		// Skip MTU probing for SCION paths — the SCION path MTU is known
+		// from metadata and oversized probes won't fit through the path.
+		if !isDerp && !ep.scionKey.IsSet() && ((purpose == pingDiscovery) || (purpose == pingCLI && size == 0)) {
 			de.c.dlogf("[v1] magicsock: starting MTU probe")
 			sizes = mtuProbePingSizesV4
 			if ep.ap.Addr().Is6() {
@@ -1374,6 +1387,10 @@ func (de *endpoint) sendDiscoPingsLocked(now mono.Time, sendCallMeMaybe bool) {
 
 		de.startDiscoPingLocked(epAddr{ap: ep}, now, pingDiscovery, 0, nil)
 	}
+	if de.sendDiscoPingsSCIONLocked(now) {
+		sentAny = true
+	}
+
 	derpAddr := de.derpAddr
 	if sentAny && sendCallMeMaybe && derpAddr.IsValid() {
 		// Have our magicsock.Conn figure out its STUN endpoint (if
@@ -1472,7 +1489,6 @@ func (de *endpoint) updateFromNode(n tailcfg.NodeView, heartbeatDisabled bool, p
 		panic("nil node when updating endpoint")
 	}
 	de.mu.Lock()
-	defer de.mu.Unlock()
 
 	de.heartbeatDisabled = heartbeatDisabled
 	if probeUDPLifetimeEnabled {
@@ -1525,6 +1541,16 @@ func (de *endpoint) updateFromNode(n tailcfg.NodeView, heartbeatDisabled bool, p
 	de.setEndpointsLocked(n.Endpoints())
 
 	de.relayCapable = capVerIsRelayCapable(n.Cap())
+
+	oldSCIONKeys := de.updateFromNodeSCIONLocked(n)
+
+	de.mu.Unlock()
+
+	// Clean up SCION paths outside de.mu. c.mu is held by caller (updateNodes),
+	// so call unregisterSCIONPath directly without re-locking.
+	for _, k := range oldSCIONKeys {
+		de.c.unregisterSCIONPath(k)
+	}
 }
 
 func (de *endpoint) setEndpointsLocked(eps interface {
@@ -1657,6 +1683,13 @@ func (de *endpoint) noteConnectivityChange() {
 // udpAddr. size is the length of the entire disco message including
 // disco headers. If size is zero, assume it is the safe wire MTU.
 func pingSizeToPktLen(size int, udpAddr epAddr) tstun.WireMTU {
+	if udpAddr.scionKey.IsSet() {
+		// SCION wire MTU is fixed regardless of ping size: the WireGuard
+		// packet must fit inside the SCION path's payload budget (path MTU
+		// minus variable SCION headers). We use a conservative value
+		// rather than computing per-path overhead from the hop count.
+		return scionWireMTU
+	}
 	if size == 0 {
 		return tstun.SafeWireMTU()
 	}
@@ -1720,9 +1753,10 @@ func (de *endpoint) handlePongConnLocked(m *disco.Pong, di *discoInfo, src epAdd
 	now := mono.Now()
 	latency := now.Sub(sp.at)
 
-	if !isDerp && !src.vni.IsSet() {
-		// Note: we check vni.isSet() as relay [epAddr]'s are not stored in
-		// endpointState, they are either de.bestAddr or not.
+	if !isDerp && !src.vni.IsSet() && !src.scionKey.IsSet() {
+		// Note: we check vni.IsSet() and scionKey.IsSet() as relay and
+		// SCION epAddr's are not stored in endpointState; they are either
+		// de.bestAddr or not.
 		st, ok := de.endpointState[sp.to.ap]
 		if !ok {
 			// This is no longer an endpoint we care about.
@@ -1739,6 +1773,11 @@ func (de *endpoint) handlePongConnLocked(m *disco.Pong, di *discoInfo, src epAdd
 		})
 	}
 
+	// Record latency for SCION paths in per-path probe state.
+	if !isDerp {
+		de.handlePongSCIONLocked(src, latency, now)
+	}
+
 	if sp.purpose != pingHeartbeat && sp.purpose != pingHeartbeatForUDPLifetime {
 		de.c.dlogf("[v1] magicsock: disco: %v<-%v (%v, %v)  got pong tx=%x latency=%v pktlen=%v pong.src=%v%v", de.c.discoAtomic.Short(), de.discoShort(), de.publicKey.ShortString(), src, m.TxID[:6], latency.Round(time.Millisecond), pktLen, m.Src, logger.ArgWriter(func(bw *bufio.Writer) {
 			if sp.to != src {
@@ -1759,24 +1798,39 @@ func (de *endpoint) handlePongConnLocked(m *disco.Pong, di *discoInfo, src epAdd
 	// TODO(bradfitz): decide how latency vs. preference order affects decision
 	if !isDerp {
 		thisPong := addrQuality{
-			epAddr:  sp.to,
-			latency: latency,
-			wireMTU: pingSizeToPktLen(sp.size, sp.to),
+			epAddr:         sp.to,
+			latency:        latency,
+			wireMTU:        pingSizeToPktLen(sp.size, sp.to),
+			scionPreferred: de.scionPreferred,
 		}
-		// TODO(jwhited): consider checking de.trustBestAddrUntil as well. If
-		//  de.bestAddr is untrusted we may want to clear it, otherwise we could
-		//  get stuck with a forever untrusted bestAddr that blackholes, since
-		//  we don't clear direct UDP paths on disco ping timeout (see
-		//  discoPingTimeout).
-		if betterAddr(thisPong, de.bestAddr) {
-			de.c.logf("magicsock: disco: node %v %v now using %v mtu=%v tx=%x", de.publicKey.ShortString(), de.discoShort(), sp.to, thisPong.wireMTU, m.TxID[:6])
-			de.debugUpdates.Add(EndpointChange{
-				When: time.Now(),
-				What: "handlePongConnLocked-bestAddr-update",
-				From: de.bestAddr,
-				To:   thisPong,
-			})
-			de.setBestAddrLocked(thisPong)
+		// If the current bestAddr is untrusted (no recent pong confirming
+		// it works), allow any fresh pong to replace it. This prevents
+		// getting stuck with a dead bestAddr that betterAddr() refuses to
+		// demote due to preference rules (e.g., TS_PREFER_SCION=1).
+		curBestUntrusted := de.bestAddr.ap.IsValid() && now.After(de.trustBestAddrUntil)
+
+		// When the current bestAddr is a trusted SCION path and this pong
+		// is from a different SCION path on the same host, skip generic
+		// betterAddr promotion. The SCION-aware reEvalSCIONPathsLocked
+		// (throttled to 2s) handles multi-path switching to avoid flapping
+		// between paths with similar latency.
+		scionToScion := thisPong.epAddr.isSCION() && de.bestAddr.isSCION() &&
+			thisPong.epAddr.ap == de.bestAddr.ap &&
+			thisPong.epAddr.scionKey != de.bestAddr.scionKey
+		skipPromotion := scionToScion && !curBestUntrusted
+
+		if !skipPromotion && (curBestUntrusted || betterAddr(thisPong, de.bestAddr)) {
+			if thisPong.epAddr != de.bestAddr.epAddr {
+				de.c.logf("magicsock: disco: node %v %v now using %v mtu=%v tx=%x", de.publicKey.ShortString(), de.discoShort(), de.scionAddrStr(sp.to), thisPong.wireMTU, m.TxID[:6])
+				de.debugUpdates.Add(EndpointChange{
+					When: time.Now(),
+					What: "handlePongConnLocked-bestAddr-update",
+					From: de.bestAddr,
+					To:   thisPong,
+				})
+				de.setBestAddrLocked(thisPong)
+				de.handlePongPromoteSCIONLocked(thisPong)
+			}
 		}
 		if de.bestAddr.epAddr == thisPong.epAddr {
 			de.debugUpdates.Add(EndpointChange{
@@ -1794,19 +1848,28 @@ func (de *endpoint) handlePongConnLocked(m *disco.Pong, di *discoInfo, src epAdd
 }
 
 // epAddr is a [netip.AddrPort] with an optional Geneve header (RFC8926)
-// [packet.VirtualNetworkID].
+// [packet.VirtualNetworkID] or SCION path key.
 type epAddr struct {
-	ap  netip.AddrPort          // if ap == tailcfg.DerpMagicIPAddr then vni is never set
-	vni packet.VirtualNetworkID // vni.IsSet() indicates if this [epAddr] involves a Geneve header
+	ap       netip.AddrPort          // if ap == tailcfg.DerpMagicIPAddr then vni is never set
+	vni      packet.VirtualNetworkID // vni.IsSet() indicates if this [epAddr] involves a Geneve header
+	scionKey scionPathKey            // non-zero if this is a SCION endpoint
 }
 
 // isDirect returns true if e.ap is valid and not tailcfg.DerpMagicIPAddr,
-// and a VNI is not set.
+// and neither a VNI nor a SCION key is set.
 func (e epAddr) isDirect() bool {
-	return e.ap.IsValid() && e.ap.Addr() != tailcfg.DerpMagicIPAddr && !e.vni.IsSet()
+	return e.ap.IsValid() && e.ap.Addr() != tailcfg.DerpMagicIPAddr && !e.vni.IsSet() && !e.scionKey.IsSet()
+}
+
+// isSCION reports whether this address represents a SCION path.
+func (e epAddr) isSCION() bool {
+	return e.scionKey.IsSet()
 }
 
 func (e epAddr) String() string {
+	if e.scionKey.IsSet() {
+		return fmt.Sprintf("%v:scion:%d", e.ap.String(), e.scionKey)
+	}
 	if !e.vni.IsSet() {
 		return e.ap.String()
 	}
@@ -1820,6 +1883,7 @@ type addrQuality struct {
 	relayServerDisco key.DiscoPublic // only relevant if epAddr.vni.isSet(), otherwise zero value
 	latency          time.Duration
 	wireMTU          tstun.WireMTU
+	scionPreferred   bool // true if both self and peer have NodeAttrSCIONPrefer
 }
 
 func (a addrQuality) String() string {
@@ -1856,6 +1920,24 @@ func betterAddr(a, b addrQuality) bool {
 		return false
 	}
 
+	// SCION beats relay (Geneve) unconditionally.
+	if a.scionKey.IsSet() && !b.scionKey.IsSet() && b.vni.IsSet() {
+		return true
+	}
+	if b.scionKey.IsSet() && !a.scionKey.IsSet() && a.vni.IsSet() {
+		return false
+	}
+
+	// When TS_PREFER_SCION=1, SCION beats everything unconditionally.
+	if preferSCION() {
+		if a.scionKey.IsSet() && !b.scionKey.IsSet() {
+			return true
+		}
+		if b.scionKey.IsSet() && !a.scionKey.IsSet() {
+			return false
+		}
+	}
+
 	// Each address starts with a set of points (from 0 to 100) that
 	// represents how much faster they are than the highest-latency
 	// endpoint. For example, if a has latency 200ms and b has latency
@@ -1900,6 +1982,22 @@ func betterAddr(a, b addrQuality) bool {
 		bPoints += 10
 	}
 
+	// SCION paths get a configurable bonus (default +15) so they win at
+	// similar latency. NodeAttrSCIONPrefer adds +25 more for a strong
+	// admin preference (total +40 at default).
+	if a.scionKey.IsSet() {
+		aPoints += scionPreferenceBonus()
+	}
+	if b.scionKey.IsSet() {
+		bPoints += scionPreferenceBonus()
+	}
+	if a.scionPreferred && a.scionKey.IsSet() {
+		aPoints += 25
+	}
+	if b.scionPreferred && b.scionKey.IsSet() {
+		bPoints += 25
+	}
+
 	// Don't change anything if the latency improvement is less than 1%; we
 	// want a bit of "stickiness" (a.k.a. hysteresis) to avoid flapping if
 	// there's two roughly-equivalent endpoints.
@@ -2016,22 +2114,35 @@ func (de *endpoint) populatePeerStatus(ps *ipnstate.PeerStatus) {
 	ps.Active = now.Sub(de.lastSendExt) < sessionActiveTimeout
 
 	if udpAddr, derpAddr, _ := de.addrForSendLocked(now); udpAddr.ap.IsValid() && !derpAddr.IsValid() {
-		if udpAddr.vni.IsSet() {
+		if udpAddr.isSCION() {
+			// Access c.scionPaths directly — c.mu is already held by
+			// our caller (Conn.UpdateStatus).
+			if pi, ok := de.c.scionPaths[udpAddr.scionKey]; ok {
+				ps.CurAddr = pi.String()
+			} else {
+				ps.CurAddr = udpAddr.String()
+			}
+		} else if udpAddr.vni.IsSet() {
 			ps.PeerRelay = udpAddr.String()
 		} else {
 			ps.CurAddr = udpAddr.String()
 		}
 	}
+	de.populateSCIONPathsLocked(ps)
 }
 
 // stopAndReset stops timers associated with de and resets its state back to zero.
 // It's called when a discovery endpoint is no longer present in the
 // NetworkMap, or when magicsock is transitioning from running to
-// stopped state (via SetPrivateKey(zero))
+// stopped state (via SetPrivateKey(zero)).
+// c.mu must be held.
 func (de *endpoint) stopAndReset() {
 	atomic.AddInt64(&de.numStopAndResetAtomic, 1)
 	de.mu.Lock()
-	defer de.mu.Unlock()
+
+	// Extract scionPathKeys before releasing de.mu so we can clean them up
+	// under c.mu afterward (lock order: c.mu before de.mu).
+	scionKeys := de.stopAndResetSCIONLocked()
 
 	if closing := de.c.closing.Load(); !closing {
 		if de.isWireguardOnly {
@@ -2050,6 +2161,13 @@ func (de *endpoint) stopAndReset() {
 		de.heartBeatTimer.Stop()
 		de.heartBeatTimer = nil
 	}
+	de.mu.Unlock()
+
+	// Clean up SCION paths outside de.mu. c.mu is held by caller
+	// (updateNodes, SetPrivateKey, Close), so call directly.
+	for _, k := range scionKeys {
+		de.c.unregisterSCIONPath(k)
+	}
 }
 
 // resetLocked clears all the endpoint's p2p state, reverting it to a
diff --git a/wgengine/magicsock/endpoint_scion.go b/wgengine/magicsock/endpoint_scion.go
new file mode 100644
index 0000000000000..3fa7f258987a6
--- /dev/null
+++ b/wgengine/magicsock/endpoint_scion.go
@@ -0,0 +1,395 @@
+// Copyright (c) Tailscale Inc & contributors
+// SPDX-License-Identifier: BSD-3-Clause
+
+//go:build !ts_omit_scion
+
+package magicsock
+
+import (
+	"cmp"
+	"slices"
+	"time"
+
+	"tailscale.com/tailcfg"
+	"tailscale.com/tstime/mono"
+)
+
+// heartbeatSCIONLocked handles SCION-specific heartbeat logic.
+// When the best address is not SCION, it heartbeats all SCION paths so they
+// can compete via betterAddr. When the best IS SCION and there are multiple
+// paths, it probes non-best paths via round-robin.
+// de.mu must be held.
+func (de *endpoint) heartbeatSCIONLocked(now mono.Time) {
+	if de.scionState == nil || de.c.pconnSCION.Load() == nil {
+		return
+	}
+	if !de.bestAddr.isSCION() {
+		// Even when the current best path is "good enough" to skip a full ping
+		// round, heartbeat all SCION paths so they can compete via betterAddr.
+		// Without this, SCION never gets pinged once a low-latency direct path
+		// suppresses wantFullPingLocked.
+		for pk, ps := range de.scionState.paths {
+			if !ps.lastPing.IsZero() && now.Sub(ps.lastPing) < discoPingInterval {
+				continue
+			}
+			ps.lastPing = now
+			ps.pingsSent++
+			scionEp := epAddr{
+				ap:       de.scionState.hostAddr,
+				scionKey: pk,
+			}
+			de.startDiscoPingLocked(scionEp, now, pingHeartbeat, 0, nil)
+		}
+	} else if len(de.scionState.paths) > 1 {
+		// Probe non-best SCION paths one at a time via round-robin so
+		// latency data stays fresh for re-evaluation.
+		de.probeSCIONNonBestLocked(now)
+	}
+}
+
+// sendDiscoPingsSCIONLocked pings all SCION paths for this peer during a
+// full discovery round. Returns true if SCION is available for this peer.
+// de.mu must be held.
+func (de *endpoint) sendDiscoPingsSCIONLocked(now mono.Time) bool {
+	if de.scionState == nil || de.c.pconnSCION.Load() == nil {
+		return false
+	}
+	for pk, ps := range de.scionState.paths {
+		if !ps.lastPing.IsZero() && now.Sub(ps.lastPing) < discoPingInterval {
+			continue
+		}
+		ps.lastPing = now
+		ps.pingsSent++
+		scionEp := epAddr{
+			ap:       de.scionState.hostAddr,
+			scionKey: pk,
+		}
+		de.startDiscoPingLocked(scionEp, now, pingDiscovery, 0, nil)
+	}
+	return true
+}
+
+// cliPingSCIONLocked pings all SCION paths when the user runs "tailscale ping".
+// de.mu must be held.
+func (de *endpoint) cliPingSCIONLocked(now mono.Time, size int, resCB *pingResultAndCallback) {
+	if de.scionState == nil || de.c.pconnSCION.Load() == nil {
+		return
+	}
+	for pk := range de.scionState.paths {
+		scionEp := epAddr{
+			ap:       de.scionState.hostAddr,
+			scionKey: pk,
+		}
+		de.startDiscoPingLocked(scionEp, now, pingCLI, size, resCB)
+	}
+}
+
+// discoPingTimeoutSCIONLocked handles disco ping timeout for SCION paths,
+// tracking consecutive loss and demoting unhealthy paths.
+// de.mu must be held.
+func (de *endpoint) discoPingTimeoutSCIONLocked(sp sentPing) {
+	if !sp.to.scionKey.IsSet() || de.scionState == nil {
+		return
+	}
+	ps, ok := de.scionState.paths[sp.to.scionKey]
+	if !ok {
+		return
+	}
+	ps.consecutiveLoss++
+	if ps.consecutiveLoss >= 3 && ps.healthy {
+		ps.healthy = false
+		de.c.logf("magicsock: SCION path %d unhealthy for %v (loss: %d)",
+			sp.to.scionKey, de.publicKey.ShortString(), ps.consecutiveLoss)
+		de.demoteSCIONPathLocked(sp.to.scionKey)
+	}
+}
+
+// handlePongSCIONLocked records a pong measurement for a SCION path and
+// triggers re-evaluation of path latencies.
+// de.mu must be held.
+func (de *endpoint) handlePongSCIONLocked(src epAddr, latency time.Duration, now mono.Time) {
+	if !src.scionKey.IsSet() || de.scionState == nil {
+		return
+	}
+	if ps, ok := de.scionState.paths[src.scionKey]; ok {
+		ps.addPongReply(scionPongReply{
+			latency: latency,
+			pongAt:  now,
+		})
+		ps.pongsReceived++
+		ps.consecutiveLoss = 0
+		if !ps.healthy {
+			ps.healthy = true
+			de.c.logf("magicsock: SCION path %d recovered for %v", src.scionKey, de.publicKey.ShortString())
+		}
+	}
+	de.reEvalSCIONPathsLocked(now)
+}
+
+// handlePongPromoteSCIONLocked updates the SCION activePath after bestAddr
+// switches to a SCION path via pong promotion.
+// de.mu must be held.
+func (de *endpoint) handlePongPromoteSCIONLocked(thisPong addrQuality) {
+	if !thisPong.epAddr.scionKey.IsSet() || de.scionState == nil {
+		return
+	}
+	de.scionState.activePath = thisPong.epAddr.scionKey
+	go de.c.updateActiveSCIONPathLocking(de.scionState.peerIA, de.scionState.hostAddr, thisPong.epAddr.scionKey)
+}
+
+// updateFromNodeSCIONLocked handles the SCION-specific parts of updateFromNode:
+// detects new/changed SCION service advertisements, triggers path discovery,
+// and computes SCION preference. Returns old SCION path keys that need cleanup
+// outside de.mu (lock order: c.mu before de.mu).
+// de.mu must be held.
+func (de *endpoint) updateFromNodeSCIONLocked(n tailcfg.NodeView) []scionPathKey {
+	var oldSCIONKeys []scionPathKey
+	if peerIA, hostAddr, ok := scionServiceFromPeer(n); ok {
+		if de.scionState == nil || de.scionState.peerIA != peerIA || de.scionState.hostAddr != hostAddr {
+			// New or changed SCION address — discover paths asynchronously
+			// to avoid blocking updateFromNode (which holds the endpoint lock).
+			if de.c.pconnSCION.Load() != nil {
+				de.c.logf("magicsock: SCION peer %s at %s, discovering paths...", peerIA, hostAddr)
+				go de.discoverSCIONPathAsync(peerIA, hostAddr)
+			} else {
+				de.c.logf("magicsock: peer has SCION (%s) but local SCION not available", peerIA)
+			}
+		}
+	} else if de.scionState != nil {
+		// Peer no longer advertises SCION.
+		for k := range de.scionState.paths {
+			oldSCIONKeys = append(oldSCIONKeys, k)
+		}
+		de.scionState = nil
+	}
+
+	// Check if SCION should be preferred for this peer.
+	peerSCIONPrefer := n.CapMap().Contains(tailcfg.NodeAttrSCIONPrefer)
+	selfSCIONPrefer := de.c.self.Valid() && de.c.self.CapMap().Contains(tailcfg.NodeAttrSCIONPrefer)
+	de.scionPreferred = peerSCIONPrefer && selfSCIONPrefer && de.scionState != nil
+
+	return oldSCIONKeys
+}
+
+// stopAndResetSCIONLocked extracts SCION path keys for cleanup before the
+// endpoint state is cleared. Returns keys that need cleanup outside de.mu.
+// de.mu must be held.
+func (de *endpoint) stopAndResetSCIONLocked() []scionPathKey {
+	if de.scionState == nil {
+		return nil
+	}
+	var keys []scionPathKey
+	for k := range de.scionState.paths {
+		keys = append(keys, k)
+	}
+	de.scionState = nil
+	return keys
+}
+
+// sendSCIONData sends WireGuard data over a SCION path, handling error
+// recovery (re-discovery) and metrics. Called from send() after de.mu is released.
+func (de *endpoint) sendSCIONData(udpAddr epAddr, buffs [][]byte, offset int) error {
+	_, err := de.c.sendSCIONBatch(udpAddr, buffs, offset)
+	if err != nil {
+		de.noteBadEndpoint(udpAddr)
+		// Trigger re-discovery so we don't wait up to 30s for the
+		// periodic refreshSCIONPaths to fix an expired path.
+		// discoverSCIONPathAsync self-throttles to once per 5s.
+		de.mu.Lock()
+		st := de.scionState
+		de.mu.Unlock()
+		if st != nil {
+			go de.discoverSCIONPathAsync(st.peerIA, st.hostAddr)
+		}
+	} else if de.c.metrics != nil {
+		var txBytes int
+		for _, b := range buffs {
+			txBytes += len(b[offset:])
+		}
+		de.c.metrics.outboundPacketsSCIONTotal.Add(int64(len(buffs)))
+		de.c.metrics.outboundBytesSCIONTotal.Add(int64(txBytes))
+	}
+	return err
+}
+
+// probeSCIONNonBestLocked probes one non-active SCION path per call using
+// round-robin ordering. This keeps latency data fresh for paths that aren't
+// currently the active path, enabling re-evaluation to detect better options.
+// de.mu must be held.
+func (de *endpoint) probeSCIONNonBestLocked(now mono.Time) {
+	if de.scionState == nil {
+		return
+	}
+
+	// Collect non-active path keys and sort for deterministic ordering.
+	var nonBest []scionPathKey
+	for k := range de.scionState.paths {
+		if k != de.scionState.activePath {
+			nonBest = append(nonBest, k)
+		}
+	}
+	if len(nonBest) == 0 {
+		return
+	}
+	slices.SortFunc(nonBest, func(a, b scionPathKey) int {
+		return cmp.Compare(a, b)
+	})
+
+	// Pick one via round-robin.
+	idx := de.scionState.probeRoundRobin % len(nonBest)
+	de.scionState.probeRoundRobin++
+	pk := nonBest[idx]
+	ps := de.scionState.paths[pk]
+
+	// Rate limit per path.
+	if !ps.lastPing.IsZero() && now.Sub(ps.lastPing) < discoPingInterval {
+		return
+	}
+	ps.lastPing = now
+	ps.pingsSent++
+	scionEp := epAddr{
+		ap:       de.scionState.hostAddr,
+		scionKey: pk,
+	}
+	de.startDiscoPingLocked(scionEp, now, pingHeartbeat, 0, nil)
+}
+
+// demoteSCIONPathLocked is called when a SCION path is marked unhealthy.
+// It finds the best remaining healthy path by measured latency and switches
+// activePath and bestAddr if the demoted path was active/best.
+// de.mu must be held.
+func (de *endpoint) demoteSCIONPathLocked(demotedKey scionPathKey) {
+	if de.scionState == nil {
+		return
+	}
+
+	// Find best healthy path by measured latency.
+	var bestKey scionPathKey
+	var bestLatency time.Duration
+	for k, ps := range de.scionState.paths {
+		if k == demotedKey || !ps.healthy {
+			continue
+		}
+		lat := ps.latency()
+		if !bestKey.IsSet() || lat < bestLatency {
+			bestKey = k
+			bestLatency = lat
+		}
+	}
+
+	// Only act if the demoted path was the active path.
+	if de.scionState.activePath != demotedKey {
+		return
+	}
+
+	if bestKey.IsSet() {
+		de.scionState.activePath = bestKey
+		newAddr := addrQuality{
+			epAddr:         epAddr{ap: de.scionState.hostAddr, scionKey: bestKey},
+			latency:        bestLatency,
+			wireMTU:        scionWireMTU,
+			scionPreferred: de.scionPreferred,
+		}
+		de.c.logf("magicsock: SCION path demoted, switching to %s for %v", de.scionAddrStr(newAddr.epAddr), de.publicKey.ShortString())
+		de.setBestAddrLocked(newAddr)
+		go de.c.updateActiveSCIONPathLocking(de.scionState.peerIA, de.scionState.hostAddr, bestKey)
+	} else {
+		// No healthy SCION paths remain. Clear SCION bestAddr to fall back.
+		de.scionState.activePath = 0
+		if de.bestAddr.isSCION() {
+			de.c.logf("magicsock: no healthy SCION paths for %v, clearing bestAddr", de.publicKey.ShortString())
+			de.clearBestAddrLocked()
+		}
+	}
+}
+
+// scionReEvalInterval is the minimum time between SCION path re-evaluations.
+const scionReEvalInterval = 2 * time.Second
+
+// reEvalSCIONPathsLocked re-evaluates all SCION paths by measured latency
+// after a pong is recorded. Throttled to scionReEvalInterval. If a healthier,
+// lower-latency path is found, switches bestAddr and activePath. Incumbent
+// bias prevents flapping between paths with similar latency.
+// de.mu must be held.
+func (de *endpoint) reEvalSCIONPathsLocked(now mono.Time) {
+	if de.scionState == nil || len(de.scionState.paths) < 2 {
+		return
+	}
+	if !de.scionState.lastFullEvalAt.IsZero() && now.Sub(de.scionState.lastFullEvalAt) < scionReEvalInterval {
+		return
+	}
+	de.scionState.lastFullEvalAt = now
+
+	// Check all paths have at least 1 pong measurement.
+	for _, ps := range de.scionState.paths {
+		if ps.pongCount == 0 {
+			return
+		}
+	}
+
+	// Find the healthy path with lowest measured latency.
+	var bestKey scionPathKey
+	var bestLatency time.Duration
+	for k, ps := range de.scionState.paths {
+		if !ps.healthy {
+			continue
+		}
+		lat := ps.latency()
+		if !bestKey.IsSet() || lat < bestLatency {
+			bestKey = k
+			bestLatency = lat
+		}
+	}
+
+	if !bestKey.IsSet() || bestKey == de.scionState.activePath {
+		return
+	}
+
+	// Require meaningful improvement over active path to avoid flapping
+	// between paths with similar latency. The candidate must be ≥20% faster
+	// or ≥2ms faster (whichever threshold is smaller).
+	if activePS, ok := de.scionState.paths[de.scionState.activePath]; ok && activePS.healthy {
+		activeLat := activePS.latency()
+		threshold := activeLat / 5 // 20%
+		if minThreshold := 2 * time.Millisecond; threshold < minThreshold {
+			threshold = minThreshold
+		}
+		if activeLat-bestLatency < threshold {
+			return
+		}
+	}
+
+	candidate := addrQuality{
+		epAddr:         epAddr{ap: de.scionState.hostAddr, scionKey: bestKey},
+		latency:        bestLatency,
+		wireMTU:        scionWireMTU,
+		scionPreferred: de.scionPreferred,
+	}
+
+	if betterAddr(candidate, de.bestAddr) {
+		de.c.logf("magicsock: SCION re-eval: switching to %s (latency %v) for %v",
+			de.scionAddrStr(candidate.epAddr), bestLatency.Round(time.Millisecond), de.publicKey.ShortString())
+		de.debugUpdates.Add(EndpointChange{
+			When: time.Now(),
+			What: "reEvalSCIONPathsLocked-switch",
+			From: de.bestAddr,
+			To:   candidate,
+		})
+		de.setBestAddrLocked(candidate)
+		de.scionState.activePath = bestKey
+		go de.c.updateActiveSCIONPathLocking(de.scionState.peerIA, de.scionState.hostAddr, bestKey)
+	}
+}
+
+// scionAddrStr returns a human-readable string for a SCION epAddr using
+// cached path info from de.scionState. Falls back to e.String().
+// de.mu must be held.
+func (de *endpoint) scionAddrStr(e epAddr) string {
+	if !e.scionKey.IsSet() || de.scionState == nil {
+		return e.String()
+	}
+	if ps, ok := de.scionState.paths[e.scionKey]; ok && ps.displayStr != "" {
+		return ps.displayStr
+	}
+	return e.String()
+}
diff --git a/wgengine/magicsock/magicsock.go b/wgengine/magicsock/magicsock.go
index f61e85b37fcec..34797d9ee7497 100644
--- a/wgengine/magicsock/magicsock.go
+++ b/wgengine/magicsock/magicsock.go
@@ -96,8 +96,16 @@ const (
 	PathDERP          Path = "derp"
 	PathPeerRelayIPv4 Path = "peer_relay_ipv4"
 	PathPeerRelayIPv6 Path = "peer_relay_ipv6"
+	PathSCION         Path = "scion"
 )
 
+// SCIONConfig holds runtime-configurable SCION parameters.
+type SCIONConfig struct {
+	Enabled      bool
+	BootstrapURL string
+	Prefer       bool
+}
+
 type pathLabel struct {
 	// Path indicates the path that the packet took:
 	// - direct_ipv4
@@ -146,6 +154,12 @@ type metrics struct {
 	outboundBytesPeerRelayIPv4Total expvar.Int
 	outboundBytesPeerRelayIPv6Total expvar.Int
 
+	// SCION path counters.
+	inboundPacketsSCIONTotal  expvar.Int
+	inboundBytesSCIONTotal    expvar.Int
+	outboundPacketsSCIONTotal expvar.Int
+	outboundBytesSCIONTotal   expvar.Int
+
 	// outboundPacketsDroppedErrors is the total number of outbound packets
 	// dropped due to errors.
 	outboundPacketsDroppedErrors expvar.Int
@@ -163,10 +177,11 @@ type Conn struct {
 	derpActiveFunc         func()
 	idleFunc               func() time.Duration // nil means unknown
 	testOnlyPacketListener nettype.PacketListener
-	noteRecvActivity       func(key.NodePublic) // or nil, see Options.NoteRecvActivity
-	netMon                 *netmon.Monitor      // must be non-nil
-	health                 *health.Tracker      // or nil
-	controlKnobs           *controlknobs.Knobs  // or nil
+	noteRecvActivity       func(key.NodePublic)                   // or nil, see Options.NoteRecvActivity
+	onDERPRecv             func(int, key.NodePublic, []byte) bool // or nil, see Options.OnDERPRecv
+	netMon                 *netmon.Monitor                        // must be non-nil
+	health                 *health.Tracker                        // or nil
+	controlKnobs           *controlknobs.Knobs                    // or nil
 
 	// ================================================================
 	// No locking required to access these fields, either because
@@ -187,6 +202,11 @@ type Conn struct {
 	pconn4 RebindingUDPConn
 	pconn6 RebindingUDPConn
 
+	// pconnSCION is the SCION connection, nil if SCION is not available.
+	// Accessed atomically from hot-path send/receive goroutines;
+	// writes happen under c.mu for higher-level coordination.
+	pconnSCION atomic.Pointer[scionConn]
+
 	receiveBatchPool sync.Pool
 
 	// closeDisco4 and closeDisco6 are io.Closers to shut down the raw
@@ -408,6 +428,18 @@ type Conn struct {
 	// homeDERPGauge is the usermetric gauge for the home DERP region ID.
 	// This can be nil when [Options.Metrics] are not enabled.
 	homeDERPGauge *usermetric.Gauge
+
+	// scionPaths is the registry of SCION path information, keyed by
+	// scionPathKey. Each entry holds the full SCION address and path
+	// data for a peer.
+	scionPaths         map[scionPathKey]*scionPathInfo
+	scionPathsByAddr   map[scionAddrKey]scionPathKey // reverse index for O(1) lookup
+	scionPathSeq       atomic.Uint32                 // monotonic key generator for scionPaths
+	scionSoftRefreshAt map[scionIAKey]time.Time       // last soft refresh per peer, guarded by c.mu; bounded by unique peer count
+
+	// lastSCIONRecv is the last time we received any SCION packet (monotonic).
+	// Used by receiveSCION to detect a dead socket and trigger reconnection.
+	lastSCIONRecv mono.Time
 }
 
 // SetDebugLoggingEnabled controls whether spammy debug logging is enabled.
@@ -502,6 +534,13 @@ type Options struct {
 	// leave it zero, in which case a new disco key is generated per
 	// Tailscale start and kept only in memory.
 	ForceDiscoKey key.DiscoPrivate
+
+	// OnDERPRecv, if non-nil, is called for every non-disco packet
+	// received from DERP before the peer map lookup. If it returns
+	// true, the packet is considered handled and is not passed to
+	// WireGuard. The pkt slice is borrowed and must be copied if
+	// the callee needs to retain it.
+	OnDERPRecv func(regionID int, src key.NodePublic, pkt []byte) bool
 }
 
 func (o *Options) logf() logger.Logf {
@@ -640,6 +679,7 @@ func NewConn(opts Options) (*Conn, error) {
 	c.idleFunc = opts.IdleFunc
 	c.testOnlyPacketListener = opts.TestOnlyPacketListener
 	c.noteRecvActivity = opts.NoteRecvActivity
+	c.onDERPRecv = opts.OnDERPRecv
 
 	// Set up publishers and subscribers. Subscribe calls must return before
 	// NewConn otherwise published events can be missed.
@@ -723,6 +763,7 @@ func registerMetrics(reg *usermetric.Registry) *metrics {
 	pathDERP := pathLabel{Path: PathDERP}
 	pathPeerRelayV4 := pathLabel{Path: PathPeerRelayIPv4}
 	pathPeerRelayV6 := pathLabel{Path: PathPeerRelayIPv6}
+	pathSCION := pathLabel{Path: PathSCION}
 	inboundPacketsTotal := usermetric.NewMultiLabelMapWithRegistry[pathLabel](
 		reg,
 		"tailscaled_inbound_packets_total",
@@ -777,30 +818,38 @@ func registerMetrics(reg *usermetric.Registry) *metrics {
 	metricSendDERP.Register(&m.outboundPacketsDERPTotal)
 	metricSendPeerRelay.Register(&m.outboundPacketsPeerRelayIPv4Total)
 	metricSendPeerRelay.Register(&m.outboundPacketsPeerRelayIPv6Total)
+	metricRecvDataPacketsSCION.Register(&m.inboundPacketsSCIONTotal)
+	metricRecvDataBytesSCION.Register(&m.inboundBytesSCIONTotal)
+	metricSendDataPacketsSCION.Register(&m.outboundPacketsSCIONTotal)
+	metricSendDataBytesSCION.Register(&m.outboundBytesSCIONTotal)
 
 	inboundPacketsTotal.Set(pathDirectV4, &m.inboundPacketsIPv4Total)
 	inboundPacketsTotal.Set(pathDirectV6, &m.inboundPacketsIPv6Total)
 	inboundPacketsTotal.Set(pathDERP, &m.inboundPacketsDERPTotal)
 	inboundPacketsTotal.Set(pathPeerRelayV4, &m.inboundPacketsPeerRelayIPv4Total)
 	inboundPacketsTotal.Set(pathPeerRelayV6, &m.inboundPacketsPeerRelayIPv6Total)
+	inboundPacketsTotal.Set(pathSCION, &m.inboundPacketsSCIONTotal)
 
 	inboundBytesTotal.Set(pathDirectV4, &m.inboundBytesIPv4Total)
 	inboundBytesTotal.Set(pathDirectV6, &m.inboundBytesIPv6Total)
 	inboundBytesTotal.Set(pathDERP, &m.inboundBytesDERPTotal)
 	inboundBytesTotal.Set(pathPeerRelayV4, &m.inboundBytesPeerRelayIPv4Total)
 	inboundBytesTotal.Set(pathPeerRelayV6, &m.inboundBytesPeerRelayIPv6Total)
+	inboundBytesTotal.Set(pathSCION, &m.inboundBytesSCIONTotal)
 
 	outboundPacketsTotal.Set(pathDirectV4, &m.outboundPacketsIPv4Total)
 	outboundPacketsTotal.Set(pathDirectV6, &m.outboundPacketsIPv6Total)
 	outboundPacketsTotal.Set(pathDERP, &m.outboundPacketsDERPTotal)
 	outboundPacketsTotal.Set(pathPeerRelayV4, &m.outboundPacketsPeerRelayIPv4Total)
 	outboundPacketsTotal.Set(pathPeerRelayV6, &m.outboundPacketsPeerRelayIPv6Total)
+	outboundPacketsTotal.Set(pathSCION, &m.outboundPacketsSCIONTotal)
 
 	outboundBytesTotal.Set(pathDirectV4, &m.outboundBytesIPv4Total)
 	outboundBytesTotal.Set(pathDirectV6, &m.outboundBytesIPv6Total)
 	outboundBytesTotal.Set(pathDERP, &m.outboundBytesDERPTotal)
 	outboundBytesTotal.Set(pathPeerRelayV4, &m.outboundBytesPeerRelayIPv4Total)
 	outboundBytesTotal.Set(pathPeerRelayV6, &m.outboundBytesPeerRelayIPv6Total)
+	outboundBytesTotal.Set(pathSCION, &m.outboundBytesSCIONTotal)
 
 	outboundPacketsDroppedErrors.Set(usermetric.DropLabels{Reason: usermetric.ReasonError}, &m.outboundPacketsDroppedErrors)
 
@@ -833,6 +882,10 @@ func deregisterMetrics() {
 	metricSendUDP.UnregisterAll()
 	metricSendDERP.UnregisterAll()
 	metricSendPeerRelay.UnregisterAll()
+	metricRecvDataPacketsSCION.UnregisterAll()
+	metricRecvDataBytesSCION.UnregisterAll()
+	metricSendDataPacketsSCION.UnregisterAll()
+	metricSendDataBytesSCION.UnregisterAll()
 }
 
 // InstallCaptureHook installs a callback which is called to
@@ -1156,7 +1209,13 @@ func (c *Conn) Ping(peer tailcfg.NodeView, res *ipnstate.PingResult, size int, c
 func (c *Conn) populateCLIPingResponseLocked(res *ipnstate.PingResult, latency time.Duration, ep epAddr) {
 	res.LatencySeconds = latency.Seconds()
 	if ep.ap.Addr() != tailcfg.DerpMagicIPAddr {
-		if ep.vni.IsSet() {
+		if ep.isSCION() {
+			if pi, ok := c.scionPaths[ep.scionKey]; ok {
+				res.Endpoint = pi.String()
+			} else {
+				res.Endpoint = ep.String()
+			}
+		} else if ep.vni.IsSet() {
 			res.PeerRelay = ep.String()
 		} else {
 			res.Endpoint = ep.String()
@@ -1964,6 +2023,8 @@ func (c *Conn) sendDiscoMessage(dst epAddr, dstKey key.NodePublic, dstDisco key.
 
 	if isDERP {
 		metricSendDiscoDERP.Add(1)
+	} else if dst.scionKey.IsSet() {
+		metricSendDiscoSCION.Add(1)
 	} else {
 		metricSendDiscoUDP.Add(1)
 	}
@@ -1971,7 +2032,11 @@ func (c *Conn) sendDiscoMessage(dst epAddr, dstKey key.NodePublic, dstDisco key.
 	box := di.sharedKey.Seal(m.AppendMarshal(nil))
 	pkt = append(pkt, box...)
 	const isDisco = true
-	sent, err = c.sendAddr(dst.ap, dstKey, pkt, isDisco, dst.vni.IsSet())
+	if dst.scionKey.IsSet() {
+		sent, err = c.sendSCION(dst.scionKey, pkt)
+	} else {
+		sent, err = c.sendAddr(dst.ap, dstKey, pkt, isDisco, dst.vni.IsSet())
+	}
 	if sent {
 		if logLevel == discoLog || (logLevel == discoVerboseLog && debugDisco()) {
 			node := "?"
@@ -1982,6 +2047,8 @@ func (c *Conn) sendDiscoMessage(dst epAddr, dstKey key.NodePublic, dstDisco key.
 		}
 		if isDERP {
 			metricSentDiscoDERP.Add(1)
+		} else if dst.scionKey.IsSet() {
+			metricSentDiscoSCION.Add(1)
 		} else {
 			metricSentDiscoUDP.Add(1)
 		}
@@ -2511,6 +2578,12 @@ func (c *Conn) handlePingLocked(dm *disco.Ping, src epAddr, di *discoInfo, derpN
 	if nk, ok := c.unambiguousNodeKeyOfPingLocked(dm, di.discoKey, derpNodeSrc); ok {
 		if !isDerp {
 			c.peerMap.setNodeKeyForEpAddr(src, nk)
+			// For SCION sources, also register the plain host addr
+			// so WireGuard data packets (which don't carry a scionKey)
+			// can be looked up in the peerMap.
+			if src.scionKey.IsSet() {
+				c.peerMap.setNodeKeyForEpAddr(epAddr{ap: src.ap}, nk)
+			}
 		}
 	}
 
@@ -3271,6 +3344,10 @@ func (c *connBind) Open(ignoredPort uint16) ([]conn.ReceiveFunc, uint16, error)
 	if runtime.GOOS == "js" {
 		fns = []conn.ReceiveFunc{c.receiveDERP}
 	}
+	// Always register SCION receive funcs so they're available when
+	// SCION connects mid-session (e.g. via ReconfigureSCION from Android).
+	// receiveSCION handles nil pconnSCION by waiting and retrying.
+	fns = append(fns, c.receiveSCION, c.receiveSCIONShim)
 	// TODO: Combine receiveIPv4 and receiveIPv6 and receiveIP into a single
 	// closure that closes over a *RebindingUDPConn?
 	return fns, c.LocalPort(), nil
@@ -3303,6 +3380,7 @@ func (c *connBind) Close() error {
 	if c.closeDisco6 != nil {
 		c.closeDisco6.Close()
 	}
+	c.closeSCIONBindLocked()
 	// Send an empty read result to unblock receiveDERP,
 	// which will then check connBind.Closed.
 	// connBind.Closed takes c.mu, but c.derpRecvCh is buffered.
@@ -3353,6 +3431,7 @@ func (c *Conn) Close() error {
 	// They will frequently have been closed already by a call to connBind.Close.
 	c.pconn6.Close()
 	c.pconn4.Close()
+	c.closeSCIONLocked()
 	if c.closeDisco4 != nil {
 		c.closeDisco4.Close()
 	}
@@ -3600,6 +3679,9 @@ func (c *Conn) rebind(curPortFate currentPortFate) error {
 		c.portMapper.SetLocalPort(c.LocalPort())
 	}
 	c.UpdatePMTUD()
+
+	c.initSCIONLocked(c.connCtx)
+
 	return nil
 }
 
@@ -4003,11 +4085,19 @@ var (
 	metricSendDataBytesPeerRelayIPv4 = clientmetric.NewAggregateCounter("magicsock_send_data_bytes_peer_relay_ipv4")
 	metricSendDataBytesPeerRelayIPv6 = clientmetric.NewAggregateCounter("magicsock_send_data_bytes_peer_relay_ipv6")
 
+	// SCION data packets and bytes
+	metricRecvDataPacketsSCION = clientmetric.NewAggregateCounter("magicsock_recv_data_scion")
+	metricRecvDataBytesSCION  = clientmetric.NewAggregateCounter("magicsock_recv_data_bytes_scion")
+	metricSendDataPacketsSCION = clientmetric.NewAggregateCounter("magicsock_send_data_scion")
+	metricSendDataBytesSCION   = clientmetric.NewAggregateCounter("magicsock_send_data_bytes_scion")
+
 	// Disco packets
 	metricSendDiscoUDP                           = clientmetric.NewCounter("magicsock_disco_send_udp")
 	metricSendDiscoDERP                          = clientmetric.NewCounter("magicsock_disco_send_derp")
+	metricSendDiscoSCION                         = clientmetric.NewCounter("magicsock_disco_send_scion")
 	metricSentDiscoUDP                           = clientmetric.NewCounter("magicsock_disco_sent_udp")
 	metricSentDiscoDERP                          = clientmetric.NewCounter("magicsock_disco_sent_derp")
+	metricSentDiscoSCION                         = clientmetric.NewCounter("magicsock_disco_sent_scion")
 	metricSentDiscoPing                          = clientmetric.NewCounter("magicsock_disco_sent_ping")
 	metricSentDiscoPong                          = clientmetric.NewCounter("magicsock_disco_sent_pong")
 	metricSentDiscoPeerMTUProbes                 = clientmetric.NewCounter("magicsock_disco_sent_peer_mtu_probes")
diff --git a/wgengine/magicsock/magicsock_scion.go b/wgengine/magicsock/magicsock_scion.go
new file mode 100644
index 0000000000000..336ff76628df3
--- /dev/null
+++ b/wgengine/magicsock/magicsock_scion.go
@@ -0,0 +1,2786 @@
+// Copyright (c) Tailscale Inc & contributors
+// SPDX-License-Identifier: BSD-3-Clause
+
+//go:build !ts_omit_scion
+
+package magicsock
+
+import (
+	"context"
+	"encoding/binary"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"net"
+	"net/netip"
+	"os"
+	"path/filepath"
+	"slices"
+	"sort"
+	"strings"
+	"sync"
+	"time"
+
+	"github.com/gopacket/gopacket"
+	"github.com/scionproto/scion/pkg/addr"
+	"github.com/scionproto/scion/pkg/daemon"
+	"github.com/scionproto/scion/pkg/slayers"
+	scionpath "github.com/scionproto/scion/pkg/slayers/path/scion"
+	"github.com/scionproto/scion/pkg/snet"
+	"github.com/scionproto/scion/pkg/snet/addrutil"
+	snetpath "github.com/scionproto/scion/pkg/snet/path"
+	wgconn "github.com/tailscale/wireguard-go/conn"
+	"golang.org/x/net/ipv4"
+	"golang.org/x/net/ipv6"
+	"tailscale.com/envknob"
+	"tailscale.com/ipn/ipnstate"
+	"tailscale.com/net/netmon"
+	"tailscale.com/net/netns"
+	"tailscale.com/net/tstun"
+	"tailscale.com/tailcfg"
+	"tailscale.com/tstime/mono"
+	"tailscale.com/types/key"
+	"tailscale.com/types/logger"
+	"tailscale.com/util/mak"
+)
+
+// debugSCIONPreference is the TS_SCION_PREFERENCE envknob controlling the
+// betterAddr points bonus for SCION paths. Default 15; set to 0 to disable.
+var debugSCIONPreference = envknob.RegisterInt("TS_SCION_PREFERENCE")
+
+// preferSCION reports whether TS_PREFER_SCION=1 is set, which makes SCION
+// paths unconditionally preferred over all other path types (direct, relay).
+// Other paths are only used if no SCION path is available.
+var preferSCION = envknob.RegisterBool("TS_PREFER_SCION")
+
+// scionDispatcherPort is the legacy SCION dispatcher port. Older deployments
+// redirect all SCION traffic to this port instead of delivering to application
+// ports directly.
+const scionDispatcherPort = 30041
+
+var (
+	scionDaemonAddress = envknob.RegisterString("SCION_DAEMON_ADDRESS")
+	scionPort          = envknob.RegisterString("TS_SCION_PORT")
+	scionListenAddrEnv = envknob.RegisterString("TS_SCION_LISTEN_ADDR")
+	noDispatcherShim   = envknob.RegisterBool("TS_SCION_NO_DISPATCHER_SHIM")
+	scionNoFastPath    = envknob.RegisterBool("TS_SCION_NO_FAST_PATH")
+)
+
+// scionPreferenceBonus returns the betterAddr points bonus for SCION paths.
+// Returns the value of TS_SCION_PREFERENCE if set, otherwise defaults to 15.
+func scionPreferenceBonus() int {
+	if v := debugSCIONPreference(); v != 0 {
+		return v
+	}
+	if v, ok := envknob.LookupInt("TS_SCION_PREFERENCE"); ok {
+		return v // allow explicit 0
+	}
+	return 15
+}
+
+// scionIAKey is a type alias for addr.IA, used in Conn fields shared with
+// the ts_omit_scion omit file (which defines scionIAKey = uint64).
+type scionIAKey = addr.IA
+
+// scionPathKey is a compact index into the Conn-level scionPaths registry.
+// This keeps epAddr small and comparable (snet.UDPAddr contains slices).
+// A zero value means "not a SCION path."
+type scionPathKey uint32
+
+// IsSet reports whether k refers to a valid SCION path entry.
+func (k scionPathKey) IsSet() bool { return k != 0 }
+
+// scionAddrKey is a comparable key for the reverse index from (IA, host:port)
+// to scionPathKey, enabling O(1) lookup in receiveSCION.
+type scionAddrKey struct {
+	ia   addr.IA
+	addr netip.AddrPort
+}
+
+// scionPathInfo holds the full SCION path information for a peer, indexed by
+// scionPathKey. The actual SCION address and path data live here rather than
+// in epAddr to keep epAddr comparable and small.
+type scionPathInfo struct {
+	peerIA           addr.IA
+	hostAddr         netip.AddrPort       // peer's SCION host IP:port
+	fingerprint      snet.PathFingerprint // SHA256 of interface sequence; for matching across refreshes
+	path             snet.Path            // current best SCION path to this peer
+	replyPath        *snet.UDPAddr        // bootstrapped from incoming packet (pre-reversed)
+	cachedDst        *snet.UDPAddr        // pre-built destination addr; rebuilt when path changes
+	fastPath         *scionFastPath       // pre-serialized header template for fast sends
+	expiry           time.Time            // path expiration from path metadata
+	mtu              uint16               // SCION payload MTU from path metadata
+	refreshMissCount int                  // consecutive refresh cycles fingerprint absent from daemon
+	displayStr       string               // pre-computed human-readable path string
+	mu               sync.Mutex
+}
+
+// String returns the pre-computed human-readable display string for this path.
+// Format: scion:[srcIA ifid>ifid transitIA ... dstIA]:[host]:port
+func (pi *scionPathInfo) String() string {
+	return pi.displayStr
+}
+
+// buildDisplayStr pre-computes the human-readable display string from the
+// current path metadata and host address. Must be called with pi.mu held
+// (or before the info is shared), and whenever the path is updated.
+func (pi *scionPathInfo) buildDisplayStr() {
+	hops := "?"
+	if pi.path != nil {
+		if md := pi.path.Metadata(); md != nil && len(md.Interfaces) > 0 {
+			hops = formatSCIONHops(md.Interfaces)
+		}
+	}
+	pi.displayStr = fmt.Sprintf("scion:[%s]:[%s]:%d",
+		hops, pi.hostAddr.Addr(), pi.hostAddr.Port())
+}
+
+// formatSCIONHops formats SCION path interfaces into standard hop notation.
+// Produces: "19-ffaa:1:eba 2>2 19-ffaa:1:bf5" for a 2-hop path.
+// Mirrors the format used by snet/path.fmtInterfaces and `scion showpaths`.
+func formatSCIONHops(ifaces []snet.PathInterface) string {
+	if len(ifaces) == 0 {
+		return "?"
+	}
+	if len(ifaces) == 1 {
+		// Single interface shouldn't occur in valid SCION paths
+		// (interfaces always come in pairs), but handle gracefully.
+		return fmt.Sprintf("%s %d", ifaces[0].IA, ifaces[0].ID)
+	}
+	var sb strings.Builder
+	// First interface: srcIA ifid
+	fmt.Fprintf(&sb, "%s %d", ifaces[0].IA, ifaces[0].ID)
+	// Middle interfaces come in pairs: entry-ifid transitIA exit-ifid
+	for i := 1; i < len(ifaces)-1; i += 2 {
+		fmt.Fprintf(&sb, ">%d %s %d", ifaces[i].ID, ifaces[i].IA, ifaces[i+1].ID)
+	}
+	// Last interface: ifid dstIA
+	last := ifaces[len(ifaces)-1]
+	fmt.Fprintf(&sb, ">%d %s", last.ID, last.IA)
+	return sb.String()
+}
+
+// buildCachedDst constructs the cached destination address from the current
+// path info. Must be called with pi.mu held (or before the info is shared).
+func (pi *scionPathInfo) buildCachedDst() {
+	dst := &snet.UDPAddr{
+		IA: pi.peerIA,
+		Host: &net.UDPAddr{
+			IP:   pi.hostAddr.Addr().AsSlice(),
+			Port: int(pi.hostAddr.Port()),
+		},
+	}
+	if pi.path != nil {
+		dst.Path = pi.path.Dataplane()
+		dst.NextHop = pi.path.UnderlayNextHop()
+	}
+	pi.cachedDst = dst
+}
+
+// The SCION path metadata MTU is the maximum SCION packet size that can
+// traverse the path (including all SCION headers but excluding underlay
+// IP+UDP). The actual payload budget depends on the variable-length path
+// header, which grows with hop count:
+//   - SCION common header: 12 bytes
+//   - Address header (IPv4, 2x ISD-AS + 2x IPv4): 24 bytes
+//   - Path header: ~36 bytes (2 hops) to ~96 bytes (6+ hops)
+//   - SCION/UDP L4 header: 8 bytes
+//
+// Rather than computing exact overhead per path, we use a conservative
+// wire MTU of 1280 bytes (the minimum IPv6 link MTU). This guarantees
+// WireGuard packets fit within any SCION path's payload budget regardless
+// of hop count.
+const scionWireMTU = tstun.WireMTU(1280)
+
+// scionUnsetHopLatency is the assumed per-hop latency when the SCION daemon
+// reports LatencyUnset for a hop. Conservative estimate for path selection.
+const scionUnsetHopLatency = 10 * time.Millisecond
+
+// scionDaemonProbeTimeout is the timeout for probing the SCION daemon
+// connector to check if it's still alive (used for tiered reconnection).
+const scionDaemonProbeTimeout = 5 * time.Second
+
+// defaultSCIONProbePaths is the default number of SCION paths to probe per peer.
+const defaultSCIONProbePaths = 5
+
+// scionStalePathThreshold is the number of consecutive refresh cycles a
+// fingerprint must be absent from daemon results before the path is removed.
+// At the default 30s refresh interval, this is ~90s.
+const scionStalePathThreshold = 3
+
+// scionPongHistoryCount is the ring buffer size for per-path pong latency tracking.
+const scionPongHistoryCount = 8
+
+// scionMaxProbePaths returns the max number of SCION paths to probe per peer.
+// Defaults to 5, overridable via TS_SCION_MAX_PROBE_PATHS.
+func scionMaxProbePaths() int {
+	if v, ok := envknob.LookupInt("TS_SCION_MAX_PROBE_PATHS"); ok && v > 0 {
+		return v
+	}
+	return defaultSCIONProbePaths
+}
+
+// scionEndpointState tracks SCION-specific per-peer state on an endpoint.
+type scionEndpointState struct {
+	peerIA          addr.IA                               // peer's ISD-AS from Services advertisement
+	hostAddr        netip.AddrPort                        // peer's SCION host IP:port
+	paths           map[scionPathKey]*scionPathProbeState // probed paths (up to scionMaxProbePaths)
+	activePath      scionPathKey                          // currently selected best path for data
+	lastDiscoveryAt time.Time                             // when path discovery last started (throttle)
+	lastFullEvalAt  mono.Time                             // throttles re-evaluation of SCION path latencies
+	probeRoundRobin int                                   // round-robin index for non-best path probing
+}
+
+// scionPathProbeState tracks disco probing state for one SCION path.
+type scionPathProbeState struct {
+	fingerprint     snet.PathFingerprint
+	displayStr      string // cached from scionPathInfo.displayStr for lock-safe logging
+	lastPing        mono.Time
+	recentPongs     [scionPongHistoryCount]scionPongReply // ring buffer
+	recentPong      uint16                                // index of most recent entry
+	pongCount       uint16                                // total pongs received (capped at ring size)
+	pingsSent       uint32                                // total pings sent on this path
+	pongsReceived   uint32                                // total pongs received (uncapped)
+	consecutiveLoss uint16                                // consecutive pings without pong (reset on pong)
+	healthy         bool                                  // false = demoted from active selection
+}
+
+// scionPongReply records one pong measurement for a SCION path.
+type scionPongReply struct {
+	latency time.Duration
+	pongAt  mono.Time
+}
+
+// addPongReply records a pong measurement in the ring buffer.
+func (ps *scionPathProbeState) addPongReply(r scionPongReply) {
+	ps.recentPong = (ps.recentPong + 1) % scionPongHistoryCount
+	ps.recentPongs[ps.recentPong] = r
+	if ps.pongCount < scionPongHistoryCount {
+		ps.pongCount++
+	}
+}
+
+// latency returns the median pong latency from available measurements,
+// or time.Hour if no pongs received. The median is robust to single-sample
+// outliers and provides stable path comparison for anti-flap logic.
+func (ps *scionPathProbeState) latency() time.Duration {
+	if ps.pongCount == 0 {
+		return time.Hour
+	}
+	n := int(ps.pongCount)
+	if n == 1 {
+		return ps.recentPongs[ps.recentPong].latency
+	}
+	samples := make([]time.Duration, n)
+	for i := range n {
+		idx := (int(ps.recentPong) - i + scionPongHistoryCount) % scionPongHistoryCount
+		samples[i] = ps.recentPongs[idx].latency
+	}
+	slices.Sort(samples)
+	return samples[n/2]
+}
+
+// scionFastPath holds a pre-serialized SCION+UDP header template for a
+// specific path. At send time, the template is copied, per-packet fields
+// (PayloadLen, UDP Length, UDP Checksum) are patched, payload is appended,
+// and the result is sent directly on the underlay UDP socket — bypassing
+// snet.Conn and gopacket serialization entirely.
+type scionFastPath struct {
+	hdr        []byte       // [SCION header][UDP header], no payload
+	udpOffset  int          // byte offset of UDP header within hdr
+	nextHop    *net.UDPAddr // underlay next-hop for this path
+	pseudoCsum uint32       // constant part of SCION pseudo-header checksum
+}
+
+// scionMaxBatchSize is the max number of packets in a single sendmmsg call.
+const scionMaxBatchSize = 64
+
+// scionSendBatch is a reusable set of buffers for sendSCIONBatchFast.
+type scionSendBatch struct {
+	bufs [][]byte
+	msgs []ipv4.Message
+}
+
+var scionSendBatchPool = sync.Pool{
+	New: func() any {
+		b := &scionSendBatch{
+			bufs: make([][]byte, scionMaxBatchSize),
+			msgs: make([]ipv4.Message, scionMaxBatchSize),
+		}
+		for i := range b.bufs {
+			b.bufs[i] = make([]byte, 1500)
+		}
+		for i := range b.msgs {
+			b.msgs[i].Buffers = make([][]byte, 1)
+		}
+		return b
+	},
+}
+
+// scionRecvBatch is a reusable set of buffers for receiveSCIONBatch.
+type scionRecvBatch struct {
+	msgs []ipv4.Message
+	bufs [][]byte
+	scn  slayers.SCION // reusable SCION header parser (with RecyclePaths)
+}
+
+var scionRecvBatchPool = sync.Pool{
+	New: func() any {
+		b := &scionRecvBatch{
+			msgs: make([]ipv4.Message, scionMaxBatchSize),
+			bufs: make([][]byte, scionMaxBatchSize),
+		}
+		b.scn.RecyclePaths()
+		for i := range b.bufs {
+			b.bufs[i] = make([]byte, 1500)
+		}
+		for i := range b.msgs {
+			b.msgs[i].Buffers = [][]byte{b.bufs[i]}
+		}
+		return b
+	},
+}
+
+// putScionRecvBatch resets batch state and returns it to the pool.
+func putScionRecvBatch(batch *scionRecvBatch) {
+	for i := range batch.msgs {
+		batch.msgs[i].N = 0
+		batch.msgs[i].Addr = nil
+		batch.msgs[i].Buffers[0] = batch.bufs[i]
+	}
+	scionRecvBatchPool.Put(batch)
+}
+
+// scionPseudoHeaderPartial computes the constant part of the SCION
+// pseudo-header checksum: srcIA + dstIA + srcAddr + dstAddr + protocol(17).
+// The per-packet upper-layer length and data are added at send time.
+func scionPseudoHeaderPartial(srcIA, dstIA addr.IA, srcIP, dstIP netip.Addr) uint32 {
+	var csum uint32
+	var buf [8]byte
+
+	// Source IA (8 bytes)
+	binary.BigEndian.PutUint64(buf[:], uint64(srcIA))
+	for i := 0; i < 8; i += 2 {
+		csum += uint32(buf[i]) << 8
+		csum += uint32(buf[i+1])
+	}
+
+	// Destination IA (8 bytes)
+	binary.BigEndian.PutUint64(buf[:], uint64(dstIA))
+	for i := 0; i < 8; i += 2 {
+		csum += uint32(buf[i]) << 8
+		csum += uint32(buf[i+1])
+	}
+
+	// Source address
+	if srcIP.Is4() {
+		b4 := srcIP.As4()
+		csum += uint32(b4[0])<<8 + uint32(b4[1])
+		csum += uint32(b4[2])<<8 + uint32(b4[3])
+	} else {
+		b16 := srcIP.As16()
+		for i := 0; i < 16; i += 2 {
+			csum += uint32(b16[i])<<8 + uint32(b16[i+1])
+		}
+	}
+
+	// Destination address
+	if dstIP.Is4() {
+		b4 := dstIP.As4()
+		csum += uint32(b4[0])<<8 + uint32(b4[1])
+		csum += uint32(b4[2])<<8 + uint32(b4[3])
+	} else {
+		b16 := dstIP.As16()
+		for i := 0; i < 16; i += 2 {
+			csum += uint32(b16[i])<<8 + uint32(b16[i+1])
+		}
+	}
+
+	// Protocol: L4UDP = 17
+	csum += 17
+
+	return csum
+}
+
+// scionFinishChecksum completes the SCION/UDP checksum by adding the
+// upper-layer length and bytes to the pre-computed partial checksum,
+// then folding and complementing.
+func scionFinishChecksum(partialCsum uint32, upperLayer []byte) uint16 {
+	csum := partialCsum
+
+	// Add upper-layer length
+	l := uint32(len(upperLayer))
+	csum += (l >> 16) + (l & 0xffff)
+
+	// Sum upper-layer bytes in 16-bit words
+	n := len(upperLayer)
+	for i := 0; i+1 < n; i += 2 {
+		csum += uint32(upperLayer[i]) << 8
+		csum += uint32(upperLayer[i+1])
+	}
+	if n%2 == 1 {
+		csum += uint32(upperLayer[n-1]) << 8
+	}
+
+	// Fold to 16 bits
+	for csum > 0xffff {
+		csum = (csum >> 16) + (csum & 0xffff)
+	}
+	return ^uint16(csum)
+}
+
+// buildSCIONFastPath creates a pre-serialized header template for fast-path
+// sends. Must be called with pi.mu held (or before pi is shared).
+// Returns nil if the fast path cannot be built (e.g. no discovered path).
+func buildSCIONFastPath(sc *scionConn, pi *scionPathInfo) *scionFastPath {
+	if sc.underlayConn == nil {
+		return nil
+	}
+	dst := pi.cachedDst
+	if dst == nil || dst.Path == nil || dst.NextHop == nil {
+		return nil
+	}
+
+	dstIP, ok := netip.AddrFromSlice(dst.Host.IP)
+	if !ok {
+		return nil
+	}
+	srcIP := sc.localHostIP
+
+	// Use snet.Packet.Serialize() with empty payload to get a correctly
+	// encoded SCION+UDP header template.
+	pkt := &snet.Packet{
+		PacketInfo: snet.PacketInfo{
+			Destination: snet.SCIONAddress{IA: pi.peerIA, Host: addr.HostIP(dstIP)},
+			Source:      snet.SCIONAddress{IA: sc.localIA, Host: addr.HostIP(srcIP)},
+			Path:        dst.Path,
+			Payload: snet.UDPPayload{
+				SrcPort: sc.localPort,
+				DstPort: uint16(dst.Host.Port),
+				Payload: nil, // empty payload → headers only
+			},
+		},
+	}
+	if err := pkt.Serialize(); err != nil {
+		return nil
+	}
+
+	// pkt.Bytes is now [SCION header][8-byte UDP header]
+	hdr := make([]byte, len(pkt.Bytes))
+	copy(hdr, pkt.Bytes)
+	udpOffset := len(hdr) - 8
+
+	pseudoCsum := scionPseudoHeaderPartial(sc.localIA, pi.peerIA, srcIP, dstIP)
+
+	return &scionFastPath{
+		hdr:        hdr,
+		udpOffset:  udpOffset,
+		nextHop:    dst.NextHop,
+		pseudoCsum: pseudoCsum,
+	}
+}
+
+// parseSCIONPacket parses a raw SCION packet from the underlay, extracting
+// the source address info and UDP payload. scn is a reusable slayers.SCION
+// (with RecyclePaths enabled). Returns srcIA, srcAddr, payload, rawPath, ok.
+func parseSCIONPacket(data []byte, scn *slayers.SCION) (
+	srcIA addr.IA, srcAddr netip.AddrPort, payload []byte, rawPathBytes []byte, ok bool,
+) {
+	if err := scn.DecodeFromBytes(data, gopacket.NilDecodeFeedback); err != nil {
+		return 0, netip.AddrPort{}, nil, nil, false
+	}
+	if scn.NextHdr != slayers.L4UDP {
+		return 0, netip.AddrPort{}, nil, nil, false
+	}
+
+	srcHost, err := scn.SrcAddr()
+	if err != nil {
+		return 0, netip.AddrPort{}, nil, nil, false
+	}
+	srcIP := srcHost.IP()
+	srcIA = scn.SrcIA
+
+	// L4 payload starts at HdrLen * 4 bytes (SCION header is HdrLen
+	// 4-byte words). The first 8 bytes are the UDP header.
+	hdrBytes := int(scn.HdrLen) * 4
+	if len(data) < hdrBytes+8 {
+		return 0, netip.AddrPort{}, nil, nil, false
+	}
+	// Extract UDP source port from the first 2 bytes of the L4 header.
+	srcPort := binary.BigEndian.Uint16(data[hdrBytes:])
+	srcAddr = netip.AddrPortFrom(srcIP, srcPort)
+	payload = data[hdrBytes+8:]
+
+	// Extract raw path bytes for potential reversal (disco first-contact).
+	if scn.Path != nil {
+		pathLen := scn.Path.Len()
+		// The path sits between the address header and the L4 header
+		// in the SCION common+address+path header region.
+		addrHdrLen := scn.AddrHdrLen()
+		// Common header is 12 bytes, then address header, then path.
+		pathStart := 12 + addrHdrLen
+		pathEnd := pathStart + pathLen
+		if pathEnd <= hdrBytes && pathLen > 0 {
+			rawPathBytes = data[pathStart:pathEnd]
+		}
+	}
+
+	return srcIA, srcAddr, payload, rawPathBytes, true
+}
+
+// buildSCIONReplyAddr builds an *snet.UDPAddr with reversed path for disco
+// reply routing from raw path bytes extracted during receive. nextHop is the
+// underlay border router address from the incoming packet (msg.Addr from
+// recvmmsg); it is required for the reply to be routable.
+func buildSCIONReplyAddr(srcIA addr.IA, srcHostAddr netip.AddrPort, rawPathBytes []byte, nextHop *net.UDPAddr) *snet.UDPAddr {
+	if len(rawPathBytes) == 0 {
+		return nil
+	}
+	// Copy path bytes since DecodeFromBytes references the slice.
+	pathCopy := make([]byte, len(rawPathBytes))
+	copy(pathCopy, rawPathBytes)
+
+	var raw scionpath.Raw
+	if err := raw.DecodeFromBytes(pathCopy); err != nil {
+		return nil
+	}
+	reversed, err := raw.Reverse()
+	if err != nil {
+		return nil
+	}
+	// Serialize the reversed path to raw bytes and wrap in snetpath.SCION
+	// which implements snet.DataplanePath.
+	revBytes := make([]byte, reversed.Len())
+	if err := reversed.SerializeTo(revBytes); err != nil {
+		return nil
+	}
+
+	return &snet.UDPAddr{
+		IA: srcIA,
+		Host: &net.UDPAddr{
+			IP:   srcHostAddr.Addr().AsSlice(),
+			Port: int(srcHostAddr.Port()),
+		},
+		Path:    snetpath.SCION{Raw: revBytes},
+		NextHop: nextHop,
+	}
+}
+
+// scionBatchRW abstracts ipv4.PacketConn and ipv6.PacketConn for
+// batch I/O. Both have identical ReadBatch/WriteBatch signatures
+// since ipv4.Message and ipv6.Message are the same type (socket.Message).
+// On non-Linux platforms, ReadBatch/WriteBatch fall back to per-message
+// sendto/recvfrom (golang.org/x/net handles this internally).
+type scionBatchRW interface {
+	ReadBatch([]ipv4.Message, int) (int, error)
+	WriteBatch([]ipv4.Message, int) (int, error)
+}
+
+// scionConn wraps a SCION connection for use by magicsock.
+type scionConn struct {
+	conn         *snet.Conn       // from SCIONNetwork.Listen()
+	underlayConn *net.UDPConn     // raw underlay for fast-path sends (owned by conn)
+	underlayXPC  scionBatchRW     // for WriteBatch / sendmmsg (ipv4 or ipv6)
+	localIA      addr.IA          // our ISD-AS
+	localHostIP  netip.Addr       // local host IP (e.g. 127.0.0.1)
+	localPort    uint16           // local SCION/UDP port
+	daemon       daemon.Connector // for path queries
+	topo         snet.Topology    // local topology
+	shimConn     *net.UDPConn     // receive-only socket on port 30041; nil if unavailable
+	shimXPC      scionBatchRW     // batch reader for shim socket
+}
+
+// close shuts down the SCION connection and daemon connector.
+func (sc *scionConn) close() error {
+	if sc.shimConn != nil {
+		sc.shimConn.Close()
+	}
+	if sc.conn != nil {
+		sc.conn.Close()
+	}
+	if sc.daemon != nil {
+		sc.daemon.Close()
+	}
+	return nil
+}
+
+// closeSocket closes only the SCION socket (conn, underlayConn, underlayXPC)
+// and the dispatcher shim, preserving the daemon connector and topology for
+// socket-only reconnection.
+func (sc *scionConn) closeSocket() {
+	if sc.shimConn != nil {
+		sc.shimConn.Close()
+	}
+	sc.shimConn = nil
+	sc.shimXPC = nil
+	if sc.conn != nil {
+		sc.conn.Close()
+	}
+	sc.conn = nil
+	sc.underlayConn = nil
+	sc.underlayXPC = nil
+}
+
+// writeTo sends b to a peer identified by the given scionPathInfo.
+func (sc *scionConn) writeTo(b []byte, pi *scionPathInfo) (int, error) {
+	pi.mu.Lock()
+	replyPath := pi.replyPath
+	cachedDst := pi.cachedDst
+	pi.mu.Unlock()
+
+	dst := cachedDst
+	if dst == nil && replyPath != nil {
+		dst = replyPath
+	}
+	if dst == nil {
+		return 0, fmt.Errorf("no SCION destination")
+	}
+	return sc.conn.WriteTo(b, dst)
+}
+
+// readFrom reads a packet from the SCION connection, returning the data, the
+// source SCION address, and any error.
+func (sc *scionConn) readFrom(b []byte) (int, *snet.UDPAddr, error) {
+	n, srcAddr, err := sc.conn.ReadFrom(b)
+	if err != nil {
+		return 0, nil, err
+	}
+	src, ok := srcAddr.(*snet.UDPAddr)
+	if !ok {
+		return 0, nil, fmt.Errorf("unexpected source address type: %T", srcAddr)
+	}
+	return n, src, nil
+}
+
+// scionDaemonAddr returns the SCION daemon address to use, checking the
+// environment variable first, then falling back to the default socket.
+func scionDaemonAddr() string {
+	if a := scionDaemonAddress(); a != "" {
+		return a
+	}
+	return daemon.DefaultAPIAddress
+}
+
+// scionListenPort returns the SCION port to use, checking the TS_SCION_PORT
+// environment variable first, then falling back to 0 (auto-select from the
+// topology's dispatched port range).
+func scionListenPort() uint16 {
+	if p := scionPort(); p != "" {
+		var v int
+		if _, err := fmt.Sscanf(p, "%d", &v); err == nil && v > 0 && v <= 65535 {
+			return uint16(v)
+		}
+	}
+	return 0 // let snet auto-select from topology port range
+}
+
+// scionResolveLocalIP determines the local IP for the SCION underlay socket
+// by checking what source IP the OS would use to reach the border routers'
+// internal addresses from the topology. This mirrors how `scion address` works
+// (via addrutil.ResolveLocal).
+//
+// With multiple BRs, if all resolve to the same local IP, that IP is used.
+// If they disagree, the first resolved IP is used and a warning is logged —
+// the user should set TS_SCION_LISTEN_ADDR explicitly.
+//
+// Falls back to 127.0.0.1 if no interfaces or resolution fails.
+func scionResolveLocalIP(ctx context.Context, connector daemon.Connector, logf logger.Logf) netip.Addr {
+	ifMap, err := connector.Interfaces(ctx)
+	if err != nil || len(ifMap) == 0 {
+		return netip.AddrFrom4([4]byte{127, 0, 0, 1})
+	}
+
+	var first netip.Addr
+	allSame := true
+	for _, ap := range ifMap {
+		resolved, err := addrutil.ResolveLocal(ap.Addr().AsSlice())
+		if err != nil {
+			continue
+		}
+		ip, ok := netip.AddrFromSlice(resolved)
+		if !ok {
+			continue
+		}
+		ip = ip.Unmap()
+		if !first.IsValid() {
+			first = ip
+		} else if first != ip {
+			allSame = false
+		}
+	}
+
+	if !first.IsValid() {
+		return netip.AddrFrom4([4]byte{127, 0, 0, 1})
+	}
+	if !allSame {
+		logf("magicsock: SCION: multiple BRs resolve to different local IPs; using %s, set TS_SCION_LISTEN_ADDR to override", first)
+	}
+	return first
+}
+
+// scionListenAddr returns the listen address for the SCION underlay socket.
+// TS_SCION_LISTEN_ADDR can override the IP (e.g. "::1" for IPv6 localhost).
+// Otherwise resolves the local IP from the topology's BR internal addresses.
+func scionListenAddr(ctx context.Context, connector daemon.Connector, logf logger.Logf) *net.UDPAddr {
+	port := scionListenPort()
+	if a := scionListenAddrEnv(); a != "" {
+		ip := net.ParseIP(a)
+		if ip != nil {
+			return &net.UDPAddr{IP: ip, Port: int(port)}
+		}
+	}
+	ip := scionResolveLocalIP(ctx, connector, logf)
+	return &net.UDPAddr{IP: ip.AsSlice(), Port: int(port)}
+}
+
+// forceEmbeddedSCION is the TS_SCION_EMBEDDED envknob. When set to "1",
+// the external daemon attempt is skipped and only the embedded connector is tried.
+var forceEmbeddedSCION = envknob.RegisterBool("TS_SCION_EMBEDDED")
+
+// forceBootstrapSCION is the TS_SCION_FORCE_BOOTSTRAP envknob. When set to "1",
+// the local topology file attempt is skipped and only the bootstrap attempt is tried.
+var forceBootstrapSCION = envknob.RegisterBool("TS_SCION_FORCE_BOOTSTRAP")
+
+// trySCIONConnect attempts to set up a SCION connection using a cascading
+// fallback strategy:
+//  1. External daemon (existing behavior, quick check) — skipped if TS_SCION_EMBEDDED=1
+//  2. Embedded with existing local topology file (TS_SCION_TOPOLOGY or /etc/scion/topology.json)
+//  3. Bootstrap from configured URL (TS_SCION_BOOTSTRAP_URL / TS_SCION_BOOTSTRAP_URLS)
+//  4. DNS-based discovery (SRV for _sciondiscovery._tcp)
+//  5. Hardcoded bootstrap URLs (if any)
+//
+// Returns nil if SCION is not available via any method.
+func trySCIONConnect(ctx context.Context, logf logger.Logf, netMon *netmon.Monitor) (*scionConn, error) {
+	var externalErr error
+
+	// Step 1: Try external daemon (unless forced embedded).
+	if !forceEmbeddedSCION() {
+		sc, err := tryExternalDaemon(ctx, logf, netMon)
+		if err == nil {
+			return sc, nil
+		}
+		externalErr = err
+	}
+
+	// Step 2: Try embedded with existing local topology file.
+	if !forceBootstrapSCION() {
+		topoPath := scionTopologyPath()
+		if _, err := os.Stat(topoPath); err == nil {
+			sc, err := tryEmbeddedDaemon(ctx, topoPath, logf, netMon)
+			if err == nil {
+				return sc, nil
+			}
+			// Fall through to bootstrap attempts.
+		}
+	}
+
+	// Steps 3-5: Try bootstrap from URLs (explicit, DNS-discovered, hardcoded).
+	stateDir := scionStateDir()
+	if stateDir == "" {
+		if externalErr != nil {
+			return nil, fmt.Errorf("external daemon: %w; embedded: no state directory available", externalErr)
+		}
+		return nil, fmt.Errorf("SCION not available: no external daemon, no topology file, no state directory for bootstrap")
+	}
+	for _, url := range bootstrapURLs(ctx, logf) {
+		if err := bootstrapSCION(ctx, logf, url, stateDir); err != nil {
+			logf("scion: bootstrap from %s failed: %v", url, err)
+			continue
+		}
+		bootstrappedTopo := filepath.Join(stateDir, "topology.json")
+		if _, err := os.Stat(bootstrappedTopo); err != nil {
+			continue
+		}
+		sc, err := tryEmbeddedDaemon(ctx, bootstrappedTopo, logf, netMon)
+		if err == nil {
+			return sc, nil
+		}
+	}
+
+	if externalErr != nil {
+		return nil, fmt.Errorf("external daemon: %w; embedded: no topology available", externalErr)
+	}
+	return nil, fmt.Errorf("SCION not available: no external daemon, no topology file, no bootstrap server")
+}
+
+// tryExternalDaemon attempts to connect to an external SCION daemon and set up
+// a SCION listener. This is the original trySCIONConnect behavior.
+func tryExternalDaemon(ctx context.Context, logf logger.Logf, netMon *netmon.Monitor) (*scionConn, error) {
+	daemonAddr := scionDaemonAddr()
+	svc := daemon.Service{Address: daemonAddr}
+	conn, err := svc.Connect(ctx)
+	if err != nil {
+		return nil, fmt.Errorf("connecting to SCION daemon at %s: %w", daemonAddr, err)
+	}
+
+	topo, err := snetTopologyFromConnector(ctx, conn)
+	if err != nil {
+		conn.Close()
+		return nil, fmt.Errorf("building topology from daemon: %w", err)
+	}
+
+	// Probe Paths() to detect wire-format incompatibility with older
+	// daemons (e.g. v0.12 daemon vs v0.14 client). Simple RPCs like
+	// LocalIA/Interfaces/ASInfo use compatible proto types, but Paths
+	// responses with real hop data trigger unmarshal failures.
+	// We need a reachable remote IA to get a non-empty response;
+	// parse the topology file for a neighbor AS.
+	if neighborIA, ok := neighborIAFromTopology(scionTopologyPath()); ok {
+		localIA, _ := conn.LocalIA(ctx)
+		if _, err := conn.Paths(ctx, neighborIA, localIA, daemon.PathReqFlags{}); err != nil {
+			conn.Close()
+			return nil, fmt.Errorf("daemon path probe failed (version mismatch?): %w", err)
+		}
+	}
+
+	sc, err := finishSCIONConnect(ctx, conn, topo, logf, netMon)
+	if err != nil {
+		conn.Close()
+		return nil, err
+	}
+	return sc, nil
+}
+
+// snetTopologyFromConnector builds an snet.Topology struct by querying
+// a daemon.Connector for local topology information.
+func snetTopologyFromConnector(ctx context.Context, conn daemon.Connector) (snet.Topology, error) {
+	localIA, err := conn.LocalIA(ctx)
+	if err != nil {
+		return snet.Topology{}, fmt.Errorf("querying local IA: %w", err)
+	}
+	portStart, portEnd, err := conn.PortRange(ctx)
+	if err != nil {
+		return snet.Topology{}, fmt.Errorf("querying port range: %w", err)
+	}
+	ifMap, err := conn.Interfaces(ctx)
+	if err != nil {
+		return snet.Topology{}, fmt.Errorf("querying interfaces: %w", err)
+	}
+	return snet.Topology{
+		LocalIA:   localIA,
+		PortRange: snet.TopologyPortRange{Start: portStart, End: portEnd},
+		Interface: func(id uint16) (netip.AddrPort, bool) {
+			ap, ok := ifMap[id]
+			return ap, ok
+		},
+	}, nil
+}
+
+// neighborIAFromTopology parses the SCION topology JSON file and returns
+// the IA of the first neighbor AS found in the border router interfaces.
+// This is used to probe the daemon with a Paths() call that returns real
+// path data, detecting proto wire-format incompatibilities.
+func neighborIAFromTopology(topoPath string) (addr.IA, bool) {
+	data, err := os.ReadFile(topoPath)
+	if err != nil {
+		return 0, false
+	}
+	var topo struct {
+		BorderRouters map[string]struct {
+			Interfaces map[string]struct {
+				ISDAS string `json:"isd_as"`
+			} `json:"interfaces"`
+		} `json:"border_routers"`
+	}
+	if err := json.Unmarshal(data, &topo); err != nil {
+		return 0, false
+	}
+	for _, br := range topo.BorderRouters {
+		for _, iface := range br.Interfaces {
+			ia, err := addr.ParseIA(iface.ISDAS)
+			if err == nil {
+				return ia, true
+			}
+		}
+	}
+	return 0, false
+}
+
+// finishSCIONConnect completes the SCION connection setup given a
+// daemon.Connector (for path queries) and snet.Topology (for local info).
+// This is shared between the external daemon and embedded connector paths.
+func finishSCIONConnect(ctx context.Context, connector daemon.Connector, topo snet.Topology, logf logger.Logf, netMon *netmon.Monitor) (*scionConn, error) {
+	localIA, err := connector.LocalIA(ctx)
+	if err != nil {
+		return nil, fmt.Errorf("querying local IA: %w", err)
+	}
+
+	network := &snet.SCIONNetwork{
+		Topology: topo,
+	}
+
+	listenAddr := scionListenAddr(ctx, connector, logf)
+	if listenAddr.Port != 0 {
+		// Validate the configured port against the dispatched range.
+		portMin, portMax, err := connector.PortRange(ctx)
+		if err != nil {
+			return nil, fmt.Errorf("querying SCION port range: %w", err)
+		}
+		listenPort := uint16(listenAddr.Port)
+		if listenPort < portMin || listenPort > portMax {
+			return nil, fmt.Errorf("TS_SCION_PORT=%d outside dispatched range [%d, %d]", listenPort, portMin, portMax)
+		}
+	}
+
+	// Use OpenRaw + NewCookedConn instead of Listen so we can set socket
+	// buffer sizes on the underlying UDP connection before wrapping it.
+	pconn, err := network.OpenRaw(ctx, listenAddr)
+	if err != nil {
+		return nil, fmt.Errorf("listening on SCION %s: %w", listenAddr, err)
+	}
+
+	// Extract the underlay *net.UDPConn for fast-path sends that bypass
+	// snet.Conn serialization. Also increase socket buffer sizes.
+	var underlayConn *net.UDPConn
+	if pc, ok := pconn.(*snet.SCIONPacketConn); ok {
+		underlayConn = pc.Conn
+		logf("magicsock: SCION: extracted underlay conn, local=%v", underlayConn.LocalAddr())
+		if err := pc.SetReadBuffer(socketBufferSize); err != nil {
+			logf("magicsock: SCION: failed to set read buffer to %d: %v", socketBufferSize, err)
+		}
+		if err := pc.SetWriteBuffer(socketBufferSize); err != nil {
+			logf("magicsock: SCION: failed to set write buffer to %d: %v", socketBufferSize, err)
+		}
+	} else {
+		logf("magicsock: SCION: WARNING: pconn is %T, not *snet.SCIONPacketConn; cannot extract underlay", pconn)
+	}
+
+	// Apply platform-specific socket options (SO_MARK on Linux,
+	// VpnService.protect on Android, IP_BOUND_IF on macOS) to
+	// prevent the SCION underlay socket from routing through the
+	// VPN tunnel, which would cause loops.
+	if underlayConn != nil {
+		rawConn, err := underlayConn.SyscallConn()
+		if err == nil {
+			lc := netns.Listener(logf, netMon)
+			if lc.Control != nil {
+				logf("magicsock: SCION: calling netns control (VpnService.protect) on underlay fd")
+				if err := lc.Control("udp", underlayConn.LocalAddr().String(), rawConn); err != nil {
+					logf("magicsock: SCION: netns control FAILED: %v", err)
+				} else {
+					logf("magicsock: SCION: netns control succeeded on underlay socket")
+				}
+			} else {
+				logf("magicsock: SCION: WARNING: netns Listener.Control is nil, socket NOT protected")
+			}
+		} else {
+			logf("magicsock: SCION: SyscallConn: %v", err)
+		}
+	} else {
+		logf("magicsock: SCION: WARNING: no underlay conn, socket NOT protected from VPN")
+	}
+
+	sconn, err := snet.NewCookedConn(pconn, topo)
+	if err != nil {
+		pconn.Close()
+		return nil, fmt.Errorf("creating SCION conn: %w", err)
+	}
+
+	// Extract local address info for fast-path header templates.
+	var localHostIP netip.Addr
+	var localPort uint16
+	if sa, saOk := sconn.LocalAddr().(*snet.UDPAddr); saOk && sa.Host != nil {
+		if ip, ipOk := netip.AddrFromSlice(sa.Host.IP); ipOk {
+			localHostIP = ip
+		}
+		localPort = uint16(sa.Host.Port)
+	}
+
+	// Wrap underlay conn for sendmmsg batching, selecting the correct
+	// address family based on the local address.
+	var underlayXPC scionBatchRW
+	if underlayConn != nil {
+		local, ok := underlayConn.LocalAddr().(*net.UDPAddr)
+		if !ok {
+			return nil, fmt.Errorf("unexpected underlay local address type %T", underlayConn.LocalAddr())
+		}
+		if local.IP.To4() != nil {
+			underlayXPC = ipv4.NewPacketConn(underlayConn)
+		} else {
+			underlayXPC = ipv6.NewPacketConn(underlayConn)
+		}
+	}
+
+	sc := &scionConn{
+		conn:         sconn,
+		underlayConn: underlayConn,
+		underlayXPC:  underlayXPC,
+		localIA:      localIA,
+		localHostIP:  localHostIP,
+		localPort:    localPort,
+		daemon:       connector,
+		topo:         topo,
+	}
+	openDispatcherShim(sc, logf, netMon)
+	return sc, nil
+}
+
+// openDispatcherShim tries to bind a receive-only UDP socket on the legacy
+// dispatcher port (30041). In older SCION deployments, border routers send all
+// packets to this port instead of directly to the application's endhost port.
+// If binding succeeds (no dispatcher running), the shim socket receives packets
+// identically to the main socket. If binding fails (EADDRINUSE), we log and
+// continue — the real dispatcher handles forwarding.
+func openDispatcherShim(sc *scionConn, logf logger.Logf, netMon *netmon.Monitor) {
+	if noDispatcherShim() {
+		logf("magicsock: SCION dispatcher shim disabled via TS_SCION_NO_DISPATCHER_SHIM")
+		return
+	}
+	if sc.localPort == scionDispatcherPort {
+		logf("magicsock: SCION main socket already on dispatcher port %d, skipping shim", scionDispatcherPort)
+		return
+	}
+
+	shimAddr := &net.UDPAddr{
+		IP:   sc.localHostIP.AsSlice(),
+		Port: scionDispatcherPort,
+	}
+	shimConn, err := net.ListenUDP("udp", shimAddr)
+	if err != nil {
+		logf("magicsock: SCION dispatcher shim on :%d: %v (continuing without shim)", scionDispatcherPort, err)
+		return
+	}
+
+	if err := shimConn.SetReadBuffer(socketBufferSize); err != nil {
+		logf("magicsock: SCION shim: failed to set read buffer to %d: %v", socketBufferSize, err)
+	}
+
+	// Apply platform-specific socket options (SO_MARK, VPN isolation)
+	// to prevent the shim socket from routing through the VPN tunnel.
+	if netMon != nil {
+		rawConn, err := shimConn.SyscallConn()
+		if err == nil {
+			lc := netns.Listener(logf, netMon)
+			if lc.Control != nil {
+				if err := lc.Control("udp", shimConn.LocalAddr().String(), rawConn); err != nil {
+					logf("magicsock: SCION shim: netns control: %v", err)
+				}
+			}
+		} else {
+			logf("magicsock: SCION shim: SyscallConn: %v", err)
+		}
+	}
+
+	// Wrap for batch I/O, selecting address family based on local address.
+	var xpc scionBatchRW
+	local, ok := shimConn.LocalAddr().(*net.UDPAddr)
+	if !ok {
+		shimConn.Close()
+		logf("magicsock: SCION shim: unexpected local address type %T", shimConn.LocalAddr())
+		return
+	}
+	if local.IP.To4() != nil {
+		xpc = ipv4.NewPacketConn(shimConn)
+	} else {
+		xpc = ipv6.NewPacketConn(shimConn)
+	}
+
+	sc.shimConn = shimConn
+	sc.shimXPC = xpc
+	logf("magicsock: SCION dispatcher shim listening on %s", shimConn.LocalAddr())
+}
+
+// parseSCIONServiceAddr parses a SCION service description string of the form
+// "ISD-AS,[host-IP]" and returns the IA and host address. The port comes from
+// the Service.Port field. Accepts both bracketed ("[192.0.2.1]", "[2001:db8::1]")
+// and unbracketed ("192.0.2.1", "2001:db8::1") IP formats for backward compatibility.
+func parseSCIONServiceAddr(description string, port uint16) (ia addr.IA, hostAddr netip.AddrPort, err error) {
+	parts := strings.SplitN(description, ",", 2)
+	if len(parts) != 2 {
+		return 0, netip.AddrPort{}, fmt.Errorf("invalid SCION service description %q: want ISD-AS,[host-IP]", description)
+	}
+
+	ia, err = addr.ParseIA(parts[0])
+	if err != nil {
+		return 0, netip.AddrPort{}, fmt.Errorf("parsing SCION IA %q: %w", parts[0], err)
+	}
+
+	// Strip brackets if present (e.g., "[192.0.2.1]" or "[2001:db8::1]").
+	ipStr := strings.TrimPrefix(strings.TrimSuffix(parts[1], "]"), "[")
+	hostIP, err := netip.ParseAddr(ipStr)
+	if err != nil {
+		return 0, netip.AddrPort{}, fmt.Errorf("parsing SCION host IP %q: %w", parts[1], err)
+	}
+
+	return ia, netip.AddrPortFrom(hostIP, port), nil
+}
+
+// sendSCIONBatch sends a batch of WireGuard packets over the SCION connection.
+// It looks up the full path info from the Conn's scionPaths registry using the
+// scionPathKey from the epAddr.
+//
+// When a fast-path template is available (pre-serialized headers + underlay
+// socket), packets are serialized by patching a header template and sent via
+// sendmmsg in a single syscall. Otherwise, falls back to snet.Conn.WriteTo
+// per packet.
+func (c *Conn) sendSCIONBatch(addr epAddr, buffs [][]byte, offset int) (sent bool, err error) {
+	sc := c.pconnSCION.Load()
+	if sc == nil {
+		return false, errNoSCION
+	}
+
+	pi := c.lookupSCIONPathLocking(addr.scionKey)
+	if pi == nil {
+		return false, fmt.Errorf("no SCION path info for key %d", addr.scionKey)
+	}
+
+	// Read path info once for the entire batch to avoid repeated locking.
+	pi.mu.Lock()
+	replyPath := pi.replyPath
+	cachedDst := pi.cachedDst
+	fastPath := pi.fastPath
+	expired := !pi.expiry.IsZero() && time.Now().After(pi.expiry)
+	pi.mu.Unlock()
+	if expired {
+		return false, fmt.Errorf("SCION path expired for key %d", addr.scionKey)
+	}
+
+	// Fast path: pre-serialized headers + sendmmsg.
+	if fastPath != nil && sc.underlayXPC != nil && !scionNoFastPath() {
+		err = c.sendSCIONBatchFast(sc, fastPath, buffs, offset)
+		if err != nil {
+			c.handleSCIONSendError(err)
+		}
+		return err == nil, err
+	}
+
+	// Slow path: snet.Conn.WriteTo per packet.
+	dst := cachedDst
+	if dst == nil && replyPath != nil {
+		dst = replyPath
+	}
+	if dst == nil {
+		return false, fmt.Errorf("no SCION destination for key %d", addr.scionKey)
+	}
+
+	for _, buf := range buffs {
+		_, err = sc.conn.WriteTo(buf[offset:], dst)
+		if err != nil {
+			c.handleSCIONSendError(err)
+			return false, err
+		}
+	}
+	return true, nil
+}
+
+// sendSCIONBatchFast sends a batch of packets using pre-serialized SCION
+// headers and sendmmsg on the underlay UDP socket. Each packet is built by
+// copying the header template, patching per-packet fields (PayloadLen, UDP
+// Length, UDP Checksum), and appending the WireGuard payload.
+func (c *Conn) sendSCIONBatchFast(sc *scionConn, fp *scionFastPath, buffs [][]byte, offset int) error {
+	batch := scionSendBatchPool.Get().(*scionSendBatch)
+	defer scionSendBatchPool.Put(batch)
+
+	hdrLen := len(fp.hdr)
+	n := len(buffs)
+	if n > scionMaxBatchSize {
+		n = scionMaxBatchSize
+	}
+
+	for i := 0; i < n; i++ {
+		payload := buffs[i][offset:]
+		pktLen := hdrLen + len(payload)
+
+		// Grow buffer if needed.
+		buf := batch.bufs[i]
+		if cap(buf) < pktLen {
+			buf = make([]byte, pktLen)
+			batch.bufs[i] = buf
+		} else {
+			buf = buf[:pktLen]
+		}
+
+		// Copy header template and append payload.
+		copy(buf, fp.hdr)
+		copy(buf[hdrLen:], payload)
+
+		// Patch SCION PayloadLen (bytes 6:8) = UDP header (8) + payload.
+		udpTotalLen := uint16(8 + len(payload))
+		binary.BigEndian.PutUint16(buf[6:], udpTotalLen)
+
+		// Patch UDP Length (udpOffset+4:+6).
+		binary.BigEndian.PutUint16(buf[fp.udpOffset+4:], udpTotalLen)
+
+		// Zero checksum, compute over full upper layer, set result.
+		buf[fp.udpOffset+6] = 0
+		buf[fp.udpOffset+7] = 0
+		upperLayer := buf[fp.udpOffset:pktLen]
+		csum := scionFinishChecksum(fp.pseudoCsum, upperLayer)
+		binary.BigEndian.PutUint16(buf[fp.udpOffset+6:], csum)
+
+		batch.msgs[i].Buffers[0] = buf[:pktLen]
+		batch.msgs[i].Addr = fp.nextHop
+	}
+
+	// WriteBatch uses sendmmsg on Linux for batched sends.
+	msgs := batch.msgs[:n]
+	var head int
+	for {
+		written, err := sc.underlayXPC.WriteBatch(msgs[head:], 0)
+		if err != nil {
+			return err
+		}
+		head += written
+		if head >= n {
+			return nil
+		}
+	}
+}
+
+// sendSCION sends a single packet over SCION, used for disco messages.
+func (c *Conn) sendSCION(sk scionPathKey, b []byte) (bool, error) {
+	sc := c.pconnSCION.Load()
+	if sc == nil {
+		return false, errNoSCION
+	}
+	pi := c.lookupSCIONPathLocking(sk)
+	if pi == nil {
+		return false, fmt.Errorf("no SCION path info for key %d", sk)
+	}
+	pi.mu.Lock()
+	expired := !pi.expiry.IsZero() && time.Now().After(pi.expiry)
+	pi.mu.Unlock()
+	if expired {
+		return false, fmt.Errorf("SCION path expired for key %d", sk)
+	}
+	_, err := sc.writeTo(b, pi)
+	if err != nil {
+		c.handleSCIONSendError(err)
+		return false, err
+	}
+	return true, nil
+}
+
+// handleSCIONSendError triggers SCION reconnection when a send fails with
+// a socket error. This is the primary reconnection mechanism — rather than
+// polling for liveness on the receive side, we reconnect when sends actually
+// fail. The receive loop picks up the new socket automatically because the
+// old socket's close unblocks its read with net.ErrClosed.
+func (c *Conn) handleSCIONSendError(err error) {
+	if err == nil {
+		return
+	}
+	// Don't reconnect for logical errors (nil path, expired path, no SCION).
+	if errors.Is(err, errNoSCION) {
+		return
+	}
+	c.logf("magicsock: SCION send failed: %v, triggering reconnect", err)
+	go c.reconnectSCION()
+}
+
+// lookupSCIONPath returns the scionPathInfo for the given key, or nil if not found.
+// c.mu must be held.
+func (c *Conn) lookupSCIONPath(k scionPathKey) *scionPathInfo {
+	return c.scionPaths[k]
+}
+
+// lookupSCIONPathLocking returns the scionPathInfo for the given key, acquiring c.mu.
+func (c *Conn) lookupSCIONPathLocking(k scionPathKey) *scionPathInfo {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	return c.scionPaths[k]
+}
+
+// registerSCIONPath stores a scionPathInfo and returns a key for it.
+// c.mu must be held.
+func (c *Conn) registerSCIONPath(pi *scionPathInfo) scionPathKey {
+	k := scionPathKey(c.scionPathSeq.Add(1))
+	if c.scionPaths == nil {
+		c.scionPaths = make(map[scionPathKey]*scionPathInfo)
+	}
+	c.scionPaths[k] = pi
+	// Don't unconditionally overwrite scionPathsByAddr here — with multi-path,
+	// multiple keys share the same (IA, hostAddr). The caller is responsible
+	// for setting the active path via setActiveSCIONPath.
+	return k
+}
+
+// registerSCIONPathLocking stores a scionPathInfo, acquiring c.mu, and returns
+// a key for it.
+func (c *Conn) registerSCIONPathLocking(pi *scionPathInfo) scionPathKey {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	return c.registerSCIONPath(pi)
+}
+
+// unregisterSCIONPath removes a SCION path entry and its peerMap entry.
+// c.mu must be held.
+func (c *Conn) unregisterSCIONPath(k scionPathKey) {
+	if pi, ok := c.scionPaths[k]; ok {
+		// Only remove reverse index if it points to this key.
+		ak := scionAddrKey{ia: pi.peerIA, addr: pi.hostAddr}
+		if c.scionPathsByAddr[ak] == k {
+			delete(c.scionPathsByAddr, ak)
+		}
+		// Remove stale peerMap entry for this scionKey.
+		scionEp := epAddr{ap: pi.hostAddr, scionKey: k}
+		if peerInf := c.peerMap.byEpAddr[scionEp]; peerInf != nil {
+			delete(peerInf.epAddrs, scionEp)
+			delete(c.peerMap.byEpAddr, scionEp)
+		}
+	}
+	delete(c.scionPaths, k)
+}
+
+// setActiveSCIONPath updates the reverse index to point to the given key.
+// c.mu must be held.
+func (c *Conn) setActiveSCIONPath(peerIA addr.IA, hostAddr netip.AddrPort, k scionPathKey) {
+	if c.scionPathsByAddr == nil {
+		c.scionPathsByAddr = make(map[scionAddrKey]scionPathKey)
+	}
+	c.scionPathsByAddr[scionAddrKey{ia: peerIA, addr: hostAddr}] = k
+}
+
+// updateActiveSCIONPathLocking updates the reverse index, acquiring c.mu.
+func (c *Conn) updateActiveSCIONPathLocking(peerIA addr.IA, hostAddr netip.AddrPort, k scionPathKey) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	c.setActiveSCIONPath(peerIA, hostAddr, k)
+}
+
+// scionPathString returns the human-readable display string for a SCION path
+// key. Returns "scion:<key>" as fallback if the key is not found in the
+// registry. Acquires c.mu.
+func (c *Conn) scionPathString(key scionPathKey) string {
+	if !key.IsSet() {
+		return ""
+	}
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	if pi, ok := c.scionPaths[key]; ok {
+		return pi.String()
+	}
+	return fmt.Sprintf("scion:%d", key)
+}
+
+// receiveSCION is the conn.ReceiveFunc for SCION packets. It reads from the
+// SCION connection and dispatches disco or WireGuard packets.
+//
+// Unlike receiveIP, this function handles read errors internally and never
+// propagates them to WireGuard. This is critical because WireGuard's
+// RoutineReceiveIncoming exits the goroutine permanently after 10 consecutive
+// temporary errors, and we need to survive SCION socket death + reconnection.
+//
+// The read blocks indefinitely (like IPv4/IPv6 sockets). On shutdown,
+// closeSCIONBindLocked sets an immediate deadline to unblock the read.
+// On socket swap (reconnection from the send path), the old socket is
+// closed which unblocks the read with net.ErrClosed; the loop then
+// re-reads c.pconnSCION to pick up the new socket.
+//
+// When the underlay socket is available, packets are read in batches via
+// recvmmsg and parsed with lightweight slayers.SCION decoding. Otherwise,
+// falls back to single-packet snet.Conn.ReadFrom.
+func (c *Conn) receiveSCION(buffs [][]byte, sizes []int, eps []wgconn.Endpoint) (int, error) {
+	sc := c.pconnSCION.Load()
+	if sc == nil {
+		// SCION not connected yet. Wait and retry instead of blocking
+		// forever, so that mid-session SCION connections (e.g. from
+		// ReconfigureSCION on Android) can start receiving.
+		select {
+		case <-c.donec:
+			return 0, net.ErrClosed
+		case <-time.After(5 * time.Second):
+		}
+		sc = c.pconnSCION.Load()
+		if sc == nil {
+			return 0, nil // return zero to let WireGuard call us again
+		}
+	}
+
+	for {
+		// Check for graceful shutdown.
+		select {
+		case <-c.donec:
+			return 0, net.ErrClosed
+		default:
+		}
+
+		// Re-read pconnSCION — it may have been swapped by reconnectSCION.
+		sc = c.pconnSCION.Load()
+		if sc == nil {
+			// Socket was closed and reconnection failed. Retry.
+			select {
+			case <-c.donec:
+				return 0, net.ErrClosed
+			case <-time.After(5 * time.Second):
+			}
+			c.retrySCIONConnect()
+			continue
+		}
+
+		// Fast path: batch read from underlay via recvmmsg.
+		// No read deadline — blocks indefinitely like IPv4/IPv6 sockets.
+		// On shutdown, closeSCIONBindLocked sets an immediate deadline.
+		// On reconnection, the old socket is closed → net.ErrClosed.
+		if sc.underlayXPC != nil {
+			n, err := c.receiveSCIONBatch(sc.underlayXPC, buffs, sizes, eps)
+			if n > 0 {
+				return n, nil
+			}
+			if err != nil {
+				select {
+				case <-c.donec:
+					return 0, net.ErrClosed
+				default:
+				}
+				if errors.Is(err, net.ErrClosed) || isTimeoutError(err) {
+					// Socket closed (reconnection or shutdown) or
+					// deadline set by closeSCIONBindLocked — re-check.
+					continue
+				}
+				c.logf("magicsock: SCION read error: %v", err)
+				continue
+			}
+			// n == 0 and no error means all packets were disco/filtered.
+			continue
+		}
+
+		// Slow path: single-packet snet.Conn.ReadFrom.
+		// No read deadline — blocks indefinitely.
+		n, srcAddr, err := sc.readFrom(buffs[0])
+		if err != nil {
+			select {
+			case <-c.donec:
+				return 0, net.ErrClosed
+			default:
+			}
+			if errors.Is(err, net.ErrClosed) || isTimeoutError(err) {
+				continue
+			}
+			c.logf("magicsock: SCION read error: %v", err)
+			continue
+		}
+		if n == 0 {
+			continue
+		}
+
+		c.lastSCIONRecv.StoreAtomic(mono.Now())
+
+		b := buffs[0][:n]
+		srcHostAddr := srcAddr.Host.AddrPort()
+
+		pt, _ := packetLooksLike(b)
+		if pt == packetLooksLikeDisco {
+			// Slow path disco: snet.Conn.ReadFrom returns a pre-reversed
+			// path suitable for replies, so use srcAddr directly.
+			srcEpAddr := epAddr{ap: srcHostAddr}
+			c.mu.Lock()
+			sk := c.scionPathsByAddr[scionAddrKey{ia: srcAddr.IA, addr: srcHostAddr}]
+			if !sk.IsSet() {
+				pi := &scionPathInfo{
+					peerIA:    srcAddr.IA,
+					hostAddr:  srcHostAddr,
+					replyPath: srcAddr,
+				}
+				pi.buildDisplayStr()
+				sk = c.registerSCIONPath(pi)
+				c.setActiveSCIONPath(srcAddr.IA, srcHostAddr, sk)
+			}
+			c.mu.Unlock()
+			srcEpAddr.scionKey = sk
+			c.handleDiscoMessage(b, srcEpAddr, false, key.NodePublic{}, discoRXPathSCION)
+			continue
+		}
+
+		if !c.havePrivateKey.Load() {
+			continue
+		}
+
+		srcEpAddr := epAddr{ap: srcHostAddr}
+		c.mu.Lock()
+		ep, ok := c.peerMap.endpointForEpAddr(srcEpAddr)
+		c.mu.Unlock()
+		if !ok {
+			sizes[0] = n
+			eps[0] = &lazyEndpoint{c: c, src: srcEpAddr}
+			return 1, nil
+		}
+
+		now := mono.Now()
+		ep.lastRecvUDPAny.StoreAtomic(now)
+		ep.noteRecvActivity(srcEpAddr, now)
+		if c.metrics != nil {
+			c.metrics.inboundPacketsSCIONTotal.Add(1)
+			c.metrics.inboundBytesSCIONTotal.Add(int64(n))
+		}
+		sizes[0] = n
+		eps[0] = ep
+		return 1, nil
+	}
+}
+
+// receiveSCIONShim is the conn.ReceiveFunc for the legacy dispatcher shim
+// socket (port 30041). It reads SCION packets identically to the main socket's
+// batch path, reusing receiveSCIONBatch for all parsing and disco handling.
+//
+// Unlike receiveSCION, this function does not trigger reconnections (that is
+// the main socket's responsibility) and has no slow-path fallback (the shim
+// is always a raw *net.UDPConn).
+func (c *Conn) receiveSCIONShim(buffs [][]byte, sizes []int, eps []wgconn.Endpoint) (int, error) {
+	sc := c.pconnSCION.Load()
+	if sc == nil {
+		// SCION not connected yet. Wait for mid-session connect.
+		select {
+		case <-c.donec:
+			return 0, net.ErrClosed
+		case <-time.After(5 * time.Second):
+		}
+		sc = c.pconnSCION.Load()
+		if sc == nil || sc.shimXPC == nil {
+			return 0, nil
+		}
+	} else if sc.shimXPC == nil {
+		// Connected but no dispatcher shim. shimXPC is immutable per
+		// scionConn, so poll infrequently — only a full reconnect
+		// (new scionConn) could create one.
+		select {
+		case <-c.donec:
+			return 0, net.ErrClosed
+		case <-time.After(30 * time.Second):
+		}
+		sc = c.pconnSCION.Load()
+		if sc == nil || sc.shimXPC == nil {
+			return 0, nil
+		}
+	}
+
+	for {
+		select {
+		case <-c.donec:
+			return 0, net.ErrClosed
+		default:
+		}
+
+		// Re-read pconnSCION — it may have been swapped by reconnectSCION.
+		sc = c.pconnSCION.Load()
+		if sc == nil {
+			// Main socket reconnection in progress. Wait and retry;
+			// the reconnect may or may not rebind port 30041.
+			select {
+			case <-c.donec:
+				return 0, net.ErrClosed
+			case <-time.After(5 * time.Second):
+			}
+			continue
+		}
+		if sc.shimXPC == nil {
+			// Shim was not created for this connection (immutable per scionConn).
+			// Poll infrequently — only a full reconnect could add one.
+			select {
+			case <-c.donec:
+				return 0, net.ErrClosed
+			case <-time.After(30 * time.Second):
+			}
+			continue
+		}
+
+		n, err := c.receiveSCIONBatch(sc.shimXPC, buffs, sizes, eps)
+		if n > 0 {
+			return n, nil
+		}
+		if err != nil {
+			select {
+			case <-c.donec:
+				return 0, net.ErrClosed
+			default:
+			}
+			if errors.Is(err, net.ErrClosed) || isTimeoutError(err) {
+				continue
+			}
+			c.logf("magicsock: SCION shim read error: %v", err)
+			continue
+		}
+		// n == 0 and no error means all packets were disco/filtered.
+		continue
+	}
+}
+
+// receiveSCIONBatch reads a batch of raw SCION packets from the underlay
+// socket via recvmmsg, parses SCION+UDP headers with slayers, and copies
+// payloads into WireGuard's buffs. Disco packets are handled inline and
+// not reported to the caller.
+func (c *Conn) receiveSCIONBatch(xpc scionBatchRW, buffs [][]byte, sizes []int, eps []wgconn.Endpoint) (int, error) {
+	batch := scionRecvBatchPool.Get().(*scionRecvBatch)
+	defer putScionRecvBatch(batch)
+
+	n := len(buffs)
+	if n > scionMaxBatchSize {
+		n = scionMaxBatchSize
+	}
+
+	numMsgs, err := xpc.ReadBatch(batch.msgs[:n], 0)
+	if err != nil {
+		return 0, err
+	}
+
+	reportToCaller := false
+	count := 0
+	for i := 0; i < numMsgs; i++ {
+		msg := &batch.msgs[i]
+		if msg.N == 0 {
+			sizes[count] = 0
+			continue
+		}
+
+		srcIA, srcHostAddr, payload, rawPath, ok := parseSCIONPacket(
+			msg.Buffers[0][:msg.N], &batch.scn)
+		if !ok || len(payload) == 0 {
+			continue
+		}
+
+		// Copy payload into WireGuard's buffer.
+		pn := copy(buffs[count], payload)
+
+		c.lastSCIONRecv.StoreAtomic(mono.Now())
+
+		pt, _ := packetLooksLike(buffs[count][:pn])
+		if pt == packetLooksLikeDisco {
+			// Extract underlay source address (border router) for reply NextHop.
+			var nextHop *net.UDPAddr
+			if ua, ok := msg.Addr.(*net.UDPAddr); ok {
+				nextHop = ua
+			}
+			c.handleSCIONDisco(buffs[count][:pn], srcIA, srcHostAddr, rawPath, nextHop)
+			continue
+		}
+
+		if !c.havePrivateKey.Load() {
+			continue
+		}
+
+		srcEpAddr := epAddr{ap: srcHostAddr}
+		c.mu.Lock()
+		ep, ok := c.peerMap.endpointForEpAddr(srcEpAddr)
+		c.mu.Unlock()
+		if !ok {
+			sizes[count] = pn
+			eps[count] = &lazyEndpoint{c: c, src: srcEpAddr}
+			count++
+			reportToCaller = true
+			continue
+		}
+
+		now := mono.Now()
+		ep.lastRecvUDPAny.StoreAtomic(now)
+		ep.noteRecvActivity(srcEpAddr, now)
+		if c.metrics != nil {
+			c.metrics.inboundPacketsSCIONTotal.Add(1)
+			c.metrics.inboundBytesSCIONTotal.Add(int64(pn))
+		}
+		sizes[count] = pn
+		eps[count] = ep
+		count++
+		reportToCaller = true
+	}
+
+	if reportToCaller {
+		return count, nil
+	}
+	return 0, nil
+}
+
+// handleSCIONDisco handles a disco packet received on the batch path.
+// It looks up or registers a SCION path entry and dispatches to handleDiscoMessage.
+// For first-contact, the raw path bytes are reversed to build a reply path.
+// nextHop is the underlay border router address from the incoming packet.
+func (c *Conn) handleSCIONDisco(b []byte, srcIA addr.IA, srcHostAddr netip.AddrPort, rawPath []byte, nextHop *net.UDPAddr) {
+	srcEpAddr := epAddr{ap: srcHostAddr}
+	c.mu.Lock()
+	sk := c.scionPathsByAddr[scionAddrKey{ia: srcIA, addr: srcHostAddr}]
+	if !sk.IsSet() {
+		// First disco packet from this SCION peer — build a reply path
+		// by reversing the raw SCION path from the incoming packet.
+		replyAddr := buildSCIONReplyAddr(srcIA, srcHostAddr, rawPath, nextHop)
+		pi := &scionPathInfo{
+			peerIA:    srcIA,
+			hostAddr:  srcHostAddr,
+			replyPath: replyAddr,
+		}
+		pi.buildDisplayStr()
+		sk = c.registerSCIONPath(pi)
+		c.setActiveSCIONPath(srcIA, srcHostAddr, sk)
+	}
+	c.mu.Unlock()
+	srcEpAddr.scionKey = sk
+	c.handleDiscoMessage(b, srcEpAddr, false, key.NodePublic{}, discoRXPathSCION)
+}
+
+// isTimeoutError reports whether err is a network timeout (from SetReadDeadline).
+func isTimeoutError(err error) bool {
+	var netErr net.Error
+	return errors.As(err, &netErr) && netErr.Timeout()
+}
+
+// scionDaemonAlive probes the SCION daemon connector to check if it's
+// still responsive. For the embedded connector this is trivial (field read);
+// for external daemons it's a gRPC call confirming the process is alive.
+func (c *Conn) scionDaemonAlive() bool {
+	sc := c.pconnSCION.Load()
+	if sc == nil || sc.daemon == nil {
+		return false
+	}
+	ctx, cancel := context.WithTimeout(c.connCtx, scionDaemonProbeTimeout)
+	defer cancel()
+	_, err := sc.daemon.LocalIA(ctx)
+	return err == nil
+}
+
+// reconnectSCIONSocket attempts a socket-only reconnection: close the
+// socket but keep the daemon connector and topology, then call
+// finishSCIONConnect to create a new socket with the existing connector.
+// Returns true on success.
+func (c *Conn) reconnectSCIONSocket() bool {
+	sc := c.pconnSCION.Load()
+	if sc == nil {
+		return false
+	}
+
+	savedDaemon := sc.daemon
+	savedTopo := sc.topo
+
+	// Close socket, release the port for rebinding.
+	sc.closeSocket()
+	c.pconnSCION.Store(nil)
+
+	newSC, err := finishSCIONConnect(c.connCtx, savedDaemon, savedTopo, c.logf, c.netMon)
+	if err != nil {
+		c.logf("magicsock: SCION socket-only reconnect failed: %v", err)
+		return false
+	}
+
+	c.pconnSCION.Store(newSC)
+	c.logf("magicsock: SCION socket-only reconnect succeeded, local IA: %s", newSC.localIA)
+	return true
+}
+
+// reconnectSCION performs tiered SCION reconnection:
+//   - Tier 1: If the daemon connector is alive, do a socket-only reconnect
+//     (avoids expensive bootstrap: DNS SRV, topology fetch, TRCs, etc.)
+//   - Tier 2: Full bootstrap — close everything, trySCIONConnect from scratch
+//
+// The receiveSCION loop picks up the new socket on the next iteration
+// because the old socket's close unblocks the read with net.ErrClosed.
+func (c *Conn) reconnectSCION() {
+	// Tier 1: socket-only reconnect if daemon is alive.
+	if c.scionDaemonAlive() {
+		c.logf("magicsock: SCION daemon alive, trying socket-only reconnect")
+		if c.reconnectSCIONSocket() {
+			c.rediscoverAllSCIONPaths()
+			return
+		}
+		c.logf("magicsock: SCION socket-only reconnect failed, falling through to full bootstrap")
+	}
+
+	// Tier 2: full bootstrap.
+	c.logf("magicsock: SCION doing full bootstrap reconnect")
+	oldSC := c.pconnSCION.Load()
+
+	// Close old connection first — we must release the port before binding
+	// the new socket. When TS_SCION_PORT is set, both sockets would try
+	// to bind the same port. This means there's a brief window where
+	// pconnSCION is nil and sends will fail, but that's acceptable —
+	// the endpoint was already dead anyway.
+	if oldSC != nil {
+		oldSC.close()
+	}
+	c.pconnSCION.Store(nil)
+
+	newSC, err := trySCIONConnect(c.connCtx, c.logf, c.netMon)
+	if err != nil {
+		c.logf("magicsock: SCION reconnect failed: %v", err)
+		return
+	}
+
+	c.pconnSCION.Store(newSC)
+	c.logf("magicsock: SCION reconnected successfully, local IA: %s", newSC.localIA)
+	c.rediscoverAllSCIONPaths()
+}
+
+// retrySCIONConnect attempts to re-establish a SCION connection when
+// pconnSCION is nil (previous reconnect attempt failed).
+func (c *Conn) retrySCIONConnect() {
+	if c.pconnSCION.Load() != nil {
+		return // another goroutine beat us to it
+	}
+	newSC, err := trySCIONConnect(c.connCtx, c.logf, c.netMon)
+	if err != nil {
+		c.logf("magicsock: SCION reconnect retry failed: %v", err)
+		return
+	}
+	c.pconnSCION.Store(newSC)
+	c.lastSCIONRecv.StoreAtomic(mono.Now())
+	c.logf("magicsock: SCION reconnect retry succeeded, local IA: %s", newSC.localIA)
+	c.rediscoverAllSCIONPaths()
+	c.discoverNewSCIONPeers()
+	c.ReSTUN("scion-connected")
+}
+
+// rediscoverAllSCIONPaths triggers path re-discovery for all endpoints that
+// have SCION state. This is called after reconnecting the SCION socket to
+// ensure paths reference the new connection.
+func (c *Conn) rediscoverAllSCIONPaths() {
+	c.mu.Lock()
+	var peers []struct {
+		ep       *endpoint
+		peerIA   addr.IA
+		hostAddr netip.AddrPort
+	}
+	c.peerMap.forEachEndpoint(func(ep *endpoint) {
+		ep.mu.Lock()
+		if ep.scionState != nil {
+			peers = append(peers, struct {
+				ep       *endpoint
+				peerIA   addr.IA
+				hostAddr netip.AddrPort
+			}{ep, ep.scionState.peerIA, ep.scionState.hostAddr})
+		}
+		ep.mu.Unlock()
+	})
+	c.mu.Unlock()
+
+	for _, p := range peers {
+		go p.ep.discoverSCIONPathAsync(p.peerIA, p.hostAddr)
+	}
+}
+
+// discoverNewSCIONPeers scans all known peers for SCION service advertisements
+// and triggers path discovery for any peers that don't yet have scionState.
+// Called after a successful SCION connect to handle the case where the netmap
+// was processed before SCION was available.
+func (c *Conn) discoverNewSCIONPeers() {
+	c.mu.Lock()
+	peers := c.peers
+	c.mu.Unlock()
+
+	for i := range peers.Len() {
+		peer := peers.At(i)
+		peerIA, hostAddr, ok := scionServiceFromPeer(peer)
+		if !ok {
+			continue
+		}
+		c.mu.Lock()
+		ep, ok := c.peerMap.endpointForNodeID(peer.ID())
+		c.mu.Unlock()
+		if !ok || ep == nil {
+			continue
+		}
+		ep.mu.Lock()
+		hasScionState := ep.scionState != nil
+		ep.mu.Unlock()
+		if hasScionState {
+			continue // already tracked by rediscoverAllSCIONPaths
+		}
+		c.logf("magicsock: SCION peer %s at %s, discovering paths (post-connect)...", peerIA, hostAddr)
+		go ep.discoverSCIONPathAsync(peerIA, hostAddr)
+	}
+}
+
+// discoverSCIONPaths queries the SCION daemon for paths to the given peer IA,
+// deduplicates by fingerprint, selects the top N by latency, and stores them
+// in the path registry. Returns the scionPathKeys for the registered paths
+// (first element is the lowest-latency path).
+func (c *Conn) discoverSCIONPaths(ctx context.Context, peerIA addr.IA, hostAddr netip.AddrPort) ([]scionPathKey, error) {
+	sc := c.pconnSCION.Load()
+	if sc == nil {
+		return nil, errNoSCION
+	}
+
+	paths, err := sc.daemon.Paths(ctx, peerIA, sc.localIA, daemon.PathReqFlags{Refresh: false})
+	if err != nil {
+		return nil, fmt.Errorf("querying SCION paths to %s: %w", peerIA, err)
+	}
+	if len(paths) == 0 {
+		return nil, fmt.Errorf("no SCION paths to %s", peerIA)
+	}
+
+	// Deduplicate by fingerprint (topologically identical paths).
+	seen := make(map[snet.PathFingerprint]bool)
+	var unique []pathWithMeta
+	for _, p := range paths {
+		var fp snet.PathFingerprint
+		if md := p.Metadata(); md != nil {
+			fp = md.Fingerprint()
+		}
+		if fp != "" && seen[fp] {
+			continue
+		}
+		if fp != "" {
+			seen[fp] = true
+		}
+		unique = append(unique, pathWithMeta{
+			path:        p,
+			fingerprint: fp,
+			latency:     totalPathLatency(p),
+		})
+	}
+
+	// Select paths balancing latency and topological diversity.
+	maxPaths := scionMaxProbePaths()
+	unique = selectDiversePaths(unique, maxPaths)
+
+	// Register each path.
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	keys := make([]scionPathKey, 0, len(unique))
+	for _, u := range unique {
+		var expiry time.Time
+		var mtu uint16
+		if md := u.path.Metadata(); md != nil {
+			expiry = md.Expiry
+			mtu = md.MTU
+		}
+		pi := &scionPathInfo{
+			peerIA:      peerIA,
+			hostAddr:    hostAddr,
+			fingerprint: u.fingerprint,
+			path:        u.path,
+			expiry:      expiry,
+			mtu:         mtu,
+		}
+		pi.buildCachedDst()
+		pi.buildDisplayStr()
+		if sc := c.pconnSCION.Load(); sc != nil {
+			pi.fastPath = buildSCIONFastPath(sc, pi)
+		}
+		keys = append(keys, c.registerSCIONPath(pi))
+	}
+	// Set the first (lowest-latency) path as active for the reverse index.
+	if len(keys) > 0 {
+		c.setActiveSCIONPath(peerIA, hostAddr, keys[0])
+	}
+	return keys, nil
+}
+
+// totalPathLatency returns the sum of all hop latencies for a SCION path.
+// Returns a large value if latency information is unavailable.
+func totalPathLatency(p snet.Path) time.Duration {
+	md := p.Metadata()
+	if md == nil || len(md.Latency) == 0 {
+		return time.Hour // large sentinel for unknown latency
+	}
+	var total time.Duration
+	for _, l := range md.Latency {
+		if l < 0 {
+			// LatencyUnset — treat as unknown
+			total += scionUnsetHopLatency
+		} else {
+			total += l
+		}
+	}
+	return total
+}
+
+// pathWithMeta pairs a SCION path with its fingerprint and estimated latency
+// for use in path selection and diversity algorithms.
+type pathWithMeta struct {
+	path        snet.Path
+	fingerprint snet.PathFingerprint
+	latency     time.Duration
+}
+
+// debugSCIONDiversityThreshold is the TS_SCION_DIVERSITY_THRESHOLD envknob
+// controlling the latency penalty threshold (in ms) for diversity selection.
+// Default 50ms.
+var debugSCIONDiversityThreshold = envknob.RegisterInt("TS_SCION_DIVERSITY_THRESHOLD")
+
+// scionDiversityThreshold returns the latency threshold for diversity scoring.
+func scionDiversityThreshold() time.Duration {
+	if v := debugSCIONDiversityThreshold(); v > 0 {
+		return time.Duration(v) * time.Millisecond
+	}
+	return 50 * time.Millisecond
+}
+
+// interfaceOverlap computes the fraction of interfaces in path a that also
+// appear in path b: |a ∩ b| / |a|. Returns 0.0 if either path has no
+// interface metadata (unknown paths are assumed diverse).
+func interfaceOverlap(a, b snet.Path) float64 {
+	mdA := a.Metadata()
+	mdB := b.Metadata()
+	if mdA == nil || mdB == nil || len(mdA.Interfaces) == 0 || len(mdB.Interfaces) == 0 {
+		return 0.0
+	}
+
+	bSet := make(map[snet.PathInterface]bool, len(mdB.Interfaces))
+	for _, iface := range mdB.Interfaces {
+		bSet[iface] = true
+	}
+
+	var overlap int
+	for _, iface := range mdA.Interfaces {
+		if bSet[iface] {
+			overlap++
+		}
+	}
+	return float64(overlap) / float64(len(mdA.Interfaces))
+}
+
+// selectDiversePaths selects up to maxPaths from candidates, balancing low
+// latency with topological diversity. It uses a greedy algorithm:
+//  1. Sort candidates by latency ascending, pick the best.
+//  2. For each subsequent slot, score remaining candidates by diversity
+//     (1 − max overlap with selected) minus latency penalty.
+//  3. Fill remaining slots by pure latency if no diversity benefit.
+func selectDiversePaths(candidates []pathWithMeta, maxPaths int) []pathWithMeta {
+	if len(candidates) <= maxPaths {
+		sort.Slice(candidates, func(i, j int) bool {
+			return candidates[i].latency < candidates[j].latency
+		})
+		return candidates
+	}
+
+	// Sort by latency ascending.
+	sort.Slice(candidates, func(i, j int) bool {
+		return candidates[i].latency < candidates[j].latency
+	})
+
+	threshold := scionDiversityThreshold()
+	selected := make([]pathWithMeta, 0, maxPaths)
+	used := make([]bool, len(candidates))
+
+	// Always pick the lowest-latency path first.
+	selected = append(selected, candidates[0])
+	used[0] = true
+	bestLatency := candidates[0].latency
+
+	for len(selected) < maxPaths {
+		bestScore := -1.0
+		bestIdx := -1
+
+		for i, c := range candidates {
+			if used[i] {
+				continue
+			}
+
+			// Compute diversity score: 1 − max overlap with any selected path.
+			var maxOverlap float64
+			for _, s := range selected {
+				if ov := interfaceOverlap(c.path, s.path); ov > maxOverlap {
+					maxOverlap = ov
+				}
+			}
+			diversityScore := 1.0 - maxOverlap
+
+			// Latency penalty: how much slower than the best path, normalized.
+			var latencyPenalty float64
+			if threshold > 0 {
+				latencyPenalty = float64(c.latency-bestLatency) / float64(threshold)
+			}
+
+			score := diversityScore - latencyPenalty
+			if score > bestScore {
+				bestScore = score
+				bestIdx = i
+			}
+		}
+
+		if bestIdx < 0 || bestScore <= 0 {
+			// No diversity benefit; fill remaining by pure latency.
+			for i, c := range candidates {
+				if used[i] {
+					continue
+				}
+				selected = append(selected, c)
+				if len(selected) >= maxPaths {
+					break
+				}
+			}
+			break
+		}
+
+		selected = append(selected, candidates[bestIdx])
+		used[bestIdx] = true
+	}
+
+	return selected
+}
+
+// refreshSCIONPaths runs in a background goroutine, periodically refreshing
+// SCION paths before they expire. It uses exponential backoff when the SCION
+// daemon is unreachable.
+func (c *Conn) refreshSCIONPaths() {
+	const (
+		baseInterval = 30 * time.Second
+		maxBackoff   = 10 * time.Minute
+	)
+	ticker := time.NewTicker(baseInterval)
+	defer ticker.Stop()
+
+	var consecutiveFailures int
+	for {
+		select {
+		case <-c.donec:
+			return
+		case <-ticker.C:
+			if consecutiveFailures > 0 {
+				backoff := baseInterval * time.Duration(1<<min(consecutiveFailures, 5))
+				if backoff > maxBackoff {
+					backoff = maxBackoff
+				}
+				ticker.Reset(backoff)
+			}
+			if err := c.refreshSCIONPathsOnce(); err != nil {
+				consecutiveFailures++
+				if consecutiveFailures == 1 || consecutiveFailures&(consecutiveFailures-1) == 0 {
+					c.logf("magicsock: SCION path refresh failed (%d consecutive): %v",
+						consecutiveFailures, err)
+				}
+			} else {
+				if consecutiveFailures > 0 {
+					ticker.Reset(baseInterval)
+				}
+				consecutiveFailures = 0
+			}
+		}
+	}
+}
+
+func (c *Conn) refreshSCIONPathsOnce() error {
+	sc := c.pconnSCION.Load()
+	if sc == nil {
+		return nil
+	}
+
+	c.mu.Lock()
+	// Snapshot the current paths under lock.
+	pathsCopy := make(map[scionPathKey]*scionPathInfo, len(c.scionPaths))
+	for k, v := range c.scionPaths {
+		pathsCopy[k] = v
+	}
+	c.mu.Unlock()
+
+	// Group paths by peerIA so we query the daemon once per peer.
+	type peerGroup struct {
+		peerIA      addr.IA
+		hostAddr    netip.AddrPort
+		needRefresh bool
+		keys        []scionPathKey
+		infos       []*scionPathInfo
+	}
+	groups := make(map[addr.IA]*peerGroup)
+	now := time.Now()
+	for k, pi := range pathsCopy {
+		pi.mu.Lock()
+		peerIA := pi.peerIA
+		hostAddr := pi.hostAddr
+		needsRefresh := !pi.expiry.IsZero() && now.After(pi.expiry.Add(-1*time.Minute))
+		pi.mu.Unlock()
+
+		g := groups[peerIA]
+		if g == nil {
+			g = &peerGroup{peerIA: peerIA, hostAddr: hostAddr}
+			groups[peerIA] = g
+		}
+		g.keys = append(g.keys, k)
+		g.infos = append(g.infos, pi)
+		if needsRefresh {
+			g.needRefresh = true
+		}
+	}
+
+	ctx, cancel := context.WithTimeout(c.connCtx, 10*time.Second)
+	defer cancel()
+
+	var lastErr error
+	for _, g := range groups {
+		if !g.needRefresh {
+			continue
+		}
+
+		daemonPaths, err := sc.daemon.Paths(ctx, g.peerIA, sc.localIA, daemon.PathReqFlags{Refresh: true})
+		if err != nil || len(daemonPaths) == 0 {
+			c.logf("magicsock: SCION path refresh for %s failed: %v", g.peerIA, err)
+			if err != nil {
+				lastErr = err
+			} else {
+				lastErr = fmt.Errorf("no paths to %s", g.peerIA)
+			}
+			continue
+		}
+
+		// Index daemon paths by fingerprint for matching.
+		type daemonPathEntry struct {
+			path snet.Path
+			fp   snet.PathFingerprint
+		}
+		var daemonByFP []daemonPathEntry
+		for _, dp := range daemonPaths {
+			var fp snet.PathFingerprint
+			if md := dp.Metadata(); md != nil {
+				fp = md.Fingerprint()
+			}
+			daemonByFP = append(daemonByFP, daemonPathEntry{
+				path: dp,
+				fp:   fp,
+			})
+		}
+
+		// Find the best daemon path for fallback use.
+		bestDaemon := daemonPaths[0]
+		bestDaemonLat := totalPathLatency(bestDaemon)
+		for _, p := range daemonPaths[1:] {
+			lat := totalPathLatency(p)
+			if lat < bestDaemonLat {
+				bestDaemon = p
+				bestDaemonLat = lat
+			}
+		}
+
+		// Match existing registered paths to daemon paths by fingerprint.
+		// Unmatched paths with known fingerprints (disappeared from daemon)
+		// have their refreshMissCount incremented. When the count exceeds
+		// scionStalePathThreshold, the path is removed. Paths with empty
+		// fingerprints (no metadata) get the best daemon path as fallback.
+		var stalePaths []scionPathKey
+		for i, pi := range g.infos {
+			pi.mu.Lock()
+			fp := pi.fingerprint
+			pi.mu.Unlock()
+
+			var matched snet.Path
+			if fp != "" {
+				for _, d := range daemonByFP {
+					if d.fp == fp {
+						matched = d.path
+						break
+					}
+				}
+				if matched == nil {
+					// Known fingerprint disappeared from daemon results.
+					pi.mu.Lock()
+					pi.refreshMissCount++
+					if pi.refreshMissCount >= scionStalePathThreshold {
+						stalePaths = append(stalePaths, g.keys[i])
+					}
+					pi.mu.Unlock()
+					continue
+				}
+			} else {
+				// No fingerprint (missing metadata). Use best daemon path.
+				matched = bestDaemon
+			}
+
+			pi.mu.Lock()
+			pi.refreshMissCount = 0
+			pi.path = matched
+			if md := matched.Metadata(); md != nil {
+				pi.fingerprint = md.Fingerprint()
+				pi.expiry = md.Expiry
+				pi.mtu = md.MTU
+			}
+			pi.buildCachedDst()
+			pi.buildDisplayStr()
+			pi.fastPath = buildSCIONFastPath(sc, pi)
+			pi.mu.Unlock()
+		}
+
+		// Remove stale paths that have been absent for too many refresh cycles.
+		if len(stalePaths) > 0 {
+			c.mu.Lock()
+			for _, k := range stalePaths {
+				pathStr := fmt.Sprintf("scion:%d", k)
+				if pi, ok := c.scionPaths[k]; ok {
+					pathStr = pi.String()
+				}
+				c.logf("magicsock: SCION path stale for %s, removing %s", g.peerIA, pathStr)
+				c.unregisterSCIONPath(k)
+			}
+			c.mu.Unlock()
+			c.cleanStaleSCIONPathFromEndpoints(stalePaths, g.peerIA)
+		}
+	}
+
+	// Soft refresh pass: for groups that did NOT need hard refresh, check
+	// if new paths have appeared in the daemon's cache. This discovers new
+	// better paths that become available mid-session without waiting for
+	// expiry-driven hard refresh.
+	const softRefreshInterval = 5 * time.Minute
+	for _, g := range groups {
+		if g.needRefresh {
+			continue // already refreshed above
+		}
+		c.mu.Lock()
+		lastSoft := c.scionSoftRefreshAt[g.peerIA]
+		c.mu.Unlock()
+		if !lastSoft.IsZero() && now.Sub(lastSoft) < softRefreshInterval {
+			continue
+		}
+
+		daemonPaths, err := sc.daemon.Paths(ctx, g.peerIA, sc.localIA, daemon.PathReqFlags{Refresh: false})
+		if err != nil || len(daemonPaths) == 0 {
+			continue
+		}
+
+		// Collect existing fingerprints for this group.
+		knownFPs := make(map[snet.PathFingerprint]bool, len(g.infos))
+		for _, pi := range g.infos {
+			pi.mu.Lock()
+			if pi.fingerprint != "" {
+				knownFPs[pi.fingerprint] = true
+			}
+			pi.mu.Unlock()
+		}
+
+		// Filter to paths with new fingerprints.
+		maxSlots := scionMaxProbePaths()
+		available := maxSlots - len(g.keys)
+		if available <= 0 {
+			c.mu.Lock()
+			mak.Set(&c.scionSoftRefreshAt, g.peerIA, now)
+			c.mu.Unlock()
+			continue
+		}
+
+		var newPaths []snet.Path
+		for _, dp := range daemonPaths {
+			var fp snet.PathFingerprint
+			if md := dp.Metadata(); md != nil {
+				fp = md.Fingerprint()
+			}
+			if fp == "" || knownFPs[fp] {
+				continue
+			}
+			newPaths = append(newPaths, dp)
+			if len(newPaths) >= available {
+				break
+			}
+		}
+
+		if len(newPaths) > 0 {
+			newKeys := c.addNewSCIONPathsForPeer(g.peerIA, g.hostAddr, newPaths)
+			for i, k := range newKeys {
+				c.logf("magicsock: SCION soft refresh for %s: [%d] %s", g.peerIA, i, c.scionPathString(k))
+			}
+		}
+
+		c.mu.Lock()
+		mak.Set(&c.scionSoftRefreshAt, g.peerIA, now)
+		c.mu.Unlock()
+	}
+
+	return lastErr
+}
+
+// addNewSCIONPathsForPeer registers new SCION paths and adds probe states
+// to the corresponding endpoint. Called during soft refresh when new paths
+// appear in the daemon's cache. Returns the registered path keys.
+func (c *Conn) addNewSCIONPathsForPeer(peerIA addr.IA, hostAddr netip.AddrPort, paths []snet.Path) []scionPathKey {
+	sc := c.pconnSCION.Load()
+	if sc == nil {
+		return nil
+	}
+
+	c.mu.Lock()
+	var newKeys []scionPathKey
+	for _, p := range paths {
+		md := p.Metadata()
+		var expiry time.Time
+		var mtu uint16
+		if md != nil {
+			expiry = md.Expiry
+			mtu = md.MTU
+		}
+		var fp snet.PathFingerprint
+		if md != nil {
+			fp = md.Fingerprint()
+		}
+		pi := &scionPathInfo{
+			peerIA:      peerIA,
+			hostAddr:    hostAddr,
+			fingerprint: fp,
+			path:        p,
+			expiry:      expiry,
+			mtu:         mtu,
+		}
+		pi.buildCachedDst()
+		pi.buildDisplayStr()
+		pi.fastPath = buildSCIONFastPath(sc, pi)
+		k := c.registerSCIONPath(pi)
+		newKeys = append(newKeys, k)
+	}
+
+	// Find the endpoint for this peerIA and add probe states.
+	for _, peerInf := range c.peerMap.byNodeKey {
+		ep := peerInf.ep
+		ep.mu.Lock()
+		if ep.scionState != nil && ep.scionState.peerIA == peerIA {
+			for _, k := range newKeys {
+				if _, exists := ep.scionState.paths[k]; !exists {
+					pi := c.scionPaths[k]
+					ep.scionState.paths[k] = &scionPathProbeState{
+						fingerprint: pi.fingerprint,
+						displayStr:  pi.displayStr,
+						healthy:     true,
+					}
+				}
+			}
+		}
+		ep.mu.Unlock()
+	}
+
+	// Recovery: if no endpoint had scionState for this peerIA, the initial
+	// discoverSCIONPathAsync may have failed. Find the endpoint via peerMap
+	// (the plain hostAddr was registered by handlePingLocked from incoming
+	// SCION disco) and initialize scionState so disco probing can begin.
+	if len(newKeys) > 0 {
+		if ep, ok := c.peerMap.endpointForEpAddr(epAddr{ap: hostAddr}); ok {
+			ep.mu.Lock()
+			if ep.scionState == nil {
+				paths := make(map[scionPathKey]*scionPathProbeState, len(newKeys))
+				var activePath scionPathKey
+				for i, k := range newKeys {
+					pi := c.scionPaths[k]
+					paths[k] = &scionPathProbeState{
+						fingerprint: pi.fingerprint,
+						displayStr:  pi.displayStr,
+						healthy:     true,
+					}
+					if i == 0 {
+						activePath = k
+					}
+				}
+				ep.scionState = &scionEndpointState{
+					peerIA:          peerIA,
+					hostAddr:        hostAddr,
+					paths:           paths,
+					activePath:      activePath,
+					lastDiscoveryAt: time.Now(),
+				}
+				c.setActiveSCIONPath(peerIA, hostAddr, activePath)
+				c.logf("magicsock: SCION recovery: initialized scionState for %s with %d paths", peerIA, len(newKeys))
+			}
+			ep.mu.Unlock()
+		}
+	}
+
+	c.mu.Unlock()
+	return newKeys
+}
+
+// cleanStaleSCIONPathFromEndpoints removes stale SCION path keys from all
+// endpoints that reference the given peerIA. If the removed key was the
+// activePath, reassigns to the first remaining path.
+func (c *Conn) cleanStaleSCIONPathFromEndpoints(staleKeys []scionPathKey, peerIA addr.IA) {
+	staleSet := make(map[scionPathKey]bool, len(staleKeys))
+	for _, k := range staleKeys {
+		staleSet[k] = true
+	}
+
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	for _, pi := range c.peerMap.byNodeKey {
+		ep := pi.ep
+		ep.mu.Lock()
+		if ep.scionState == nil || ep.scionState.peerIA != peerIA {
+			ep.mu.Unlock()
+			continue
+		}
+		for k := range ep.scionState.paths {
+			if staleSet[k] {
+				delete(ep.scionState.paths, k)
+			}
+		}
+		if staleSet[ep.scionState.activePath] {
+			ep.scionState.activePath = 0
+			for k := range ep.scionState.paths {
+				ep.scionState.activePath = k
+				break
+			}
+		}
+		ep.mu.Unlock()
+	}
+}
+
+// scionServiceFromPeer extracts SCION service info from a peer node's Services.
+// It checks for a dedicated SCION service entry first, then falls back to
+// checking the peerapi4 Description field (which is used to piggyback SCION
+// info through coord servers that only relay peerapi services).
+func scionServiceFromPeer(n tailcfg.NodeView) (ia addr.IA, hostAddr netip.AddrPort, ok bool) {
+	hi := n.Hostinfo()
+	if !hi.Valid() {
+		return 0, netip.AddrPort{}, false
+	}
+	services := hi.Services()
+	for i := range services.Len() {
+		svc := services.At(i)
+		// Direct SCION service entry.
+		if svc.Proto == tailcfg.SCION {
+			parsedIA, parsedAddr, err := parseSCIONServiceAddr(svc.Description, svc.Port)
+			if err != nil {
+				continue
+			}
+			return parsedIA, parsedAddr, true
+		}
+		// Piggyback: SCION info in peerapi4's Description field.
+		// Format: "scion=ISD-AS,[host-IP]:port"
+		if svc.Proto == tailcfg.PeerAPI4 && strings.HasPrefix(svc.Description, "scion=") {
+			scionDesc := svc.Description[len("scion="):]
+			var addrPart, portStr string
+			// Try bracket notation first: "ISD-AS,[hostIP]:port"
+			if portSep := strings.LastIndex(scionDesc, "]:"); portSep >= 0 {
+				addrPart = scionDesc[:portSep+1]
+				portStr = scionDesc[portSep+2:]
+			} else {
+				// Backward compat: unbracketed "ISD-AS,hostIP:port"
+				lastColon := strings.LastIndex(scionDesc, ":")
+				if lastColon < 0 {
+					continue
+				}
+				addrPart = scionDesc[:lastColon]
+				portStr = scionDesc[lastColon+1:]
+			}
+			var port uint16
+			if _, err := fmt.Sscanf(portStr, "%d", &port); err != nil {
+				continue
+			}
+			parsedIA, parsedAddr, err := parseSCIONServiceAddr(addrPart, port)
+			if err != nil {
+				continue
+			}
+			return parsedIA, parsedAddr, true
+		}
+	}
+	return 0, netip.AddrPort{}, false
+}
+
+// SCIONService returns the SCION service entry to advertise in Hostinfo,
+// or ok=false if SCION is not available.
+func (c *Conn) SCIONService() (svc tailcfg.Service, ok bool) {
+	sc := c.pconnSCION.Load()
+	if sc == nil {
+		return tailcfg.Service{}, false
+	}
+	// snet.Conn.LocalAddr() returns an *snet.UDPAddr; extract host IP and port.
+	localAddr := sc.conn.LocalAddr()
+	hostIP := "127.0.0.1"
+	var scionPort uint16
+	if sa, saOk := localAddr.(*snet.UDPAddr); saOk && sa.Host != nil {
+		if sa.Host.IP != nil {
+			hostIP = sa.Host.IP.String()
+		}
+		scionPort = uint16(sa.Host.Port)
+	}
+	return tailcfg.Service{
+		Proto:       tailcfg.SCION,
+		Port:        scionPort,
+		Description: fmt.Sprintf("%s,[%s]", sc.localIA, hostIP),
+	}, true
+}
+
+// discoverSCIONPathAsync runs SCION path discovery in a goroutine,
+// avoiding blocking updateFromNode which holds the endpoint lock.
+// It self-throttles to at most once every 5 seconds to prevent concurrent
+// launches (from updateFromNode and send error paths) from creating
+// orphaned path entries.
+func (de *endpoint) discoverSCIONPathAsync(peerIA addr.IA, hostAddr netip.AddrPort) {
+	// Throttle: skip if discovery ran recently. This prevents concurrent
+	// launches from orphaning path entries in the registry.
+	de.mu.Lock()
+	if de.scionState != nil && time.Since(de.scionState.lastDiscoveryAt) < 5*time.Second {
+		de.mu.Unlock()
+		return
+	}
+	if de.scionState != nil {
+		de.scionState.lastDiscoveryAt = time.Now()
+	}
+	de.mu.Unlock()
+
+	ctx, cancel := context.WithTimeout(de.c.connCtx, 10*time.Second)
+	defer cancel()
+
+	// Capture old keys before discovering new paths.
+	de.mu.Lock()
+	var oldKeys []scionPathKey
+	if de.scionState != nil {
+		for k := range de.scionState.paths {
+			oldKeys = append(oldKeys, k)
+		}
+	}
+	de.mu.Unlock()
+
+	newKeys, err := de.c.discoverSCIONPaths(ctx, peerIA, hostAddr)
+	if err != nil {
+		de.c.logf("magicsock: SCION path discovery for %s failed: %v", peerIA, err)
+		return
+	}
+
+	// Build set of new keys for fast lookup.
+	newKeySet := make(map[scionPathKey]bool, len(newKeys))
+	for _, k := range newKeys {
+		newKeySet[k] = true
+	}
+
+	// Extract fingerprints and display strings under c.mu (must be acquired before de.mu per lock ordering).
+	type pathSnapshot struct {
+		fingerprint snet.PathFingerprint
+		displayStr  string
+	}
+	de.c.mu.Lock()
+	snapByKey := make(map[scionPathKey]pathSnapshot, len(newKeys))
+	for _, k := range newKeys {
+		if pi := de.c.lookupSCIONPath(k); pi != nil {
+			snapByKey[k] = pathSnapshot{fingerprint: pi.fingerprint, displayStr: pi.displayStr}
+		}
+	}
+	// Clean up old keys that aren't in the new set.
+	for _, k := range oldKeys {
+		if !newKeySet[k] {
+			de.c.unregisterSCIONPath(k)
+		}
+	}
+	de.c.mu.Unlock()
+
+	// Build probe state map, preserving history for surviving paths by fingerprint.
+	de.mu.Lock()
+	var oldProbeByFP map[snet.PathFingerprint]*scionPathProbeState
+	if de.scionState != nil {
+		oldProbeByFP = make(map[snet.PathFingerprint]*scionPathProbeState, len(de.scionState.paths))
+		for _, ps := range de.scionState.paths {
+			if ps.fingerprint != "" {
+				oldProbeByFP[ps.fingerprint] = ps
+			}
+		}
+	}
+
+	newPaths := make(map[scionPathKey]*scionPathProbeState, len(newKeys))
+	for _, k := range newKeys {
+		snap := snapByKey[k]
+		// Preserve existing probe history if the fingerprint matches.
+		if snap.fingerprint != "" && oldProbeByFP != nil {
+			if old, ok := oldProbeByFP[snap.fingerprint]; ok {
+				old.fingerprint = snap.fingerprint // ensure set
+				old.displayStr = snap.displayStr
+				newPaths[k] = old
+				continue
+			}
+		}
+		newPaths[k] = &scionPathProbeState{fingerprint: snap.fingerprint, displayStr: snap.displayStr, healthy: true}
+	}
+
+	activePath := scionPathKey(0)
+	if len(newKeys) > 0 {
+		activePath = newKeys[0]
+	}
+
+	de.scionState = &scionEndpointState{
+		peerIA:          peerIA,
+		hostAddr:        hostAddr,
+		paths:           newPaths,
+		activePath:      activePath,
+		lastDiscoveryAt: time.Now(),
+	}
+	de.mu.Unlock()
+
+	for i, k := range newKeys {
+		active := ""
+		if k == activePath {
+			active = " (active)"
+		}
+		var mtuInfo string
+		de.c.mu.Lock()
+		if pi, ok := de.c.scionPaths[k]; ok {
+			hdrLen := 0
+			if pi.fastPath != nil {
+				hdrLen = len(pi.fastPath.hdr)
+			}
+			maxWG := int(pi.mtu) - hdrLen
+			mtuInfo = fmt.Sprintf(" pathMTU=%d hdr=%d maxWG=%d", pi.mtu, hdrLen, maxWG)
+			// WG overhead: 4 type + 4 receiver + 8 counter + 16 tag = 32 bytes.
+			// Max TUN packet that fits: maxWG - 32.
+			const wgOverhead = 32
+			if pi.mtu > 0 && hdrLen > 0 && maxWG < 1280+wgOverhead {
+				de.c.logf("magicsock: WARNING: SCION path MTU %d too small for TUN 1280 (need %d, have %d for WG payload)",
+					pi.mtu, 1280+wgOverhead+hdrLen, maxWG)
+			}
+		}
+		de.c.mu.Unlock()
+		de.c.logf("magicsock: SCION path to %s: [%d] %s%s%s", peerIA, i, de.c.scionPathString(k), mtuInfo, active)
+	}
+}
+
+// scionKeyForAddr returns the scionPathKey for the given peer IA and host
+// address, or a zero key if not found. O(1) via reverse index.
+func (c *Conn) scionKeyForAddr(peerIA addr.IA, hostAddr netip.AddrPort) scionPathKey {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	return c.scionPathsByAddr[scionAddrKey{ia: peerIA, addr: hostAddr}]
+}
+
+var errNoSCION = fmt.Errorf("SCION not available")
+
+const discoRXPathSCION discoRXPath = "SCION"
+
+// ReconfigureSCION updates SCION configuration at runtime.
+// If disabled, closes the current SCION connection.
+// If enabled, updates envknobs, closes any existing connection, and
+// triggers a fresh reconnection attempt.
+func (c *Conn) ReconfigureSCION(cfg SCIONConfig) {
+	if !cfg.Enabled {
+		c.mu.Lock()
+		c.closeSCIONLocked()
+		c.mu.Unlock()
+		return
+	}
+	if cfg.BootstrapURL != "" {
+		envknob.Setenv("TS_SCION_BOOTSTRAP_URL", cfg.BootstrapURL)
+	}
+	if cfg.Prefer {
+		envknob.Setenv("TS_PREFER_SCION", "true")
+	} else {
+		envknob.Setenv("TS_PREFER_SCION", "")
+	}
+	// Force embedded mode and fresh bootstrap on Android.
+	envknob.Setenv("TS_SCION_EMBEDDED", "1")
+	envknob.Setenv("TS_SCION_FORCE_BOOTSTRAP", "1")
+
+	// Close existing connection (if any) so retrySCIONConnect starts fresh.
+	c.mu.Lock()
+	c.closeSCIONLocked()
+	c.mu.Unlock()
+
+	go c.retrySCIONConnect()
+}
+
+// SCIONStatus returns whether SCION is currently connected and the local IA.
+func (c *Conn) SCIONStatus() (connected bool, localIA string) {
+	sc := c.pconnSCION.Load()
+	if sc == nil {
+		return false, ""
+	}
+	return true, sc.localIA.String()
+}
+
+// populateSCIONPathsLocked fills ps.SCIONPaths from de.scionState.
+// de.mu must be held. c.mu must be held (caller is Conn.UpdateStatus).
+func (de *endpoint) populateSCIONPathsLocked(ps *ipnstate.PeerStatus) {
+	// Don't report paths if SCION is disconnected - they're stale.
+	if de.c.pconnSCION.Load() == nil {
+		return
+	}
+	ss := de.scionState
+	if ss == nil || len(ss.paths) == 0 {
+		return
+	}
+	ps.SCIONPaths = make([]ipnstate.SCIONPathInfo, 0, len(ss.paths))
+	for pk, probe := range ss.paths {
+		info := ipnstate.SCIONPathInfo{
+			Path:    probe.displayStr,
+			Active:  pk == ss.activePath,
+			Healthy: probe.healthy,
+		}
+		lat := probe.latency()
+		if lat < time.Hour {
+			info.LatencyMs = float64(lat.Microseconds()) / 1000.0
+		}
+		// Look up full path info from Conn-level registry for expiry/MTU.
+		if pi, ok := de.c.scionPaths[pk]; ok {
+			if !pi.expiry.IsZero() {
+				info.ExpiresAt = pi.expiry.UTC().Format(time.RFC3339)
+			}
+			if pi.mtu > 0 {
+				info.MTU = int(pi.mtu)
+			}
+		}
+		ps.SCIONPaths = append(ps.SCIONPaths, info)
+	}
+}
diff --git a/wgengine/magicsock/magicsock_scion_conn.go b/wgengine/magicsock/magicsock_scion_conn.go
new file mode 100644
index 0000000000000..af1f0efe5a85b
--- /dev/null
+++ b/wgengine/magicsock/magicsock_scion_conn.go
@@ -0,0 +1,53 @@
+// Copyright (c) Tailscale Inc & contributors
+// SPDX-License-Identifier: BSD-3-Clause
+
+//go:build !ts_omit_scion
+
+package magicsock
+
+import (
+	"context"
+	"time"
+)
+
+// initSCIONLocked tries to set up a SCION connection if not already connected.
+// On success, stores the scionConn and starts the background path refresher.
+// c.mu must be held.
+func (c *Conn) initSCIONLocked(ctx context.Context) {
+	if c.pconnSCION.Load() != nil {
+		return
+	}
+	sc, err := trySCIONConnect(ctx, c.logf, c.netMon)
+	if err != nil {
+		c.logf("magicsock: SCION not available: %v", err)
+		return
+	}
+	c.logf("magicsock: SCION available, local IA: %s", sc.localIA)
+	c.pconnSCION.Store(sc)
+	go c.refreshSCIONPaths()
+}
+
+// closeSCIONLocked closes the SCION connection if open and sets pconnSCION
+// to nil so that receiveSCION and retrySCIONConnect see it as disconnected.
+// c.mu must be held.
+func (c *Conn) closeSCIONLocked() {
+	if sc := c.pconnSCION.Load(); sc != nil {
+		sc.close()
+		c.pconnSCION.Store(nil)
+	}
+}
+
+// closeSCIONBindLocked sets an immediate read deadline on the SCION socket
+// to unblock receiveSCION, without closing it. Called from connBind.Close.
+// c.mu must be held (via connBind.mu).
+func (c *Conn) closeSCIONBindLocked() {
+	if sc := c.pconnSCION.Load(); sc != nil {
+		// Set an immediate read deadline to unblock receiveSCION.
+		// We don't close the SCION socket here; Conn.Close handles that.
+		sc.conn.SetReadDeadline(time.Now())
+		// Also unblock the dispatcher shim's ReadBatch if present.
+		if sc.shimConn != nil {
+			sc.shimConn.SetReadDeadline(time.Now())
+		}
+	}
+}
diff --git a/wgengine/magicsock/magicsock_scion_omit.go b/wgengine/magicsock/magicsock_scion_omit.go
new file mode 100644
index 0000000000000..aed6b47f7fddb
--- /dev/null
+++ b/wgengine/magicsock/magicsock_scion_omit.go
@@ -0,0 +1,78 @@
+// Copyright (c) Tailscale Inc & contributors
+// SPDX-License-Identifier: BSD-3-Clause
+
+//go:build ts_omit_scion
+
+package magicsock
+
+import (
+	"context"
+	"time"
+
+	wgconn "github.com/tailscale/wireguard-go/conn"
+	"tailscale.com/ipn/ipnstate"
+	"tailscale.com/net/tstun"
+	"tailscale.com/tailcfg"
+	"tailscale.com/tstime/mono"
+)
+
+// Stub types for ts_omit_scion builds.
+
+type scionPathKey uint32
+
+func (k scionPathKey) IsSet() bool { return false }
+
+type scionBatchRW interface{}
+
+type scionConn struct {
+	shimXPC scionBatchRW
+}
+
+func (sc *scionConn) close() error { return nil }
+
+type scionPathInfo struct{}
+
+func (pi *scionPathInfo) String() string { return "" }
+
+type scionAddrKey struct{}
+type scionEndpointState struct{}
+type scionIAKey = uint64
+
+const scionWireMTU = tstun.WireMTU(1280)
+
+// Stub Conn methods.
+
+func (c *Conn) initSCIONLocked(_ context.Context)                                       {}
+func (c *Conn) closeSCIONLocked()                                                        {}
+func (c *Conn) closeSCIONBindLocked()                                                    {}
+func (c *Conn) receiveSCION(_ [][]byte, _ []int, _ []wgconn.Endpoint) (int, error)       { return 0, nil }
+func (c *Conn) receiveSCIONShim(_ [][]byte, _ []int, _ []wgconn.Endpoint) (int, error)  { return 0, nil }
+func (c *Conn) sendSCION(_ scionPathKey, _ []byte) (bool, error)                         { return false, nil }
+func (c *Conn) unregisterSCIONPath(_ scionPathKey)                                       {}
+
+// Stub endpoint methods.
+
+func (de *endpoint) heartbeatSCIONLocked(_ mono.Time)                                    {}
+func (de *endpoint) sendDiscoPingsSCIONLocked(_ mono.Time) bool                          { return false }
+func (de *endpoint) cliPingSCIONLocked(_ mono.Time, _ int, _ *pingResultAndCallback)     {}
+func (de *endpoint) discoPingTimeoutSCIONLocked(_ sentPing)                              {}
+func (de *endpoint) handlePongSCIONLocked(_ epAddr, _ time.Duration, _ mono.Time)        {}
+func (de *endpoint) handlePongPromoteSCIONLocked(_ addrQuality)                          {}
+func (de *endpoint) updateFromNodeSCIONLocked(_ tailcfg.NodeView) []scionPathKey         { return nil }
+func (de *endpoint) stopAndResetSCIONLocked() []scionPathKey                             { return nil }
+func (de *endpoint) sendSCIONData(_ epAddr, _ [][]byte, _ int) error                     { return nil }
+func (de *endpoint) scionAddrStr(e epAddr) string                                       { return e.String() }
+func (de *endpoint) populateSCIONPathsLocked(_ *ipnstate.PeerStatus)                    {}
+
+// SCIONService returns false when SCION is omitted.
+func (c *Conn) SCIONService() (svc tailcfg.Service, ok bool) { return tailcfg.Service{}, false }
+
+func (c *Conn) ReconfigureSCION(_ SCIONConfig)                          {}
+func (c *Conn) SCIONStatus() (connected bool, localIA string)           { return false, "" }
+
+// Stub standalone functions used by betterAddr in endpoint.go.
+
+var preferSCION = func() bool { return false }
+
+func scionPreferenceBonus() int              { return 0 }
+func scionDiversityThreshold() time.Duration { return 0 }
diff --git a/wgengine/magicsock/magicsock_scion_test.go b/wgengine/magicsock/magicsock_scion_test.go
new file mode 100644
index 0000000000000..bf9cf077e1f1d
--- /dev/null
+++ b/wgengine/magicsock/magicsock_scion_test.go
@@ -0,0 +1,2293 @@
+// Copyright (c) Tailscale Inc & contributors
+// SPDX-License-Identifier: BSD-3-Clause
+
+//go:build !ts_omit_scion
+
+package magicsock
+
+import (
+	"context"
+	"encoding/binary"
+	"fmt"
+	"net"
+	"net/netip"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/golang/mock/gomock"
+	"github.com/scionproto/scion/pkg/addr"
+	"github.com/scionproto/scion/pkg/daemon"
+	"github.com/scionproto/scion/pkg/daemon/mock_daemon"
+	"github.com/scionproto/scion/pkg/snet"
+	"github.com/scionproto/scion/pkg/snet/mock_snet"
+	snetpath "github.com/scionproto/scion/pkg/snet/path"
+	"tailscale.com/envknob"
+	"tailscale.com/net/packet"
+	"tailscale.com/net/tstun"
+	"tailscale.com/tailcfg"
+	"tailscale.com/tstime/mono"
+	"tailscale.com/types/key"
+)
+
+func TestScionPathKeyIsSet(t *testing.T) {
+	var zero scionPathKey
+	if zero.IsSet() {
+		t.Error("zero scionPathKey should not be set")
+	}
+	k := scionPathKey(1)
+	if !k.IsSet() {
+		t.Error("non-zero scionPathKey should be set")
+	}
+	k = scionPathKey(42)
+	if !k.IsSet() {
+		t.Error("scionPathKey(42) should be set")
+	}
+}
+
+func TestEpAddrIsSCION(t *testing.T) {
+	tests := []struct {
+		name     string
+		addr     epAddr
+		isSCION  bool
+		isDirect bool
+	}{
+		{
+			name:     "plain UDP",
+			addr:     epAddr{ap: netip.MustParseAddrPort("192.0.2.1:7")},
+			isSCION:  false,
+			isDirect: true,
+		},
+		{
+			name: "with VNI",
+			addr: func() epAddr {
+				e := epAddr{ap: netip.MustParseAddrPort("192.0.2.1:7")}
+				e.vni.Set(7)
+				return e
+			}(),
+			isSCION:  false,
+			isDirect: false,
+		},
+		{
+			name:     "with scionKey",
+			addr:     epAddr{ap: netip.MustParseAddrPort("192.0.2.1:7"), scionKey: 1},
+			isSCION:  true,
+			isDirect: false,
+		},
+		{
+			name:     "DERP magic addr",
+			addr:     epAddr{ap: netip.AddrPortFrom(tailcfg.DerpMagicIPAddr, 1)},
+			isSCION:  false,
+			isDirect: false,
+		},
+		{
+			name:     "zero epAddr",
+			addr:     epAddr{},
+			isSCION:  false,
+			isDirect: false,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := tt.addr.isSCION(); got != tt.isSCION {
+				t.Errorf("isSCION() = %v, want %v", got, tt.isSCION)
+			}
+			if got := tt.addr.isDirect(); got != tt.isDirect {
+				t.Errorf("isDirect() = %v, want %v", got, tt.isDirect)
+			}
+		})
+	}
+}
+
+func TestEpAddrStringWithSCION(t *testing.T) {
+	e := epAddr{ap: netip.MustParseAddrPort("10.0.0.1:41641"), scionKey: 5}
+	got := e.String()
+	want := "10.0.0.1:41641:scion:5"
+	if got != want {
+		t.Errorf("String() = %q, want %q", got, want)
+	}
+
+	// Non-SCION should not include scion label.
+	e2 := epAddr{ap: netip.MustParseAddrPort("10.0.0.1:41641")}
+	got2 := e2.String()
+	want2 := "10.0.0.1:41641"
+	if got2 != want2 {
+		t.Errorf("String() = %q, want %q", got2, want2)
+	}
+}
+
+func TestParseSCIONServiceAddr(t *testing.T) {
+	tests := []struct {
+		name        string
+		description string
+		port        uint16
+		wantIA      addr.IA
+		wantAddr    netip.AddrPort
+		wantErr     bool
+	}{
+		{
+			name:        "valid IPv4 bracketed",
+			description: "1-ff00:0:110,[192.0.2.1]",
+			port:        41641,
+			wantIA:      addr.MustParseIA("1-ff00:0:110"),
+			wantAddr:    netip.MustParseAddrPort("192.0.2.1:41641"),
+		},
+		{
+			name:        "valid IPv6 bracketed",
+			description: "1-ff00:0:110,[2001:db8::1]",
+			port:        12345,
+			wantIA:      addr.MustParseIA("1-ff00:0:110"),
+			wantAddr:    netip.MustParseAddrPort("[2001:db8::1]:12345"),
+		},
+		{
+			name:        "valid IPv4 unbracketed (backward compat)",
+			description: "1-ff00:0:110,192.0.2.1",
+			port:        41641,
+			wantIA:      addr.MustParseIA("1-ff00:0:110"),
+			wantAddr:    netip.MustParseAddrPort("192.0.2.1:41641"),
+		},
+		{
+			name:        "valid IPv6 unbracketed (backward compat)",
+			description: "1-ff00:0:110,2001:db8::1",
+			port:        12345,
+			wantIA:      addr.MustParseIA("1-ff00:0:110"),
+			wantAddr:    netip.MustParseAddrPort("[2001:db8::1]:12345"),
+		},
+		{
+			name:        "missing comma",
+			description: "1-ff00:0:110",
+			port:        41641,
+			wantErr:     true,
+		},
+		{
+			name:        "bad IA",
+			description: "not-an-ia,192.0.2.1",
+			port:        41641,
+			wantErr:     true,
+		},
+		{
+			name:        "bad IP",
+			description: "1-ff00:0:110,not-an-ip",
+			port:        41641,
+			wantErr:     true,
+		},
+		{
+			name:        "empty string",
+			description: "",
+			port:        41641,
+			wantErr:     true,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			ia, hostAddr, err := parseSCIONServiceAddr(tt.description, tt.port)
+			if tt.wantErr {
+				if err == nil {
+					t.Fatalf("expected error, got ia=%v hostAddr=%v", ia, hostAddr)
+				}
+				return
+			}
+			if err != nil {
+				t.Fatalf("unexpected error: %v", err)
+			}
+			if ia != tt.wantIA {
+				t.Errorf("IA = %v, want %v", ia, tt.wantIA)
+			}
+			if hostAddr != tt.wantAddr {
+				t.Errorf("hostAddr = %v, want %v", hostAddr, tt.wantAddr)
+			}
+		})
+	}
+}
+
+func TestSCIONPathRegistry(t *testing.T) {
+	c := &Conn{}
+
+	// Test locking versions (used by callers outside c.mu).
+	pi := &scionPathInfo{
+		peerIA:   addr.MustParseIA("1-ff00:0:111"),
+		hostAddr: netip.MustParseAddrPort("10.0.0.1:41641"),
+	}
+	k := c.registerSCIONPathLocking(pi)
+	if !k.IsSet() {
+		t.Fatal("registered key should be set")
+	}
+
+	got := c.lookupSCIONPathLocking(k)
+	if got != pi {
+		t.Fatalf("lookupSCIONPathLocking(%d) returned wrong path info", k)
+	}
+
+	// Register another.
+	pi2 := &scionPathInfo{
+		peerIA:   addr.MustParseIA("1-ff00:0:112"),
+		hostAddr: netip.MustParseAddrPort("10.0.0.2:41641"),
+	}
+	k2 := c.registerSCIONPathLocking(pi2)
+	if k2 == k {
+		t.Fatal("second key should differ from first")
+	}
+	if c.lookupSCIONPathLocking(k2) != pi2 {
+		t.Fatal("second path not found")
+	}
+
+	// Unregister the first (non-locking, must hold c.mu).
+	c.mu.Lock()
+	c.unregisterSCIONPath(k)
+	c.mu.Unlock()
+
+	if c.lookupSCIONPathLocking(k) != nil {
+		t.Fatal("unregistered path should return nil")
+	}
+	if c.lookupSCIONPathLocking(k2) != pi2 {
+		t.Fatal("second path should still be present after unregistering first")
+	}
+
+	if c.lookupSCIONPathLocking(scionPathKey(9999)) != nil {
+		t.Fatal("non-existent key should return nil")
+	}
+}
+
+func TestBetterAddrSCION(t *testing.T) {
+	const ms = time.Millisecond
+
+	al := func(ipps string, d time.Duration) addrQuality {
+		return addrQuality{epAddr: epAddr{ap: netip.MustParseAddrPort(ipps)}, latency: d}
+	}
+	alSCION := func(ipps string, sk scionPathKey, d time.Duration) addrQuality {
+		return addrQuality{
+			epAddr:  epAddr{ap: netip.MustParseAddrPort(ipps), scionKey: sk},
+			latency: d,
+		}
+	}
+	alSCIONPref := func(ipps string, sk scionPathKey, d time.Duration) addrQuality {
+		return addrQuality{
+			epAddr:         epAddr{ap: netip.MustParseAddrPort(ipps), scionKey: sk},
+			latency:        d,
+			scionPreferred: true,
+		}
+	}
+	avl := func(ipps string, vni uint32, d time.Duration) addrQuality {
+		q := al(ipps, d)
+		q.vni.Set(vni)
+		return q
+	}
+
+	const (
+		publicV4   = "1.2.3.4:555"
+		publicV4_2 = "5.6.7.8:999"
+	)
+
+	tests := []struct {
+		name string
+		a, b addrQuality
+		want bool
+	}{
+		// SCION beats direct at equal latency (default +15 bonus).
+		{
+			name: "SCION beats direct same latency",
+			a:    alSCION(publicV4_2, 1, 100*ms),
+			b:    al(publicV4, 100*ms),
+			want: true,
+		},
+		{
+			name: "direct loses to SCION same latency",
+			a:    al(publicV4, 100*ms),
+			b:    alSCION(publicV4_2, 1, 100*ms),
+			want: false,
+		},
+		// SCION wins over relay (VNI) unconditionally.
+		{
+			name: "SCION beats relay same latency",
+			a:    alSCION(publicV4, 1, 100*ms),
+			b:    avl(publicV4_2, 1, 100*ms),
+			want: true,
+		},
+		{
+			name: "relay loses to SCION same latency",
+			a:    avl(publicV4_2, 1, 100*ms),
+			b:    alSCION(publicV4, 1, 100*ms),
+			want: false,
+		},
+		// scionPreferred bonus (+25 on top of +15) beats direct.
+		{
+			name: "scionPreferred SCION beats direct at similar latency",
+			a:    alSCIONPref(publicV4_2, 1, 100*ms),
+			b:    al(publicV4, 100*ms),
+			want: true,
+		},
+		// Direct wins when significantly faster (SCION only has +15 bonus).
+		{
+			name: "much faster direct beats SCION",
+			a:    alSCION(publicV4_2, 1, 100*ms),
+			b:    al(publicV4, 10*ms),
+			want: false,
+		},
+		// Two SCION paths: lower latency wins.
+		{
+			name: "faster SCION beats slower SCION",
+			a:    alSCION(publicV4, 1, 50*ms),
+			b:    alSCION(publicV4_2, 2, 100*ms),
+			want: true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := betterAddr(tt.a, tt.b)
+			if got != tt.want {
+				t.Errorf("betterAddr(%+v, %+v) = %v; want %v", tt.a, tt.b, got, tt.want)
+			}
+		})
+	}
+}
+
+// newMockPathWithMetadata creates a mock snet.Path that returns the given metadata.
+func newMockPathWithMetadata(ctrl *gomock.Controller, md *snet.PathMetadata) *mock_snet.MockPath {
+	p := mock_snet.NewMockPath(ctrl)
+	p.EXPECT().Metadata().Return(md).AnyTimes()
+	p.EXPECT().UnderlayNextHop().Return(&net.UDPAddr{IP: net.IPv4(127, 0, 0, 1), Port: 30041}).AnyTimes()
+	p.EXPECT().Dataplane().Return(nil).AnyTimes()
+	p.EXPECT().Source().Return(addr.IA(0)).AnyTimes()
+	p.EXPECT().Destination().Return(addr.IA(0)).AnyTimes()
+	return p
+}
+
+func TestTotalPathLatency(t *testing.T) {
+	ctrl := gomock.NewController(t)
+
+	tests := []struct {
+		name string
+		path snet.Path
+		want time.Duration
+	}{
+		{
+			name: "nil metadata",
+			path: newMockPathWithMetadata(ctrl, nil),
+			want: time.Hour,
+		},
+		{
+			name: "empty latency slice",
+			path: newMockPathWithMetadata(ctrl, &snet.PathMetadata{Latency: nil}),
+			want: time.Hour,
+		},
+		{
+			name: "single hop",
+			path: newMockPathWithMetadata(ctrl, &snet.PathMetadata{
+				Latency: []time.Duration{5 * time.Millisecond},
+			}),
+			want: 5 * time.Millisecond,
+		},
+		{
+			name: "multiple hops",
+			path: newMockPathWithMetadata(ctrl, &snet.PathMetadata{
+				Latency: []time.Duration{
+					5 * time.Millisecond,
+					10 * time.Millisecond,
+					3 * time.Millisecond,
+				},
+			}),
+			want: 18 * time.Millisecond,
+		},
+		{
+			name: "with unset latency",
+			path: newMockPathWithMetadata(ctrl, &snet.PathMetadata{
+				Latency: []time.Duration{
+					5 * time.Millisecond,
+					-1, // LatencyUnset
+					3 * time.Millisecond,
+				},
+			}),
+			want: 5*time.Millisecond + scionUnsetHopLatency + 3*time.Millisecond,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := totalPathLatency(tt.path)
+			if got != tt.want {
+				t.Errorf("totalPathLatency() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+
+func TestScionServiceFromPeer(t *testing.T) {
+	tests := []struct {
+		name     string
+		node     *tailcfg.Node
+		wantIA   addr.IA
+		wantAddr netip.AddrPort
+		wantOk   bool
+	}{
+		{
+			name: "peer with SCION service (bracketed IPv4)",
+			node: &tailcfg.Node{
+				ID:  1,
+				Key: testNodeKey(),
+				Hostinfo: (&tailcfg.Hostinfo{
+					Services: []tailcfg.Service{
+						{Proto: tailcfg.TCP, Port: 80},
+						{Proto: tailcfg.SCION, Port: 41641, Description: "1-ff00:0:110,[192.0.2.1]"},
+					},
+				}).View(),
+			},
+			wantIA:   addr.MustParseIA("1-ff00:0:110"),
+			wantAddr: netip.MustParseAddrPort("192.0.2.1:41641"),
+			wantOk:   true,
+		},
+		{
+			name: "peer with SCION service (bracketed IPv6)",
+			node: &tailcfg.Node{
+				ID:  1,
+				Key: testNodeKey(),
+				Hostinfo: (&tailcfg.Hostinfo{
+					Services: []tailcfg.Service{
+						{Proto: tailcfg.SCION, Port: 41641, Description: "1-ff00:0:110,[2001:db8::1]"},
+					},
+				}).View(),
+			},
+			wantIA:   addr.MustParseIA("1-ff00:0:110"),
+			wantAddr: netip.MustParseAddrPort("[2001:db8::1]:41641"),
+			wantOk:   true,
+		},
+		{
+			name: "peer without SCION service",
+			node: &tailcfg.Node{
+				ID:  2,
+				Key: testNodeKey(),
+				Hostinfo: (&tailcfg.Hostinfo{
+					Services: []tailcfg.Service{
+						{Proto: tailcfg.TCP, Port: 80},
+					},
+				}).View(),
+			},
+			wantOk: false,
+		},
+		{
+			name: "peer with invalid SCION description",
+			node: &tailcfg.Node{
+				ID:  3,
+				Key: testNodeKey(),
+				Hostinfo: (&tailcfg.Hostinfo{
+					Services: []tailcfg.Service{
+						{Proto: tailcfg.SCION, Port: 41641, Description: "bad-desc"},
+					},
+				}).View(),
+			},
+			wantOk: false,
+		},
+		{
+			name: "peer with no services",
+			node: &tailcfg.Node{
+				ID:       4,
+				Key:      testNodeKey(),
+				Hostinfo: (&tailcfg.Hostinfo{}).View(),
+			},
+			wantOk: false,
+		},
+		{
+			name: "peer with SCION in peerapi4 description (piggyback, bracketed IPv4)",
+			node: &tailcfg.Node{
+				ID:  5,
+				Key: testNodeKey(),
+				Hostinfo: (&tailcfg.Hostinfo{
+					Services: []tailcfg.Service{
+						{Proto: tailcfg.PeerAPI4, Port: 12345, Description: "scion=1-ff00:0:110,[192.0.2.1]:32766"},
+					},
+				}).View(),
+			},
+			wantIA:   addr.MustParseIA("1-ff00:0:110"),
+			wantAddr: netip.MustParseAddrPort("192.0.2.1:32766"),
+			wantOk:   true,
+		},
+		{
+			name: "peer with SCION piggyback (bracketed IPv6)",
+			node: &tailcfg.Node{
+				ID:  5,
+				Key: testNodeKey(),
+				Hostinfo: (&tailcfg.Hostinfo{
+					Services: []tailcfg.Service{
+						{Proto: tailcfg.PeerAPI4, Port: 12345, Description: "scion=1-ff00:0:110,[2001:db8::1]:32766"},
+					},
+				}).View(),
+			},
+			wantIA:   addr.MustParseIA("1-ff00:0:110"),
+			wantAddr: netip.MustParseAddrPort("[2001:db8::1]:32766"),
+			wantOk:   true,
+		},
+		{
+			name: "peer with SCION piggyback (unbracketed IPv4, backward compat)",
+			node: &tailcfg.Node{
+				ID:  5,
+				Key: testNodeKey(),
+				Hostinfo: (&tailcfg.Hostinfo{
+					Services: []tailcfg.Service{
+						{Proto: tailcfg.PeerAPI4, Port: 12345, Description: "scion=1-ff00:0:110,192.0.2.1:32766"},
+					},
+				}).View(),
+			},
+			wantIA:   addr.MustParseIA("1-ff00:0:110"),
+			wantAddr: netip.MustParseAddrPort("192.0.2.1:32766"),
+			wantOk:   true,
+		},
+		{
+			name: "peer with bad SCION piggyback",
+			node: &tailcfg.Node{
+				ID:  6,
+				Key: testNodeKey(),
+				Hostinfo: (&tailcfg.Hostinfo{
+					Services: []tailcfg.Service{
+						{Proto: tailcfg.PeerAPI4, Port: 12345, Description: "scion=bad-data"},
+					},
+				}).View(),
+			},
+			wantOk: false,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			nv := tt.node.View()
+			ia, hostAddr, ok := scionServiceFromPeer(nv)
+			if ok != tt.wantOk {
+				t.Fatalf("ok = %v, want %v", ok, tt.wantOk)
+			}
+			if !tt.wantOk {
+				return
+			}
+			if ia != tt.wantIA {
+				t.Errorf("IA = %v, want %v", ia, tt.wantIA)
+			}
+			if hostAddr != tt.wantAddr {
+				t.Errorf("hostAddr = %v, want %v", hostAddr, tt.wantAddr)
+			}
+		})
+	}
+}
+
+func TestIsKnownServiceProtoSCION(t *testing.T) {
+	if !tailcfg.IsKnownServiceProto(tailcfg.SCION) {
+		t.Error("SCION should be a known service proto")
+	}
+}
+
+func TestEpAddrComparability(t *testing.T) {
+	// Verify that epAddr with scionKey is still comparable (usable as map key).
+	a := epAddr{ap: netip.MustParseAddrPort("10.0.0.1:41641"), scionKey: 1}
+	b := epAddr{ap: netip.MustParseAddrPort("10.0.0.1:41641"), scionKey: 1}
+	c := epAddr{ap: netip.MustParseAddrPort("10.0.0.1:41641"), scionKey: 2}
+
+	if a != b {
+		t.Error("identical epAddr values should be equal")
+	}
+	if a == c {
+		t.Error("epAddr values with different scionKey should not be equal")
+	}
+
+	// Verify usable as map key.
+	m := map[epAddr]bool{a: true}
+	if !m[b] {
+		t.Error("identical epAddr should be found in map")
+	}
+	if m[c] {
+		t.Error("different scionKey epAddr should not be found in map")
+	}
+}
+
+func TestBetterAddrSCIONWithExistingCases(t *testing.T) {
+	// Verify that adding SCION support doesn't break existing betterAddr
+	// behavior for non-SCION addresses. These are a subset of cases from
+	// the existing TestBetterAddr.
+	const ms = time.Millisecond
+	al := func(ipps string, d time.Duration) addrQuality {
+		return addrQuality{epAddr: epAddr{ap: netip.MustParseAddrPort(ipps)}, latency: d}
+	}
+	almtu := func(ipps string, d time.Duration, mtu tstun.WireMTU) addrQuality {
+		return addrQuality{epAddr: epAddr{ap: netip.MustParseAddrPort(ipps)}, latency: d, wireMTU: mtu}
+	}
+	avl := func(ipps string, vni uint32, d time.Duration) addrQuality {
+		q := al(ipps, d)
+		q.vni.Set(vni)
+		return q
+	}
+	zero := addrQuality{}
+
+	tests := []struct {
+		a, b addrQuality
+		want bool
+	}{
+		{a: zero, b: zero, want: false},
+		{a: al("1.2.3.4:555", 5*ms), b: zero, want: true},
+		{a: zero, b: al("1.2.3.4:555", 5*ms), want: false},
+		{a: al("1.2.3.4:555", 5*ms), b: al("5.6.7.8:999", 10*ms), want: true},
+		// Private IP preference still works.
+		{a: al("10.0.0.2:123", 100*ms), b: al("1.2.3.4:555", 91*ms), want: true},
+		// Geneve preference still works.
+		{a: al("1.2.3.4:555", 100*ms), b: avl("1.2.3.4:555", 1, 100*ms), want: true},
+		{a: avl("1.2.3.4:555", 1, 100*ms), b: al("1.2.3.4:555", 100*ms), want: false},
+		// MTU preference for same address still works.
+		{a: almtu("1.2.3.4:555", 30*ms, 1500), b: almtu("1.2.3.4:555", 30*ms, 0), want: true},
+	}
+	for i, tt := range tests {
+		got := betterAddr(tt.a, tt.b)
+		if got != tt.want {
+			t.Errorf("[%d] betterAddr(%+v, %+v) = %v; want %v", i, tt.a, tt.b, got, tt.want)
+		}
+	}
+}
+
+func TestSCIONPathRegistryReverseIndex(t *testing.T) {
+	c := &Conn{}
+
+	pi := &scionPathInfo{
+		peerIA:   addr.MustParseIA("1-ff00:0:111"),
+		hostAddr: netip.MustParseAddrPort("10.0.0.1:41641"),
+	}
+	k := c.registerSCIONPathLocking(pi)
+
+	// Set as active path so the reverse index is populated.
+	c.mu.Lock()
+	c.setActiveSCIONPath(pi.peerIA, pi.hostAddr, k)
+	c.mu.Unlock()
+
+	// Reverse lookup should find the key.
+	got := c.scionKeyForAddr(pi.peerIA, pi.hostAddr)
+	if got != k {
+		t.Errorf("scionKeyForAddr returned %d, want %d", got, k)
+	}
+
+	// Different address should not match.
+	got2 := c.scionKeyForAddr(pi.peerIA, netip.MustParseAddrPort("10.0.0.2:41641"))
+	if got2.IsSet() {
+		t.Error("scionKeyForAddr should return zero for unknown address")
+	}
+
+	// Unregister should remove from reverse index.
+	c.mu.Lock()
+	c.unregisterSCIONPath(k)
+	c.mu.Unlock()
+
+	got3 := c.scionKeyForAddr(pi.peerIA, pi.hostAddr)
+	if got3.IsSet() {
+		t.Error("scionKeyForAddr should return zero after unregister")
+	}
+}
+
+func TestSCIONEndpointState(t *testing.T) {
+	ia := addr.MustParseIA("1-ff00:0:110")
+	hostAddr := netip.MustParseAddrPort("192.0.2.1:41641")
+
+	pk := scionPathKey(5)
+	st := &scionEndpointState{
+		peerIA:     ia,
+		hostAddr:   hostAddr,
+		paths:      map[scionPathKey]*scionPathProbeState{pk: {}},
+		activePath: pk,
+	}
+
+	if st.peerIA != ia {
+		t.Errorf("peerIA = %v, want %v", st.peerIA, ia)
+	}
+	if st.hostAddr != hostAddr {
+		t.Errorf("hostAddr = %v, want %v", st.hostAddr, hostAddr)
+	}
+	if !st.activePath.IsSet() {
+		t.Error("activePath should be set")
+	}
+	if len(st.paths) != 1 {
+		t.Errorf("paths count = %d, want 1", len(st.paths))
+	}
+}
+
+func TestSendSCIONBatchNoConn(t *testing.T) {
+	c := &Conn{}
+
+	ep := epAddr{
+		ap:       netip.MustParseAddrPort("10.0.0.1:41641"),
+		scionKey: 1,
+	}
+	_, err := c.sendSCIONBatch(ep, [][]byte{{0x01}}, 0)
+	if err != errNoSCION {
+		t.Errorf("sendSCIONBatch with nil pconnSCION: got err=%v, want %v", err, errNoSCION)
+	}
+}
+
+func TestSendSCIONNoConn(t *testing.T) {
+	c := &Conn{}
+
+	_, err := c.sendSCION(scionPathKey(1), []byte{0x01})
+	if err != errNoSCION {
+		t.Errorf("sendSCION with nil pconnSCION: got err=%v, want %v", err, errNoSCION)
+	}
+}
+
+func TestSCIONPathInfoMutexSafety(t *testing.T) {
+	pi := &scionPathInfo{
+		peerIA:   addr.MustParseIA("1-ff00:0:110"),
+		hostAddr: netip.MustParseAddrPort("10.0.0.1:41641"),
+		expiry:   time.Now().Add(time.Hour),
+	}
+
+	// Verify concurrent access is safe.
+	done := make(chan struct{})
+	go func() {
+		defer close(done)
+		for i := 0; i < 100; i++ {
+			pi.mu.Lock()
+			_ = pi.peerIA
+			_ = pi.hostAddr
+			_ = pi.expiry
+			pi.mu.Unlock()
+		}
+	}()
+	for i := 0; i < 100; i++ {
+		pi.mu.Lock()
+		pi.expiry = time.Now().Add(time.Duration(i) * time.Minute)
+		pi.mu.Unlock()
+	}
+	<-done
+}
+
+func TestScionListenPort(t *testing.T) {
+	tests := []struct {
+		name   string
+		envVal string
+		want   uint16
+	}{
+		{"default auto-select", "", 0},
+		{"valid port", "31337", 31337},
+		{"min port", "30000", 30000},
+		{"max port", "32767", 32767},
+		{"below range", "29999", 29999},   // scionListenPort only parses; range validation is in trySCIONConnect
+		{"above range", "32768", 32768},   // same: validated against daemon port range later
+		{"non-numeric", "abc", 0},
+		{"wireguard port", "41641", 41641}, // any valid port is accepted at parse time
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if tt.envVal != "" {
+				envknob.Setenv("TS_SCION_PORT", tt.envVal)
+				t.Cleanup(func() { envknob.Setenv("TS_SCION_PORT", "") })
+			}
+			got := scionListenPort()
+			if got != tt.want {
+				t.Errorf("scionListenPort() = %d, want %d", got, tt.want)
+			}
+		})
+	}
+}
+
+func TestSCIONDiscoRXPath(t *testing.T) {
+	if discoRXPathSCION != "SCION" {
+		t.Errorf("discoRXPathSCION = %q, want %q", discoRXPathSCION, "SCION")
+	}
+}
+
+// testNodeKey returns a new NodePublic for test node construction.
+func testNodeKey() key.NodePublic { return key.NewNode().Public() }
+
+func TestDiscoverSCIONPaths(t *testing.T) {
+	ctrl := gomock.NewController(t)
+	mockDaemon := mock_daemon.NewMockConnector(ctrl)
+
+	localIA := addr.MustParseIA("1-ff00:0:110")
+	peerIA := addr.MustParseIA("1-ff00:0:111")
+	hostAddr := netip.MustParseAddrPort("10.0.0.1:41641")
+
+	t.Run("picks lowest latency path", func(t *testing.T) {
+		// Create three mock paths with different latencies.
+		slowPath := newMockPathWithMetadata(ctrl, &snet.PathMetadata{
+			Latency: []time.Duration{50 * time.Millisecond, 50 * time.Millisecond},
+			Expiry:  time.Now().Add(time.Hour),
+		})
+		fastPath := newMockPathWithMetadata(ctrl, &snet.PathMetadata{
+			Latency: []time.Duration{5 * time.Millisecond},
+			Expiry:  time.Now().Add(time.Hour),
+		})
+		mediumPath := newMockPathWithMetadata(ctrl, &snet.PathMetadata{
+			Latency: []time.Duration{20 * time.Millisecond, 10 * time.Millisecond},
+			Expiry:  time.Now().Add(time.Hour),
+		})
+
+		mockDaemon.EXPECT().Paths(gomock.Any(), peerIA, localIA, daemon.PathReqFlags{Refresh: false}).
+			Return([]snet.Path{slowPath, fastPath, mediumPath}, nil)
+
+		c := &Conn{}
+		c.pconnSCION.Store(&scionConn{daemon: mockDaemon, localIA: localIA})
+
+		keys, err := c.discoverSCIONPaths(context.Background(), peerIA, hostAddr)
+		if err != nil {
+			t.Fatalf("unexpected error: %v", err)
+		}
+		if len(keys) == 0 {
+			t.Fatal("returned keys should not be empty")
+		}
+		// All 3 paths should be registered (deduped by fingerprint, but mock
+		// paths have no metadata for fingerprinting so they're all unique).
+		if len(keys) != 3 {
+			t.Fatalf("expected 3 keys, got %d", len(keys))
+		}
+
+		// First key should be the lowest-latency path (fast one, 5ms).
+		pi := c.lookupSCIONPathLocking(keys[0])
+		if pi == nil {
+			t.Fatal("path info not found in registry")
+		}
+		if pi.peerIA != peerIA {
+			t.Errorf("peerIA = %v, want %v", pi.peerIA, peerIA)
+		}
+		if pi.hostAddr != hostAddr {
+			t.Errorf("hostAddr = %v, want %v", pi.hostAddr, hostAddr)
+		}
+		// The first (active) path should be the fast one (5ms).
+		if pi.path != fastPath {
+			t.Error("first key should be the lowest-latency path")
+		}
+	})
+
+	t.Run("no paths available", func(t *testing.T) {
+		mockDaemon.EXPECT().Paths(gomock.Any(), peerIA, localIA, daemon.PathReqFlags{Refresh: false}).
+			Return(nil, nil)
+
+		c := &Conn{}
+		c.pconnSCION.Store(&scionConn{daemon: mockDaemon, localIA: localIA})
+
+		_, err := c.discoverSCIONPaths(context.Background(), peerIA, hostAddr)
+		if err == nil {
+			t.Fatal("expected error for no paths")
+		}
+	})
+
+	t.Run("daemon error", func(t *testing.T) {
+		mockDaemon.EXPECT().Paths(gomock.Any(), peerIA, localIA, daemon.PathReqFlags{Refresh: false}).
+			Return(nil, fmt.Errorf("daemon unavailable"))
+
+		c := &Conn{}
+		c.pconnSCION.Store(&scionConn{daemon: mockDaemon, localIA: localIA})
+
+		_, err := c.discoverSCIONPaths(context.Background(), peerIA, hostAddr)
+		if err == nil {
+			t.Fatal("expected error for daemon failure")
+		}
+	})
+
+	t.Run("nil pconnSCION", func(t *testing.T) {
+		c := &Conn{}
+		_, err := c.discoverSCIONPaths(context.Background(), peerIA, hostAddr)
+		if err != errNoSCION {
+			t.Errorf("expected errNoSCION, got %v", err)
+		}
+	})
+
+	t.Run("single path with no metadata", func(t *testing.T) {
+		noMetaPath := newMockPathWithMetadata(ctrl, nil)
+		mockDaemon.EXPECT().Paths(gomock.Any(), peerIA, localIA, daemon.PathReqFlags{Refresh: false}).
+			Return([]snet.Path{noMetaPath}, nil)
+
+		c := &Conn{}
+		c.pconnSCION.Store(&scionConn{daemon: mockDaemon, localIA: localIA})
+
+		keys, err := c.discoverSCIONPaths(context.Background(), peerIA, hostAddr)
+		if err != nil {
+			t.Fatalf("unexpected error: %v", err)
+		}
+		if len(keys) == 0 {
+			t.Fatal("returned keys should not be empty")
+		}
+		pi := c.lookupSCIONPathLocking(keys[0])
+		if pi == nil {
+			t.Fatal("path info not found")
+		}
+		if !pi.expiry.IsZero() {
+			t.Errorf("expiry should be zero for nil metadata, got %v", pi.expiry)
+		}
+	})
+}
+
+func TestRefreshSCIONPathsOnce(t *testing.T) {
+	ctrl := gomock.NewController(t)
+	mockDaemon := mock_daemon.NewMockConnector(ctrl)
+
+	localIA := addr.MustParseIA("1-ff00:0:110")
+	peerIA := addr.MustParseIA("1-ff00:0:111")
+
+	t.Run("refreshes expiring path", func(t *testing.T) {
+		newExpiry := time.Now().Add(2 * time.Hour)
+		newPath := newMockPathWithMetadata(ctrl, &snet.PathMetadata{
+			Latency: []time.Duration{3 * time.Millisecond},
+			Expiry:  newExpiry,
+		})
+
+		mockDaemon.EXPECT().Paths(gomock.Any(), peerIA, localIA, daemon.PathReqFlags{Refresh: true}).
+			Return([]snet.Path{newPath}, nil)
+
+		ctx, cancel := context.WithCancel(context.Background())
+		defer cancel()
+
+		c := &Conn{
+			connCtx: ctx,
+		}
+		c.logf = t.Logf
+		c.pconnSCION.Store(&scionConn{daemon: mockDaemon, localIA: localIA})
+
+		// Register a path that's about to expire (30s from now, within the 1-min refresh window).
+		pi := &scionPathInfo{
+			peerIA:   peerIA,
+			hostAddr: netip.MustParseAddrPort("10.0.0.1:41641"),
+			expiry:   time.Now().Add(30 * time.Second),
+		}
+		k := c.registerSCIONPathLocking(pi)
+
+		c.refreshSCIONPathsOnce()
+
+		// Verify the path was updated.
+		got := c.lookupSCIONPathLocking(k)
+		got.mu.Lock()
+		gotPath := got.path
+		gotExpiry := got.expiry
+		got.mu.Unlock()
+
+		if gotPath != newPath {
+			t.Error("path should have been refreshed to new path")
+		}
+		if !gotExpiry.Equal(newExpiry) {
+			t.Errorf("expiry = %v, want %v", gotExpiry, newExpiry)
+		}
+	})
+
+	t.Run("skips non-expiring path", func(t *testing.T) {
+		// No daemon calls expected — the path doesn't need refresh.
+		ctx, cancel := context.WithCancel(context.Background())
+		defer cancel()
+
+		c := &Conn{
+			connCtx: ctx,
+		}
+		c.logf = t.Logf
+		c.pconnSCION.Store(&scionConn{daemon: mockDaemon, localIA: localIA})
+
+		// Register a path that's far from expiry.
+		pi := &scionPathInfo{
+			peerIA:   peerIA,
+			hostAddr: netip.MustParseAddrPort("10.0.0.1:41641"),
+			expiry:   time.Now().Add(2 * time.Hour),
+		}
+		c.registerSCIONPathLocking(pi)
+
+		// Should not call daemon.Paths since path doesn't need refresh.
+		c.refreshSCIONPathsOnce()
+	})
+
+	t.Run("handles daemon failure gracefully", func(t *testing.T) {
+		mockDaemon.EXPECT().Paths(gomock.Any(), peerIA, localIA, daemon.PathReqFlags{Refresh: true}).
+			Return(nil, fmt.Errorf("daemon unreachable"))
+
+		ctx, cancel := context.WithCancel(context.Background())
+		defer cancel()
+
+		c := &Conn{
+			connCtx: ctx,
+		}
+		c.logf = t.Logf
+		c.pconnSCION.Store(&scionConn{daemon: mockDaemon, localIA: localIA})
+
+		oldPath := newMockPathWithMetadata(ctrl, &snet.PathMetadata{
+			Latency: []time.Duration{10 * time.Millisecond},
+		})
+
+		// Register an expiring path.
+		pi := &scionPathInfo{
+			peerIA:   peerIA,
+			hostAddr: netip.MustParseAddrPort("10.0.0.1:41641"),
+			path:     oldPath,
+			expiry:   time.Now().Add(30 * time.Second),
+		}
+		k := c.registerSCIONPathLocking(pi)
+
+		c.refreshSCIONPathsOnce()
+
+		// Path should remain unchanged after daemon failure.
+		got := c.lookupSCIONPathLocking(k)
+		got.mu.Lock()
+		gotPath := got.path
+		got.mu.Unlock()
+
+		if gotPath != oldPath {
+			t.Error("path should not have changed after daemon failure")
+		}
+	})
+
+	t.Run("picks best path among refreshed results", func(t *testing.T) {
+		slowPath := newMockPathWithMetadata(ctrl, &snet.PathMetadata{
+			Latency: []time.Duration{100 * time.Millisecond},
+			Expiry:  time.Now().Add(2 * time.Hour),
+		})
+		fastPath := newMockPathWithMetadata(ctrl, &snet.PathMetadata{
+			Latency: []time.Duration{2 * time.Millisecond},
+			Expiry:  time.Now().Add(2 * time.Hour),
+		})
+
+		mockDaemon.EXPECT().Paths(gomock.Any(), peerIA, localIA, daemon.PathReqFlags{Refresh: true}).
+			Return([]snet.Path{slowPath, fastPath}, nil)
+
+		ctx, cancel := context.WithCancel(context.Background())
+		defer cancel()
+
+		c := &Conn{
+			connCtx: ctx,
+		}
+		c.logf = t.Logf
+		c.pconnSCION.Store(&scionConn{daemon: mockDaemon, localIA: localIA})
+
+		pi := &scionPathInfo{
+			peerIA:   peerIA,
+			hostAddr: netip.MustParseAddrPort("10.0.0.1:41641"),
+			expiry:   time.Now().Add(30 * time.Second), // about to expire
+		}
+		k := c.registerSCIONPathLocking(pi)
+
+		c.refreshSCIONPathsOnce()
+
+		got := c.lookupSCIONPathLocking(k)
+		got.mu.Lock()
+		gotPath := got.path
+		got.mu.Unlock()
+
+		if gotPath != fastPath {
+			t.Error("should have selected lowest-latency path during refresh")
+		}
+	})
+}
+
+// Verify that the scionPathKey field doesn't break epAddr's use in
+// packet.VirtualNetworkID interactions.
+func TestEpAddrSCIONAndVNIMutualExclusion(t *testing.T) {
+	// SCION and VNI shouldn't be set simultaneously in practice,
+	// but verify the type behavior is correct.
+	var vni packet.VirtualNetworkID
+	vni.Set(42)
+
+	both := epAddr{
+		ap:       netip.MustParseAddrPort("1.2.3.4:555"),
+		vni:      vni,
+		scionKey: 1,
+	}
+	// With both set, it's neither direct nor SCION-only.
+	if both.isDirect() {
+		t.Error("epAddr with both VNI and scionKey should not be direct")
+	}
+	if !both.isSCION() {
+		t.Error("epAddr with scionKey should report isSCION")
+	}
+	// String should show SCION since scionKey takes precedence in String().
+	got := both.String()
+	if got != "1.2.3.4:555:scion:1" {
+		t.Errorf("String() = %q, want SCION format", got)
+	}
+}
+
+func TestStopAndResetCleansSCIONPath(t *testing.T) {
+	c := &Conn{}
+	c.logf = t.Logf
+
+	pi := &scionPathInfo{
+		peerIA:   addr.MustParseIA("1-ff00:0:111"),
+		hostAddr: netip.MustParseAddrPort("10.0.0.1:41641"),
+	}
+	k := c.registerSCIONPathLocking(pi)
+
+	de := &endpoint{c: c}
+	de.scionState = &scionEndpointState{
+		peerIA:     pi.peerIA,
+		hostAddr:   pi.hostAddr,
+		paths:      map[scionPathKey]*scionPathProbeState{k: {}},
+		activePath: k,
+	}
+
+	// stopAndReset requires c.mu to be held (all production callers hold it).
+	c.mu.Lock()
+	de.stopAndReset()
+	c.mu.Unlock()
+
+	if de.scionState != nil {
+		t.Error("scionState should be nil after stopAndReset")
+	}
+	if c.lookupSCIONPathLocking(k) != nil {
+		t.Error("SCION path should be removed from registry after stopAndReset")
+	}
+}
+
+func TestNoteRecvActivitySCIONTrustRefresh(t *testing.T) {
+	c := &Conn{}
+	de := &endpoint{c: c}
+	de.heartbeatDisabled = true
+
+	scionAddr := epAddr{ap: netip.MustParseAddrPort("127.0.0.1:32766"), scionKey: 2}
+	plainAddr := epAddr{ap: netip.MustParseAddrPort("127.0.0.1:32766")}
+
+	now := mono.Now()
+	de.bestAddr.epAddr = scionAddr
+	de.bestAddrAt = now
+
+	// WireGuard data arrives with plain addr (no scionKey).
+	de.noteRecvActivity(plainAddr, now)
+
+	de.mu.Lock()
+	trust := de.trustBestAddrUntil
+	de.mu.Unlock()
+
+	if trust == 0 {
+		t.Error("trustBestAddrUntil should be extended for SCION bestAddr when receiving plain addr data")
+	}
+}
+
+func TestSendSCIONBatchExpiredPath(t *testing.T) {
+	c := &Conn{}
+	c.pconnSCION.Store(&scionConn{})
+
+	pi := &scionPathInfo{
+		peerIA:   addr.MustParseIA("1-ff00:0:111"),
+		hostAddr: netip.MustParseAddrPort("10.0.0.1:41641"),
+		expiry:   time.Now().Add(-1 * time.Hour), // expired
+	}
+	k := c.registerSCIONPathLocking(pi)
+
+	ep := epAddr{ap: netip.MustParseAddrPort("10.0.0.1:41641"), scionKey: k}
+	_, err := c.sendSCIONBatch(ep, [][]byte{{0x01}}, 0)
+	if err == nil {
+		t.Fatal("expected error for expired path")
+	}
+	if !strings.Contains(err.Error(), "expired") {
+		t.Errorf("error should mention 'expired', got: %v", err)
+	}
+}
+
+func TestSendSCIONExpiredPath(t *testing.T) {
+	c := &Conn{}
+	c.pconnSCION.Store(&scionConn{})
+
+	pi := &scionPathInfo{
+		peerIA:   addr.MustParseIA("1-ff00:0:111"),
+		hostAddr: netip.MustParseAddrPort("10.0.0.1:41641"),
+		expiry:   time.Now().Add(-1 * time.Hour), // expired
+	}
+	k := c.registerSCIONPathLocking(pi)
+
+	_, err := c.sendSCION(k, []byte{0x01})
+	if err == nil {
+		t.Fatal("expected error for expired path")
+	}
+	if !strings.Contains(err.Error(), "expired") {
+		t.Errorf("error should mention 'expired', got: %v", err)
+	}
+}
+
+// TestSCIONPseudoHeaderPartial verifies the partial checksum computation
+// matches the reference SCION implementation for known inputs.
+func TestSCIONPseudoHeaderPartial(t *testing.T) {
+	srcIA := addr.MustParseIA("1-ff00:0:110")
+	dstIA := addr.MustParseIA("1-ff00:0:111")
+	srcIP := netip.MustParseAddr("127.0.0.1")
+	dstIP := netip.MustParseAddr("127.0.0.1")
+
+	partial := scionPseudoHeaderPartial(srcIA, dstIA, srcIP, dstIP)
+
+	// Verify by computing the same checksum manually:
+	// srcIA = 0x0001ff0000000110, dstIA = 0x0001ff0000000111
+	// srcAddr = 127.0.0.1 = [0x7f, 0x00, 0x00, 0x01]
+	// dstAddr = 127.0.0.1 = [0x7f, 0x00, 0x00, 0x01]
+	// protocol = 17
+
+	var expected uint32
+	// srcIA bytes: 00 01 ff 00 00 00 01 10
+	expected += 0x0001 + 0xff00 + 0x0000 + 0x0110
+	// dstIA bytes: 00 01 ff 00 00 00 01 11
+	expected += 0x0001 + 0xff00 + 0x0000 + 0x0111
+	// srcAddr: 7f 00 00 01
+	expected += 0x7f00 + 0x0001
+	// dstAddr: 7f 00 00 01
+	expected += 0x7f00 + 0x0001
+	// protocol
+	expected += 17
+
+	if partial != expected {
+		t.Errorf("scionPseudoHeaderPartial = %d, want %d", partial, expected)
+	}
+}
+
+// TestSCIONPseudoHeaderPartialIPv6 verifies checksum with IPv6 addresses.
+func TestSCIONPseudoHeaderPartialIPv6(t *testing.T) {
+	srcIA := addr.MustParseIA("1-ff00:0:110")
+	dstIA := addr.MustParseIA("1-ff00:0:111")
+	srcIP := netip.MustParseAddr("::1")
+	dstIP := netip.MustParseAddr("fd00::1")
+
+	partial := scionPseudoHeaderPartial(srcIA, dstIA, srcIP, dstIP)
+	if partial == 0 {
+		t.Fatal("checksum should not be zero")
+	}
+
+	// Verify IPv6 addrs are 16 bytes each.
+	// ::1 = 00...01, fd00::1 = fd 00 00...01
+	var expected uint32
+	// IAs
+	expected += 0x0001 + 0xff00 + 0x0000 + 0x0110
+	expected += 0x0001 + 0xff00 + 0x0000 + 0x0111
+	// srcIP ::1 = all zeros except last byte
+	expected += 0x0001
+	// dstIP fd00::1
+	expected += 0xfd00 + 0x0001
+	expected += 17
+
+	if partial != expected {
+		t.Errorf("scionPseudoHeaderPartial(IPv6) = %d, want %d", partial, expected)
+	}
+}
+
+// TestSCIONFinishChecksum verifies the full checksum computation matches
+// the reference SCION implementation by comparing against a packet
+// serialized with snet.Packet.Serialize().
+func TestSCIONFinishChecksum(t *testing.T) {
+	srcIA := addr.MustParseIA("1-ff00:0:110")
+	dstIA := addr.MustParseIA("1-ff00:0:111")
+	srcIP := netip.MustParseAddr("127.0.0.1")
+	dstIP := netip.MustParseAddr("127.0.0.1")
+	srcPort := uint16(32766)
+	dstPort := uint16(32766)
+	payload := []byte("Hello, SCION fast path!")
+
+	// Build the packet using snet's reference serializer.
+	pkt := &snet.Packet{
+		PacketInfo: snet.PacketInfo{
+			Destination: snet.SCIONAddress{IA: dstIA, Host: addr.HostIP(dstIP)},
+			Source:      snet.SCIONAddress{IA: srcIA, Host: addr.HostIP(srcIP)},
+			Path:        snetpath.Empty{},
+			Payload: snet.UDPPayload{
+				SrcPort: srcPort,
+				DstPort: dstPort,
+				Payload: payload,
+			},
+		},
+	}
+	if err := pkt.Serialize(); err != nil {
+		t.Fatalf("snet.Packet.Serialize: %v", err)
+	}
+
+	// Extract the reference checksum from the serialized packet.
+	// The UDP header is the last 8 bytes before the payload.
+	udpOffset := len(pkt.Bytes) - 8 - len(payload)
+	refChecksum := binary.BigEndian.Uint16(pkt.Bytes[udpOffset+6:])
+
+	// Now compute it using our fast-path functions.
+	partial := scionPseudoHeaderPartial(srcIA, dstIA, srcIP, dstIP)
+
+	// Build the upper layer: UDP header (8 bytes) + payload
+	upperLayer := make([]byte, 8+len(payload))
+	binary.BigEndian.PutUint16(upperLayer[0:], srcPort)
+	binary.BigEndian.PutUint16(upperLayer[2:], dstPort)
+	binary.BigEndian.PutUint16(upperLayer[4:], uint16(8+len(payload)))
+	// checksum field = 0 for computation
+	copy(upperLayer[8:], payload)
+
+	fastChecksum := scionFinishChecksum(partial, upperLayer)
+
+	if fastChecksum != refChecksum {
+		t.Errorf("fast-path checksum = 0x%04x, reference = 0x%04x", fastChecksum, refChecksum)
+	}
+}
+
+// TestSCIONFinishChecksumEmptyPayload verifies checksum with empty payload.
+func TestSCIONFinishChecksumEmptyPayload(t *testing.T) {
+	srcIA := addr.MustParseIA("1-ff00:0:110")
+	dstIA := addr.MustParseIA("1-ff00:0:111")
+	srcIP := netip.MustParseAddr("127.0.0.1")
+	dstIP := netip.MustParseAddr("127.0.0.1")
+
+	pkt := &snet.Packet{
+		PacketInfo: snet.PacketInfo{
+			Destination: snet.SCIONAddress{IA: dstIA, Host: addr.HostIP(dstIP)},
+			Source:      snet.SCIONAddress{IA: srcIA, Host: addr.HostIP(srcIP)},
+			Path:        snetpath.Empty{},
+			Payload: snet.UDPPayload{
+				SrcPort: 1000,
+				DstPort: 2000,
+				Payload: nil,
+			},
+		},
+	}
+	if err := pkt.Serialize(); err != nil {
+		t.Fatalf("snet.Packet.Serialize: %v", err)
+	}
+
+	// UDP header is the last 8 bytes (no payload).
+	udpOffset := len(pkt.Bytes) - 8
+	refChecksum := binary.BigEndian.Uint16(pkt.Bytes[udpOffset+6:])
+
+	partial := scionPseudoHeaderPartial(srcIA, dstIA, srcIP, dstIP)
+	upperLayer := make([]byte, 8)
+	binary.BigEndian.PutUint16(upperLayer[0:], 1000)
+	binary.BigEndian.PutUint16(upperLayer[2:], 2000)
+	binary.BigEndian.PutUint16(upperLayer[4:], 8)
+
+	fastChecksum := scionFinishChecksum(partial, upperLayer)
+
+	if fastChecksum != refChecksum {
+		t.Errorf("fast-path checksum (empty) = 0x%04x, reference = 0x%04x", fastChecksum, refChecksum)
+	}
+}
+
+// TestSCIONFinishChecksumOddPayload verifies correct handling of odd-length payloads.
+func TestSCIONFinishChecksumOddPayload(t *testing.T) {
+	srcIA := addr.MustParseIA("1-ff00:0:110")
+	dstIA := addr.MustParseIA("1-ff00:0:111")
+	srcIP := netip.MustParseAddr("127.0.0.1")
+	dstIP := netip.MustParseAddr("10.0.0.1")
+	payload := []byte("ABC") // 3 bytes, odd
+
+	pkt := &snet.Packet{
+		PacketInfo: snet.PacketInfo{
+			Destination: snet.SCIONAddress{IA: dstIA, Host: addr.HostIP(dstIP)},
+			Source:      snet.SCIONAddress{IA: srcIA, Host: addr.HostIP(srcIP)},
+			Path:        snetpath.Empty{},
+			Payload: snet.UDPPayload{
+				SrcPort: 5000,
+				DstPort: 6000,
+				Payload: payload,
+			},
+		},
+	}
+	if err := pkt.Serialize(); err != nil {
+		t.Fatalf("snet.Packet.Serialize: %v", err)
+	}
+
+	udpOffset := len(pkt.Bytes) - 8 - len(payload)
+	refChecksum := binary.BigEndian.Uint16(pkt.Bytes[udpOffset+6:])
+
+	partial := scionPseudoHeaderPartial(srcIA, dstIA, srcIP, dstIP)
+	upperLayer := make([]byte, 8+len(payload))
+	binary.BigEndian.PutUint16(upperLayer[0:], 5000)
+	binary.BigEndian.PutUint16(upperLayer[2:], 6000)
+	binary.BigEndian.PutUint16(upperLayer[4:], uint16(8+len(payload)))
+	copy(upperLayer[8:], payload)
+
+	fastChecksum := scionFinishChecksum(partial, upperLayer)
+
+	if fastChecksum != refChecksum {
+		t.Errorf("fast-path checksum (odd) = 0x%04x, reference = 0x%04x", fastChecksum, refChecksum)
+	}
+}
+
+// TestBuildSCIONFastPath verifies that buildSCIONFastPath produces a template
+// that matches the reference serializer output for the same parameters.
+func TestBuildSCIONFastPath(t *testing.T) {
+	srcIA := addr.MustParseIA("1-ff00:0:110")
+	dstIA := addr.MustParseIA("1-ff00:0:111")
+	srcIP := netip.MustParseAddr("127.0.0.1")
+	dstIP := netip.MustParseAddr("127.0.0.1")
+	srcPort := uint16(32766)
+	dstPort := uint16(32766)
+
+	sc := &scionConn{
+		underlayConn: &net.UDPConn{}, // non-nil to enable fast path
+		localIA:      srcIA,
+		localHostIP:  srcIP,
+		localPort:    srcPort,
+	}
+
+	pi := &scionPathInfo{
+		peerIA:   dstIA,
+		hostAddr: netip.MustParseAddrPort("127.0.0.1:32766"),
+		cachedDst: &snet.UDPAddr{
+			IA:      dstIA,
+			Host:    &net.UDPAddr{IP: net.IPv4(127, 0, 0, 1), Port: int(dstPort)},
+			Path:    snetpath.Empty{},
+			NextHop: &net.UDPAddr{IP: net.IPv4(127, 0, 0, 1), Port: 30041},
+		},
+	}
+
+	fp := buildSCIONFastPath(sc, pi)
+	if fp == nil {
+		t.Fatal("buildSCIONFastPath returned nil")
+	}
+
+	// The template should match a reference packet with empty payload.
+	refPkt := &snet.Packet{
+		PacketInfo: snet.PacketInfo{
+			Destination: snet.SCIONAddress{IA: dstIA, Host: addr.HostIP(dstIP)},
+			Source:      snet.SCIONAddress{IA: srcIA, Host: addr.HostIP(srcIP)},
+			Path:        snetpath.Empty{},
+			Payload: snet.UDPPayload{
+				SrcPort: srcPort,
+				DstPort: dstPort,
+				Payload: nil,
+			},
+		},
+	}
+	if err := refPkt.Serialize(); err != nil {
+		t.Fatalf("reference Serialize: %v", err)
+	}
+
+	if len(fp.hdr) != len(refPkt.Bytes) {
+		t.Fatalf("fast-path header len = %d, reference = %d", len(fp.hdr), len(refPkt.Bytes))
+	}
+
+	// Compare header bytes (everything except checksum which may differ
+	// due to computation order, but should be the same for empty payload).
+	for i := range fp.hdr {
+		if fp.hdr[i] != refPkt.Bytes[i] {
+			t.Errorf("byte %d: fast-path=0x%02x, reference=0x%02x", i, fp.hdr[i], refPkt.Bytes[i])
+		}
+	}
+
+	if fp.udpOffset != len(fp.hdr)-8 {
+		t.Errorf("udpOffset = %d, expected %d", fp.udpOffset, len(fp.hdr)-8)
+	}
+
+	if fp.nextHop == nil {
+		t.Error("nextHop should not be nil")
+	}
+}
+
+// TestSCIONFastPathPacketMatchesReference verifies that a packet built with
+// the fast-path template+patching produces identical bytes to one built with
+// snet.Packet.Serialize().
+func TestSCIONFastPathPacketMatchesReference(t *testing.T) {
+	srcIA := addr.MustParseIA("1-ff00:0:110")
+	dstIA := addr.MustParseIA("1-ff00:0:111")
+	srcIP := netip.MustParseAddr("127.0.0.1")
+	dstIP := netip.MustParseAddr("127.0.0.1")
+	srcPort := uint16(32766)
+	dstPort := uint16(32766)
+	payload := []byte("WireGuard test payload data for SCION fast path verification")
+
+	sc := &scionConn{
+		underlayConn: &net.UDPConn{},
+		localIA:      srcIA,
+		localHostIP:  srcIP,
+		localPort:    srcPort,
+	}
+
+	pi := &scionPathInfo{
+		peerIA:   dstIA,
+		hostAddr: netip.MustParseAddrPort("127.0.0.1:32766"),
+		cachedDst: &snet.UDPAddr{
+			IA:      dstIA,
+			Host:    &net.UDPAddr{IP: net.IPv4(127, 0, 0, 1), Port: int(dstPort)},
+			Path:    snetpath.Empty{},
+			NextHop: &net.UDPAddr{IP: net.IPv4(127, 0, 0, 1), Port: 30041},
+		},
+	}
+
+	fp := buildSCIONFastPath(sc, pi)
+	if fp == nil {
+		t.Fatal("buildSCIONFastPath returned nil")
+	}
+
+	// Build packet using fast-path template + patching.
+	hdrLen := len(fp.hdr)
+	pktLen := hdrLen + len(payload)
+	buf := make([]byte, pktLen)
+	copy(buf, fp.hdr)
+	copy(buf[hdrLen:], payload)
+
+	udpTotalLen := uint16(8 + len(payload))
+	binary.BigEndian.PutUint16(buf[6:], udpTotalLen)
+	binary.BigEndian.PutUint16(buf[fp.udpOffset+4:], udpTotalLen)
+	buf[fp.udpOffset+6] = 0
+	buf[fp.udpOffset+7] = 0
+	upperLayer := buf[fp.udpOffset:pktLen]
+	csum := scionFinishChecksum(fp.pseudoCsum, upperLayer)
+	binary.BigEndian.PutUint16(buf[fp.udpOffset+6:], csum)
+
+	// Build reference packet using snet.
+	refPkt := &snet.Packet{
+		PacketInfo: snet.PacketInfo{
+			Destination: snet.SCIONAddress{IA: dstIA, Host: addr.HostIP(dstIP)},
+			Source:      snet.SCIONAddress{IA: srcIA, Host: addr.HostIP(srcIP)},
+			Path:        snetpath.Empty{},
+			Payload: snet.UDPPayload{
+				SrcPort: srcPort,
+				DstPort: dstPort,
+				Payload: payload,
+			},
+		},
+	}
+	if err := refPkt.Serialize(); err != nil {
+		t.Fatalf("reference Serialize: %v", err)
+	}
+
+	if len(buf) != len(refPkt.Bytes) {
+		t.Fatalf("fast-path pkt len = %d, reference = %d", len(buf), len(refPkt.Bytes))
+	}
+
+	for i := range buf {
+		if buf[i] != refPkt.Bytes[i] {
+			t.Errorf("byte %d: fast-path=0x%02x, reference=0x%02x", i, buf[i], refPkt.Bytes[i])
+		}
+	}
+}
+
+// TestSCIONSendBatchPool verifies the pool returns usable batches.
+func TestSCIONSendBatchPool(t *testing.T) {
+	batch := scionSendBatchPool.Get().(*scionSendBatch)
+	defer scionSendBatchPool.Put(batch)
+
+	if len(batch.bufs) != scionMaxBatchSize {
+		t.Errorf("batch.bufs len = %d, want %d", len(batch.bufs), scionMaxBatchSize)
+	}
+	if len(batch.msgs) != scionMaxBatchSize {
+		t.Errorf("batch.msgs len = %d, want %d", len(batch.msgs), scionMaxBatchSize)
+	}
+	for i, buf := range batch.bufs {
+		if cap(buf) < 1500 {
+			t.Errorf("batch.bufs[%d] cap = %d, want >= 1500", i, cap(buf))
+		}
+	}
+	for i, msg := range batch.msgs {
+		if len(msg.Buffers) != 1 {
+			t.Errorf("batch.msgs[%d].Buffers len = %d, want 1", i, len(msg.Buffers))
+		}
+	}
+}
+
+// --- Tests for SCION Path Handling Improvements ---
+
+func TestScionInterfaceOverlap(t *testing.T) {
+	ctrl := gomock.NewController(t)
+
+	ifaceIA1 := addr.MustParseIA("1-ff00:0:110")
+	ifaceIA2 := addr.MustParseIA("1-ff00:0:111")
+	ifaceIA3 := addr.MustParseIA("1-ff00:0:112")
+
+	t.Run("full overlap", func(t *testing.T) {
+		a := newMockPathWithMetadata(ctrl, &snet.PathMetadata{
+			Interfaces: []snet.PathInterface{
+				{IA: ifaceIA1, ID: 1}, {IA: ifaceIA2, ID: 2},
+			},
+		})
+		b := newMockPathWithMetadata(ctrl, &snet.PathMetadata{
+			Interfaces: []snet.PathInterface{
+				{IA: ifaceIA1, ID: 1}, {IA: ifaceIA2, ID: 2},
+			},
+		})
+		got := interfaceOverlap(a, b)
+		if got != 1.0 {
+			t.Errorf("full overlap = %v, want 1.0", got)
+		}
+	})
+
+	t.Run("no overlap", func(t *testing.T) {
+		a := newMockPathWithMetadata(ctrl, &snet.PathMetadata{
+			Interfaces: []snet.PathInterface{
+				{IA: ifaceIA1, ID: 1},
+			},
+		})
+		b := newMockPathWithMetadata(ctrl, &snet.PathMetadata{
+			Interfaces: []snet.PathInterface{
+				{IA: ifaceIA2, ID: 2}, {IA: ifaceIA3, ID: 3},
+			},
+		})
+		got := interfaceOverlap(a, b)
+		if got != 0.0 {
+			t.Errorf("no overlap = %v, want 0.0", got)
+		}
+	})
+
+	t.Run("partial overlap", func(t *testing.T) {
+		a := newMockPathWithMetadata(ctrl, &snet.PathMetadata{
+			Interfaces: []snet.PathInterface{
+				{IA: ifaceIA1, ID: 1}, {IA: ifaceIA2, ID: 2},
+			},
+		})
+		b := newMockPathWithMetadata(ctrl, &snet.PathMetadata{
+			Interfaces: []snet.PathInterface{
+				{IA: ifaceIA1, ID: 1}, {IA: ifaceIA3, ID: 3},
+			},
+		})
+		got := interfaceOverlap(a, b)
+		if got != 0.5 {
+			t.Errorf("partial overlap = %v, want 0.5", got)
+		}
+	})
+
+	t.Run("nil metadata returns zero", func(t *testing.T) {
+		a := newMockPathWithMetadata(ctrl, nil)
+		b := newMockPathWithMetadata(ctrl, &snet.PathMetadata{
+			Interfaces: []snet.PathInterface{{IA: ifaceIA1, ID: 1}},
+		})
+		got := interfaceOverlap(a, b)
+		if got != 0.0 {
+			t.Errorf("nil metadata = %v, want 0.0", got)
+		}
+	})
+
+	t.Run("empty interfaces returns zero", func(t *testing.T) {
+		a := newMockPathWithMetadata(ctrl, &snet.PathMetadata{})
+		b := newMockPathWithMetadata(ctrl, &snet.PathMetadata{
+			Interfaces: []snet.PathInterface{{IA: ifaceIA1, ID: 1}},
+		})
+		got := interfaceOverlap(a, b)
+		if got != 0.0 {
+			t.Errorf("empty interfaces = %v, want 0.0", got)
+		}
+	})
+}
+
+func TestScionSelectDiversePaths(t *testing.T) {
+	ctrl := gomock.NewController(t)
+
+	ifaceIA1 := addr.MustParseIA("1-ff00:0:110")
+	ifaceIA2 := addr.MustParseIA("1-ff00:0:111")
+	ifaceIA3 := addr.MustParseIA("1-ff00:0:112")
+
+	t.Run("fewer candidates than max", func(t *testing.T) {
+		paths := []pathWithMeta{
+			{path: newMockPathWithMetadata(ctrl, &snet.PathMetadata{Latency: []time.Duration{10 * time.Millisecond}}), latency: 10 * time.Millisecond},
+			{path: newMockPathWithMetadata(ctrl, &snet.PathMetadata{Latency: []time.Duration{5 * time.Millisecond}}), latency: 5 * time.Millisecond},
+		}
+		result := selectDiversePaths(paths, 5)
+		if len(result) != 2 {
+			t.Fatalf("got %d paths, want 2", len(result))
+		}
+		// Should be sorted by latency.
+		if result[0].latency > result[1].latency {
+			t.Error("should be sorted by latency ascending")
+		}
+	})
+
+	t.Run("prefers diverse path over duplicate topology", func(t *testing.T) {
+		// Path A: fastest, through ifaceIA1+ifaceIA2.
+		pathA := newMockPathWithMetadata(ctrl, &snet.PathMetadata{
+			Latency:    []time.Duration{5 * time.Millisecond},
+			Interfaces: []snet.PathInterface{{IA: ifaceIA1, ID: 1}, {IA: ifaceIA2, ID: 2}},
+		})
+		// Path B: slightly slower, same interfaces as A.
+		pathB := newMockPathWithMetadata(ctrl, &snet.PathMetadata{
+			Latency:    []time.Duration{6 * time.Millisecond},
+			Interfaces: []snet.PathInterface{{IA: ifaceIA1, ID: 1}, {IA: ifaceIA2, ID: 2}},
+		})
+		// Path C: a bit slower, different interfaces.
+		pathC := newMockPathWithMetadata(ctrl, &snet.PathMetadata{
+			Latency:    []time.Duration{8 * time.Millisecond},
+			Interfaces: []snet.PathInterface{{IA: ifaceIA1, ID: 1}, {IA: ifaceIA3, ID: 3}},
+		})
+
+		candidates := []pathWithMeta{
+			{path: pathA, latency: 5 * time.Millisecond},
+			{path: pathB, latency: 6 * time.Millisecond},
+			{path: pathC, latency: 8 * time.Millisecond},
+		}
+		result := selectDiversePaths(candidates, 2)
+		if len(result) != 2 {
+			t.Fatalf("got %d paths, want 2", len(result))
+		}
+		// First should be pathA (lowest latency), second should be pathC (diverse).
+		if result[0].path != pathA {
+			t.Error("first path should be lowest-latency (pathA)")
+		}
+		if result[1].path != pathC {
+			t.Error("second path should be diverse (pathC), not duplicate (pathB)")
+		}
+	})
+}
+
+func TestScionStalePathCleanup(t *testing.T) {
+	ctrl := gomock.NewController(t)
+	mockDaemon := mock_daemon.NewMockConnector(ctrl)
+
+	localIA := addr.MustParseIA("1-ff00:0:110")
+	peerIA := addr.MustParseIA("1-ff00:0:111")
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	c := &Conn{
+		connCtx: ctx,
+		peerMap: newPeerMap(),
+	}
+	c.logf = t.Logf
+	c.pconnSCION.Store(&scionConn{daemon: mockDaemon, localIA: localIA})
+
+	// Register a path with a fingerprint that will disappear.
+	pi := &scionPathInfo{
+		peerIA:      peerIA,
+		hostAddr:    netip.MustParseAddrPort("10.0.0.1:41641"),
+		fingerprint: "stale-fp",
+		expiry:      time.Now().Add(30 * time.Second), // about to expire
+	}
+	k := c.registerSCIONPathLocking(pi)
+
+	// Daemon returns a path with a different fingerprint each time.
+	newPath := newMockPathWithMetadata(ctrl, &snet.PathMetadata{
+		Latency: []time.Duration{5 * time.Millisecond},
+		Expiry:  time.Now().Add(2 * time.Hour),
+	})
+
+	// Call refresh scionStalePathThreshold times.
+	for i := 0; i < scionStalePathThreshold; i++ {
+		mockDaemon.EXPECT().Paths(gomock.Any(), peerIA, localIA, daemon.PathReqFlags{Refresh: true}).
+			Return([]snet.Path{newPath}, nil)
+		c.refreshSCIONPathsOnce()
+	}
+
+	// Path should have been cleaned up.
+	got := c.lookupSCIONPathLocking(k)
+	if got != nil {
+		t.Error("stale path should have been removed after threshold exceeded")
+	}
+}
+
+func TestScionPathHealthTracking(t *testing.T) {
+	t.Run("pong resets consecutive loss and marks healthy", func(t *testing.T) {
+		ps := &scionPathProbeState{healthy: true}
+
+		// Simulate 2 losses.
+		ps.consecutiveLoss = 2
+		ps.pingsSent = 3
+
+		// Pong arrives.
+		ps.pongsReceived++
+		ps.consecutiveLoss = 0
+
+		if !ps.healthy {
+			t.Error("should still be healthy after pong")
+		}
+		if ps.consecutiveLoss != 0 {
+			t.Error("consecutive loss should be reset")
+		}
+		if ps.pongsReceived != 1 {
+			t.Errorf("pongsReceived = %d, want 1", ps.pongsReceived)
+		}
+	})
+
+	t.Run("three consecutive losses marks unhealthy", func(t *testing.T) {
+		ps := &scionPathProbeState{healthy: true}
+
+		for i := 0; i < 3; i++ {
+			ps.consecutiveLoss++
+		}
+
+		if ps.consecutiveLoss < 3 {
+			t.Error("should have 3 consecutive losses")
+		}
+		// In real code, demoteSCIONPathLocked would set healthy = false.
+		ps.healthy = false
+		if ps.healthy {
+			t.Error("should be unhealthy")
+		}
+	})
+
+	t.Run("recovery after unhealthy", func(t *testing.T) {
+		ps := &scionPathProbeState{healthy: false, consecutiveLoss: 5}
+
+		// Pong arrives — recovery.
+		ps.pongsReceived++
+		ps.consecutiveLoss = 0
+		ps.healthy = true
+
+		if !ps.healthy {
+			t.Error("should be healthy after recovery")
+		}
+	})
+}
+
+func TestScionDemoteSCIONPathLocked(t *testing.T) {
+	hostAddr := netip.MustParseAddrPort("10.0.0.1:41641")
+	peerIA := addr.MustParseIA("1-ff00:0:111")
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	c := &Conn{
+		connCtx: ctx,
+		peerMap: newPeerMap(),
+	}
+	c.logf = t.Logf
+
+	de := &endpoint{c: c}
+	de.scionState = &scionEndpointState{
+		peerIA:   peerIA,
+		hostAddr: hostAddr,
+		activePath: scionPathKey(1),
+		paths: map[scionPathKey]*scionPathProbeState{
+			scionPathKey(1): {healthy: false, recentPongs: [scionPongHistoryCount]scionPongReply{{latency: 50 * time.Millisecond}}, pongCount: 1, recentPong: 0},
+			scionPathKey(2): {healthy: true, recentPongs: [scionPongHistoryCount]scionPongReply{{latency: 30 * time.Millisecond}}, pongCount: 1, recentPong: 0},
+			scionPathKey(3): {healthy: true, recentPongs: [scionPongHistoryCount]scionPongReply{{latency: 40 * time.Millisecond}}, pongCount: 1, recentPong: 0},
+		},
+	}
+	de.bestAddr = addrQuality{
+		epAddr: epAddr{ap: hostAddr, scionKey: scionPathKey(1)},
+	}
+
+	de.mu.Lock()
+	de.demoteSCIONPathLocked(scionPathKey(1))
+	activePath := de.scionState.activePath
+	bestKey := de.bestAddr.scionKey
+	de.mu.Unlock()
+
+	if activePath != scionPathKey(2) {
+		t.Errorf("activePath = %d, want 2 (best healthy)", activePath)
+	}
+	if bestKey != scionPathKey(2) {
+		t.Errorf("bestAddr scionKey = %d, want 2", bestKey)
+	}
+}
+
+func TestScionReEvalSCIONPathsLocked(t *testing.T) {
+	hostAddr := netip.MustParseAddrPort("10.0.0.1:41641")
+	peerIA := addr.MustParseIA("1-ff00:0:111")
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	c := &Conn{
+		connCtx: ctx,
+		peerMap: newPeerMap(),
+	}
+	c.logf = t.Logf
+
+	de := &endpoint{c: c}
+	de.scionState = &scionEndpointState{
+		peerIA:   peerIA,
+		hostAddr: hostAddr,
+		activePath: scionPathKey(1),
+		paths: map[scionPathKey]*scionPathProbeState{
+			scionPathKey(1): {healthy: true, recentPongs: [scionPongHistoryCount]scionPongReply{{latency: 50 * time.Millisecond}}, pongCount: 1, recentPong: 0},
+			scionPathKey(2): {healthy: true, recentPongs: [scionPongHistoryCount]scionPongReply{{latency: 10 * time.Millisecond}}, pongCount: 1, recentPong: 0},
+		},
+	}
+	de.bestAddr = addrQuality{
+		epAddr: epAddr{ap: hostAddr, scionKey: scionPathKey(1)},
+		latency: 50 * time.Millisecond,
+	}
+
+	de.mu.Lock()
+	de.reEvalSCIONPathsLocked(mono.Now())
+	activePath := de.scionState.activePath
+	bestKey := de.bestAddr.scionKey
+	de.mu.Unlock()
+
+	// Path 2 has lower latency, should be selected.
+	if activePath != scionPathKey(2) {
+		t.Errorf("activePath = %d, want 2 (lower latency)", activePath)
+	}
+	if bestKey != scionPathKey(2) {
+		t.Errorf("bestAddr scionKey = %d, want 2", bestKey)
+	}
+}
+
+func TestScionProbeSCIONNonBestLocked(t *testing.T) {
+	// Test that probeSCIONNonBestLocked round-robins through non-active paths.
+	state := &scionEndpointState{
+		hostAddr:   netip.MustParseAddrPort("10.0.0.1:41641"),
+		activePath: scionPathKey(1),
+		paths: map[scionPathKey]*scionPathProbeState{
+			scionPathKey(1): {healthy: true},
+			scionPathKey(2): {healthy: true},
+			scionPathKey(3): {healthy: true},
+		},
+	}
+
+	// Collect non-active keys manually as probeSCIONNonBestLocked would.
+	var nonBest []scionPathKey
+	for k := range state.paths {
+		if k != state.activePath {
+			nonBest = append(nonBest, k)
+		}
+	}
+
+	if len(nonBest) != 2 {
+		t.Fatalf("expected 2 non-best paths, got %d", len(nonBest))
+	}
+
+	// Verify round-robin increments.
+	idx0 := state.probeRoundRobin % len(nonBest)
+	state.probeRoundRobin++
+	idx1 := state.probeRoundRobin % len(nonBest)
+	state.probeRoundRobin++
+
+	if idx0 == idx1 {
+		t.Error("round-robin should pick different paths on consecutive calls")
+	}
+}
+
+func TestDispatcherShim(t *testing.T) {
+	t.Run("binds_when_port_available", func(t *testing.T) {
+		sc := &scionConn{
+			localHostIP: netip.MustParseAddr("127.0.0.1"),
+			localPort:   32766,
+		}
+		openDispatcherShim(sc, t.Logf, nil)
+		if sc.shimConn == nil {
+			t.Fatal("expected shimConn to be set when port 30041 is available")
+		}
+		defer sc.shimConn.Close()
+		if sc.shimXPC == nil {
+			t.Fatal("expected shimXPC to be set")
+		}
+		addr := sc.shimConn.LocalAddr().(*net.UDPAddr)
+		if addr.Port != scionDispatcherPort {
+			t.Errorf("shimConn port = %d, want %d", addr.Port, scionDispatcherPort)
+		}
+	})
+
+	t.Run("graceful_on_EADDRINUSE", func(t *testing.T) {
+		// Occupy port 30041 first.
+		blocker, err := net.ListenUDP("udp", &net.UDPAddr{
+			IP:   net.IPv4(127, 0, 0, 1),
+			Port: scionDispatcherPort,
+		})
+		if err != nil {
+			t.Skipf("cannot bind port %d for test: %v", scionDispatcherPort, err)
+		}
+		defer blocker.Close()
+
+		sc := &scionConn{
+			localHostIP: netip.MustParseAddr("127.0.0.1"),
+			localPort:   32766,
+		}
+		openDispatcherShim(sc, t.Logf, nil)
+		if sc.shimConn != nil {
+			sc.shimConn.Close()
+			t.Fatal("expected shimConn to be nil when port is already in use")
+		}
+		if sc.shimXPC != nil {
+			t.Fatal("expected shimXPC to be nil when port is already in use")
+		}
+	})
+
+	t.Run("skipped_when_main_on_dispatcher_port", func(t *testing.T) {
+		sc := &scionConn{
+			localHostIP: netip.MustParseAddr("127.0.0.1"),
+			localPort:   scionDispatcherPort,
+		}
+		openDispatcherShim(sc, t.Logf, nil)
+		if sc.shimConn != nil {
+			sc.shimConn.Close()
+			t.Fatal("expected shimConn to be nil when main socket is on dispatcher port")
+		}
+	})
+}
+
+func TestFormatSCIONHops(t *testing.T) {
+	mustIA := func(s string) addr.IA {
+		ia, err := addr.ParseIA(s)
+		if err != nil {
+			t.Fatalf("invalid IA %q: %v", s, err)
+		}
+		return ia
+	}
+
+	tests := []struct {
+		name   string
+		ifaces []snet.PathInterface
+		want   string
+	}{
+		{
+			name:   "empty",
+			ifaces: nil,
+			want:   "?",
+		},
+		{
+			name: "single interface",
+			ifaces: []snet.PathInterface{
+				{IA: mustIA("19-ffaa:1:eba"), ID: 2},
+			},
+			want: "19-ffaa:1:eba 2",
+		},
+		{
+			name: "2-hop direct",
+			ifaces: []snet.PathInterface{
+				{IA: mustIA("19-ffaa:1:eba"), ID: 2},
+				{IA: mustIA("19-ffaa:1:bf5"), ID: 2},
+			},
+			want: "19-ffaa:1:eba 2>2 19-ffaa:1:bf5",
+		},
+		{
+			name: "3-hop via transit",
+			ifaces: []snet.PathInterface{
+				{IA: mustIA("19-ffaa:1:eba"), ID: 1},
+				{IA: mustIA("19-ffaa:0:1303"), ID: 62},
+				{IA: mustIA("19-ffaa:0:1303"), ID: 104},
+				{IA: mustIA("19-ffaa:1:bf5"), ID: 1},
+			},
+			want: "19-ffaa:1:eba 1>62 19-ffaa:0:1303 104>1 19-ffaa:1:bf5",
+		},
+		{
+			name: "4-hop two transits",
+			ifaces: []snet.PathInterface{
+				{IA: mustIA("19-ffaa:1:eba"), ID: 1},
+				{IA: mustIA("19-ffaa:0:1"), ID: 3},
+				{IA: mustIA("19-ffaa:0:1"), ID: 4},
+				{IA: mustIA("19-ffaa:0:2"), ID: 5},
+				{IA: mustIA("19-ffaa:0:2"), ID: 6},
+				{IA: mustIA("19-ffaa:1:bf5"), ID: 1},
+			},
+			want: "19-ffaa:1:eba 1>3 19-ffaa:0:1 4>5 19-ffaa:0:2 6>1 19-ffaa:1:bf5",
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := formatSCIONHops(tt.ifaces)
+			if got != tt.want {
+				t.Errorf("formatSCIONHops() = %q, want %q", got, tt.want)
+			}
+		})
+	}
+}
+
+func TestScionPathInfoString(t *testing.T) {
+	mustIA := func(s string) addr.IA {
+		ia, err := addr.ParseIA(s)
+		if err != nil {
+			t.Fatalf("invalid IA %q: %v", s, err)
+		}
+		return ia
+	}
+
+	pi := &scionPathInfo{
+		peerIA:   mustIA("19-ffaa:1:bf5"),
+		hostAddr: netip.MustParseAddrPort("127.0.0.1:32766"),
+		path: snetpath.Path{
+			Src: mustIA("19-ffaa:1:eba"),
+			Dst: mustIA("19-ffaa:1:bf5"),
+			Meta: snet.PathMetadata{
+				Interfaces: []snet.PathInterface{
+					{IA: mustIA("19-ffaa:1:eba"), ID: 2},
+					{IA: mustIA("19-ffaa:1:bf5"), ID: 2},
+				},
+				MTU: 1472,
+			},
+		},
+	}
+	pi.buildDisplayStr()
+
+	want := "scion:[19-ffaa:1:eba 2>2 19-ffaa:1:bf5]:[127.0.0.1]:32766"
+	if got := pi.String(); got != want {
+		t.Errorf("scionPathInfo.String() = %q, want %q", got, want)
+	}
+
+	// Test with no metadata
+	piNoMeta := &scionPathInfo{
+		peerIA:   mustIA("19-ffaa:1:bf5"),
+		hostAddr: netip.MustParseAddrPort("127.0.0.1:32766"),
+	}
+	piNoMeta.buildDisplayStr()
+
+	wantNoMeta := "scion:[?]:[127.0.0.1]:32766"
+	if got := piNoMeta.String(); got != wantNoMeta {
+		t.Errorf("scionPathInfo.String() no metadata = %q, want %q", got, wantNoMeta)
+	}
+}
+
+func TestScionLatencyMedian(t *testing.T) {
+	tests := []struct {
+		name    string
+		samples []time.Duration
+		want    time.Duration
+	}{
+		{
+			name:    "no samples",
+			samples: nil,
+			want:    time.Hour,
+		},
+		{
+			name:    "single sample",
+			samples: []time.Duration{10 * time.Millisecond},
+			want:    10 * time.Millisecond,
+		},
+		{
+			name:    "two samples returns higher (index 1)",
+			samples: []time.Duration{8 * time.Millisecond, 12 * time.Millisecond},
+			want:    12 * time.Millisecond,
+		},
+		{
+			name:    "four samples returns median",
+			samples: []time.Duration{10, 20, 30, 40},
+			want:    30, // samples[4/2] = samples[2]
+		},
+		{
+			name:    "eight samples median",
+			samples: []time.Duration{5, 10, 15, 20, 25, 30, 35, 40},
+			want:    25, // samples[8/2] = samples[4]
+		},
+		{
+			name:    "outlier resistance",
+			samples: []time.Duration{10, 11, 12, 10, 11, 12, 10, 500},
+			want:    11, // median ignores the 500 outlier
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			ps := &scionPathProbeState{}
+			for _, s := range tt.samples {
+				ps.addPongReply(scionPongReply{latency: s})
+			}
+			if got := ps.latency(); got != tt.want {
+				t.Errorf("latency() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+
+func TestScionReEvalAntiFlap(t *testing.T) {
+	hostAddr := netip.MustParseAddrPort("10.0.0.1:41641")
+	peerIA := addr.MustParseIA("1-ff00:0:111")
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	c := &Conn{
+		connCtx: ctx,
+		peerMap: newPeerMap(),
+	}
+	c.logf = t.Logf
+
+	// Two paths with very similar latency (10ms vs 11ms).
+	// Path 1 is the incumbent active path.
+	ps1 := &scionPathProbeState{healthy: true}
+	ps1.addPongReply(scionPongReply{latency: 10 * time.Millisecond})
+
+	ps2 := &scionPathProbeState{healthy: true}
+	ps2.addPongReply(scionPongReply{latency: 11 * time.Millisecond})
+
+	de := &endpoint{c: c}
+	de.scionState = &scionEndpointState{
+		peerIA:     peerIA,
+		hostAddr:   hostAddr,
+		activePath: scionPathKey(2), // path 2 is active at 11ms
+		paths: map[scionPathKey]*scionPathProbeState{
+			scionPathKey(1): ps1,
+			scionPathKey(2): ps2,
+		},
+	}
+	de.bestAddr = addrQuality{
+		epAddr:  epAddr{ap: hostAddr, scionKey: scionPathKey(2)},
+		latency: 11 * time.Millisecond,
+	}
+
+	// Re-eval should NOT switch — 1ms improvement is within 2ms minimum threshold.
+	de.mu.Lock()
+	de.reEvalSCIONPathsLocked(mono.Now())
+	activePath := de.scionState.activePath
+	de.mu.Unlock()
+
+	if activePath != scionPathKey(2) {
+		t.Errorf("anti-flap: activePath = %d, want 2 (should not switch for 1ms difference)", activePath)
+	}
+
+	// Now make path 1 significantly worse (50ms) and path 2 stays at 11ms.
+	// Then flip: make path 2 the slow one (50ms) and path 1 = 10ms.
+	// The 40ms improvement exceeds the 20% threshold (20% of 50ms = 10ms).
+	ps2Slow := &scionPathProbeState{healthy: true}
+	ps2Slow.addPongReply(scionPongReply{latency: 50 * time.Millisecond})
+
+	de.mu.Lock()
+	de.scionState.paths[scionPathKey(2)] = ps2Slow
+	de.scionState.lastFullEvalAt = 0 // reset throttle
+	de.bestAddr.latency = 50 * time.Millisecond
+	de.reEvalSCIONPathsLocked(mono.Now())
+	activePath = de.scionState.activePath
+	de.mu.Unlock()
+
+	if activePath != scionPathKey(1) {
+		t.Errorf("genuine degradation: activePath = %d, want 1 (should switch for 40ms improvement)", activePath)
+	}
+}
+
+// TestScionAddNewPathsRecovery verifies that addNewSCIONPathsForPeer
+// initializes scionState on an endpoint when the initial path discovery
+// failed (scionState == nil) but incoming SCION disco registered the
+// endpoint in the peerMap via handlePingLocked.
+func TestScionAddNewPathsRecovery(t *testing.T) {
+	ctrl := gomock.NewController(t)
+
+	localIA := addr.MustParseIA("1-ff00:0:110")
+	peerIA := addr.MustParseIA("1-ff00:0:111")
+	hostAddr := netip.MustParseAddrPort("10.0.0.1:41641")
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	c := &Conn{
+		connCtx: ctx,
+		peerMap: newPeerMap(),
+	}
+	c.logf = t.Logf
+	c.pconnSCION.Store(&scionConn{daemon: mock_daemon.NewMockConnector(ctrl), localIA: localIA})
+
+	// Create an endpoint and register it in the peerMap at the plain
+	// hostAddr — this is what handlePingLocked does for incoming SCION disco.
+	ep := &endpoint{c: c, nodeID: 1}
+	ep.publicKey = key.NewNode().Public()
+	ep.disco.Store(&endpointDisco{key: key.NewDisco().Public()})
+	c.peerMap.upsertEndpoint(ep, key.DiscoPublic{})
+	c.peerMap.setNodeKeyForEpAddr(epAddr{ap: hostAddr}, ep.publicKey)
+
+	// Simulate failed initial discovery: ep.scionState is nil.
+	if ep.scionState != nil {
+		t.Fatal("precondition: scionState should be nil")
+	}
+
+	// Register a reply-path in c.scionPaths (simulates handleSCIONDisco
+	// creating a path entry from an incoming disco ping).
+	replyPI := &scionPathInfo{
+		peerIA:      peerIA,
+		hostAddr:    hostAddr,
+		fingerprint: "reply-fp",
+		expiry:      time.Now().Add(1 * time.Hour),
+	}
+	replyPI.buildDisplayStr()
+	c.registerSCIONPathLocking(replyPI)
+
+	// Now soft refresh finds new paths from the daemon. Call
+	// addNewSCIONPathsForPeer with two mock paths.
+	p1 := newMockPathWithMetadata(ctrl, &snet.PathMetadata{
+		Latency: []time.Duration{5 * time.Millisecond},
+		Expiry:  time.Now().Add(2 * time.Hour),
+	})
+	p2 := newMockPathWithMetadata(ctrl, &snet.PathMetadata{
+		Latency: []time.Duration{10 * time.Millisecond},
+		Expiry:  time.Now().Add(2 * time.Hour),
+	})
+
+	newKeys := c.addNewSCIONPathsForPeer(peerIA, hostAddr, []snet.Path{p1, p2})
+	if len(newKeys) != 2 {
+		t.Fatalf("addNewSCIONPathsForPeer returned %d keys, want 2", len(newKeys))
+	}
+
+	// Verify recovery initialized scionState.
+	ep.mu.Lock()
+	defer ep.mu.Unlock()
+
+	if ep.scionState == nil {
+		t.Fatal("scionState should have been initialized by recovery")
+	}
+	if ep.scionState.peerIA != peerIA {
+		t.Errorf("peerIA = %s, want %s", ep.scionState.peerIA, peerIA)
+	}
+	if ep.scionState.hostAddr != hostAddr {
+		t.Errorf("hostAddr = %s, want %s", ep.scionState.hostAddr, hostAddr)
+	}
+	if len(ep.scionState.paths) != 2 {
+		t.Errorf("paths count = %d, want 2", len(ep.scionState.paths))
+	}
+	if !ep.scionState.activePath.IsSet() {
+		t.Error("activePath should be set")
+	}
+	// activePath should be one of the new keys.
+	if ep.scionState.activePath != newKeys[0] {
+		t.Errorf("activePath = %d, want %d (first new key)", ep.scionState.activePath, newKeys[0])
+	}
+	// Each probe state should be healthy.
+	for _, k := range newKeys {
+		ps, ok := ep.scionState.paths[k]
+		if !ok {
+			t.Errorf("missing probe state for key %d", k)
+			continue
+		}
+		if !ps.healthy {
+			t.Errorf("probe state for key %d should be healthy", k)
+		}
+	}
+}
diff --git a/wgengine/magicsock/magicsock_test.go b/wgengine/magicsock/magicsock_test.go
index 7a8a6374cd1bc..4ecea8b18a586 100644
--- a/wgengine/magicsock/magicsock_test.go
+++ b/wgengine/magicsock/magicsock_test.go
@@ -1191,15 +1191,19 @@ func testTwoDevicePing(t *testing.T, d *devices) {
 	m2.conn.SetConnectionCounter(m2.counts.Add)
 
 	checkStats := func(t *testing.T, m *magicStack, wantConns []netlogtype.Connection) {
+		t.Helper()
 		defer m.counts.Reset()
-		counts := m.counts.Clone()
-		for _, conn := range wantConns {
-			if _, ok := counts[conn]; ok {
-				return
+		if err := tstest.WaitFor(5*time.Second, func() error {
+			counts := m.counts.Clone()
+			for _, conn := range wantConns {
+				if _, ok := counts[conn]; ok {
+					return nil
+				}
 			}
+			return fmt.Errorf("missing any connection to %s from %s", wantConns, slicesx.MapKeys(counts))
+		}); err != nil {
+			t.Error(err)
 		}
-		t.Helper()
-		t.Errorf("missing any connection to %s from %s", wantConns, slicesx.MapKeys(counts))
 	}
 
 	addrPort := netip.MustParseAddrPort
@@ -1261,15 +1265,16 @@ func testTwoDevicePing(t *testing.T, d *devices) {
 	t.Run("compare-metrics-stats", func(t *testing.T) {
 		setT(t)
 		defer setT(outerT)
-		m1.conn.resetMetricsForTest()
 		m1.counts.Reset()
-		m2.conn.resetMetricsForTest()
 		m2.counts.Reset()
+		m1.conn.resetMetricsForTest()
+		m2.conn.resetMetricsForTest()
 		t.Logf("Metrics before: %s\n", m1.metrics.String())
 		ping1(t)
 		ping2(t)
 		assertConnStatsAndUserMetricsEqual(t, m1)
 		assertConnStatsAndUserMetricsEqual(t, m2)
+		assertGlobalMetricsMatchPerConn(t, m1, m2)
 		t.Logf("Metrics after: %s\n", m1.metrics.String())
 	})
 }
@@ -1290,6 +1295,7 @@ func (c *Conn) resetMetricsForTest() {
 }
 
 func assertConnStatsAndUserMetricsEqual(t *testing.T, ms *magicStack) {
+	t.Helper()
 	physIPv4RxBytes := int64(0)
 	physIPv4TxBytes := int64(0)
 	physDERPRxBytes := int64(0)
@@ -1312,7 +1318,6 @@ func assertConnStatsAndUserMetricsEqual(t *testing.T, ms *magicStack) {
 			physIPv4TxPackets += int64(count.TxPackets)
 		}
 	}
-	ms.counts.Reset()
 
 	metricIPv4RxBytes := ms.conn.metrics.inboundBytesIPv4Total.Value()
 	metricIPv4RxPackets := ms.conn.metrics.inboundPacketsIPv4Total.Value()
@@ -1324,30 +1329,64 @@ func assertConnStatsAndUserMetricsEqual(t *testing.T, ms *magicStack) {
 	metricDERPTxBytes := ms.conn.metrics.outboundBytesDERPTotal.Value()
 	metricDERPTxPackets := ms.conn.metrics.outboundPacketsDERPTotal.Value()
 
+	// Reset counts after reading all values to minimize the window where a
+	// background packet could increment metrics but miss the cloned counts.
+	ms.counts.Reset()
+
+	// Compare physical connection stats with per-conn user metrics.
+	// A rebind during the measurement window can reset the physical connection
+	// counter, causing physical stats to show 0 while user metrics recorded
+	// packets normally. Tolerate this by logging instead of failing.
+	checkPhysVsMetric := func(phys, metric int64, name string) {
+		if phys == metric {
+			return
+		}
+		if phys == 0 && metric > 0 {
+			t.Logf("%s: physical counter is 0 but metric is %d (possible rebind during measurement)", name, metric)
+			return
+		}
+		t.Errorf("%s: physical=%d, metric=%d", name, phys, metric)
+	}
+	checkPhysVsMetric(physDERPRxBytes, metricDERPRxBytes, "DERPRxBytes")
+	checkPhysVsMetric(physDERPTxBytes, metricDERPTxBytes, "DERPTxBytes")
+	checkPhysVsMetric(physIPv4RxBytes, metricIPv4RxBytes, "IPv4RxBytes")
+	checkPhysVsMetric(physIPv4TxBytes, metricIPv4TxBytes, "IPv4TxBytes")
+	checkPhysVsMetric(physDERPRxPackets, metricDERPRxPackets, "DERPRxPackets")
+	checkPhysVsMetric(physDERPTxPackets, metricDERPTxPackets, "DERPTxPackets")
+	checkPhysVsMetric(physIPv4RxPackets, metricIPv4RxPackets, "IPv4RxPackets")
+	checkPhysVsMetric(physIPv4TxPackets, metricIPv4TxPackets, "IPv4TxPackets")
+}
+
+// assertGlobalMetricsMatchPerConn validates that the global clientmetric
+// AggregateCounters match the sum of per-conn user metrics from both magicsock
+// instances. This tests the metric registration wiring rather than assuming
+// symmetric traffic between the two instances.
+func assertGlobalMetricsMatchPerConn(t *testing.T, m1, m2 *magicStack) {
+	t.Helper()
 	c := qt.New(t)
-	c.Assert(physDERPRxBytes, qt.Equals, metricDERPRxBytes)
-	c.Assert(physDERPTxBytes, qt.Equals, metricDERPTxBytes)
-	c.Assert(physIPv4RxBytes, qt.Equals, metricIPv4RxBytes)
-	c.Assert(physIPv4TxBytes, qt.Equals, metricIPv4TxBytes)
-	c.Assert(physDERPRxPackets, qt.Equals, metricDERPRxPackets)
-	c.Assert(physDERPTxPackets, qt.Equals, metricDERPTxPackets)
-	c.Assert(physIPv4RxPackets, qt.Equals, metricIPv4RxPackets)
-	c.Assert(physIPv4TxPackets, qt.Equals, metricIPv4TxPackets)
-
-	// Validate that the usermetrics and clientmetrics are in sync
-	// Note: the clientmetrics are global, this means that when they are registering with the
-	// wgengine, multiple in-process nodes used by this test will be updating the same metrics. This is why we need to multiply
-	// the metrics by 2 to get the expected value.
-	// TODO(kradalby): https://github.com/tailscale/tailscale/issues/13420
-	c.Assert(metricSendUDP.Value(), qt.Equals, metricIPv4TxPackets*2)
-	c.Assert(metricSendDataPacketsIPv4.Value(), qt.Equals, metricIPv4TxPackets*2)
-	c.Assert(metricSendDataPacketsDERP.Value(), qt.Equals, metricDERPTxPackets*2)
-	c.Assert(metricSendDataBytesIPv4.Value(), qt.Equals, metricIPv4TxBytes*2)
-	c.Assert(metricSendDataBytesDERP.Value(), qt.Equals, metricDERPTxBytes*2)
-	c.Assert(metricRecvDataPacketsIPv4.Value(), qt.Equals, metricIPv4RxPackets*2)
-	c.Assert(metricRecvDataPacketsDERP.Value(), qt.Equals, metricDERPRxPackets*2)
-	c.Assert(metricRecvDataBytesIPv4.Value(), qt.Equals, metricIPv4RxBytes*2)
-	c.Assert(metricRecvDataBytesDERP.Value(), qt.Equals, metricDERPRxBytes*2)
+	m1m := m1.conn.metrics
+	m2m := m2.conn.metrics
+
+	// metricSendUDP aggregates outboundPacketsIPv4Total + outboundPacketsIPv6Total
+	c.Assert(metricSendUDP.Value(), qt.Equals,
+		m1m.outboundPacketsIPv4Total.Value()+m1m.outboundPacketsIPv6Total.Value()+
+			m2m.outboundPacketsIPv4Total.Value()+m2m.outboundPacketsIPv6Total.Value())
+	c.Assert(metricSendDataPacketsIPv4.Value(), qt.Equals,
+		m1m.outboundPacketsIPv4Total.Value()+m2m.outboundPacketsIPv4Total.Value())
+	c.Assert(metricSendDataPacketsDERP.Value(), qt.Equals,
+		m1m.outboundPacketsDERPTotal.Value()+m2m.outboundPacketsDERPTotal.Value())
+	c.Assert(metricSendDataBytesIPv4.Value(), qt.Equals,
+		m1m.outboundBytesIPv4Total.Value()+m2m.outboundBytesIPv4Total.Value())
+	c.Assert(metricSendDataBytesDERP.Value(), qt.Equals,
+		m1m.outboundBytesDERPTotal.Value()+m2m.outboundBytesDERPTotal.Value())
+	c.Assert(metricRecvDataPacketsIPv4.Value(), qt.Equals,
+		m1m.inboundPacketsIPv4Total.Value()+m2m.inboundPacketsIPv4Total.Value())
+	c.Assert(metricRecvDataPacketsDERP.Value(), qt.Equals,
+		m1m.inboundPacketsDERPTotal.Value()+m2m.inboundPacketsDERPTotal.Value())
+	c.Assert(metricRecvDataBytesIPv4.Value(), qt.Equals,
+		m1m.inboundBytesIPv4Total.Value()+m2m.inboundBytesIPv4Total.Value())
+	c.Assert(metricRecvDataBytesDERP.Value(), qt.Equals,
+		m1m.inboundBytesDERPTotal.Value()+m2m.inboundBytesDERPTotal.Value())
 }
 
 // tests that having a endpoint.String prevents wireguard-go's
diff --git a/wgengine/magicsock/scion_bootstrap.go b/wgengine/magicsock/scion_bootstrap.go
new file mode 100644
index 0000000000000..a2fef787844b6
--- /dev/null
+++ b/wgengine/magicsock/scion_bootstrap.go
@@ -0,0 +1,249 @@
+// Copyright (c) Tailscale Inc & contributors
+// SPDX-License-Identifier: BSD-3-Clause
+
+//go:build !ts_omit_scion
+
+package magicsock
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"io"
+	"net"
+	"net/http"
+	"os"
+	"path/filepath"
+	"strings"
+	"time"
+
+	"tailscale.com/atomicfile"
+	"tailscale.com/envknob"
+	"tailscale.com/types/logger"
+)
+
+const (
+	// bootstrapHTTPTimeout is the timeout for HTTP requests to the bootstrap server.
+	bootstrapHTTPTimeout = 10 * time.Second
+
+	// scionDiscoverySRV is the SRV record name for SCION discovery.
+	scionDiscoverySRV = "_sciondiscovery._tcp"
+)
+
+// defaultBootstrapURLs contains well-known bootstrap server URLs for major
+// SCION deployments. Populated as deployments are identified; DNS discovery
+// is the primary automatic mechanism.
+var defaultBootstrapURLs []string = []string{
+	"http://141.44.25.151:8041", // ovgu.de
+	"http://128.143.201.144:8041", // uva
+	"http://netsec-w37w3w.inf.ethz.ch:8041", // ethz.ch
+}
+
+var (
+	scionBootstrapURL  = envknob.RegisterString("TS_SCION_BOOTSTRAP_URL")
+	scionBootstrapURLs = envknob.RegisterString("TS_SCION_BOOTSTRAP_URLS")
+)
+
+// bootstrapSCION fetches topology.json and TRCs from a bootstrap server,
+// saving them to destDir.
+func bootstrapSCION(ctx context.Context, logf logger.Logf, serverURL string, destDir string) error {
+	if err := os.MkdirAll(destDir, 0o700); err != nil {
+		return fmt.Errorf("creating bootstrap directory %s: %w", destDir, err)
+	}
+
+	client := &http.Client{Timeout: bootstrapHTTPTimeout}
+
+	// Fetch topology.
+	topoURL := strings.TrimRight(serverURL, "/") + "/topology"
+	topoData, err := httpGet(ctx, client, topoURL)
+	if err != nil {
+		return fmt.Errorf("fetching topology from %s: %w", topoURL, err)
+	}
+	topoPath := filepath.Join(destDir, "topology.json")
+	if err := atomicfile.WriteFile(topoPath, topoData, 0o644); err != nil {
+		return fmt.Errorf("writing topology to %s: %w", topoPath, err)
+	}
+	logf("scion: bootstrap: fetched topology from %s", serverURL)
+
+	// Fetch TRC index.
+	trcsURL := strings.TrimRight(serverURL, "/") + "/trcs"
+	trcsData, err := httpGet(ctx, client, trcsURL)
+	if err != nil {
+		// TRCs are optional for Phase 1 (accept-all verification).
+		logf("scion: bootstrap: TRC index not available from %s: %v", serverURL, err)
+		return nil
+	}
+
+	certsDir := filepath.Join(destDir, "certs")
+	if err := os.MkdirAll(certsDir, 0o700); err != nil {
+		return fmt.Errorf("creating certs directory %s: %w", certsDir, err)
+	}
+
+	// Parse TRC index and fetch each TRC blob.
+	var trcIndex []trcEntry
+	if err := json.Unmarshal(trcsData, &trcIndex); err != nil {
+		// Non-fatal: TRC index may not be JSON array on all servers.
+		logf("scion: bootstrap: failed to parse TRC index: %v", err)
+		return nil
+	}
+
+	fetched := 0
+	for _, entry := range trcIndex {
+		if entry.ID.ISD == 0 {
+			continue // skip unparseable entries
+		}
+		idStr := entry.ID.String()
+		blobURL := strings.TrimRight(serverURL, "/") + "/trcs/" + idStr + "/blob"
+		blob, err := httpGet(ctx, client, blobURL)
+		if err != nil {
+			continue // Best-effort TRC download.
+		}
+		trcPath := filepath.Join(certsDir, idStr+".trc")
+		if err := atomicfile.WriteFile(trcPath, blob, 0o644); err != nil {
+			continue
+		}
+		fetched++
+	}
+	logf("scion: bootstrap: fetched %d/%d TRCs from %s", fetched, len(trcIndex), serverURL)
+
+	return nil
+}
+
+// trcEntry represents an entry in the TRC index returned by the bootstrap server.
+// The server returns {"id": {"isd": 19, "base_number": 1, "serial_number": 1}}.
+type trcEntry struct {
+	ID trcID `json:"id"`
+}
+
+// trcID represents the composite identifier for a TRC.
+type trcID struct {
+	ISD          int `json:"isd"`
+	BaseNumber   int `json:"base_number"`
+	SerialNumber int `json:"serial_number"`
+}
+
+// String returns a filesystem-safe representation of the TRC ID,
+// e.g. "isd19-b1-s1".
+func (id trcID) String() string {
+	return fmt.Sprintf("isd%d-b%d-s%d", id.ISD, id.BaseNumber, id.SerialNumber)
+}
+
+// discoverBootstrapURL attempts DNS-based discovery of a SCION bootstrap server.
+// It follows the JPAN discovery chain:
+//  1. SRV lookup for _sciondiscovery._tcp.<domain>
+//  2. TXT lookup for _sciondiscovery._tcp.<domain> for port override
+func discoverBootstrapURL(ctx context.Context, logf logger.Logf) (string, error) {
+	// Determine local search domain from system resolver.
+	domain, err := localSearchDomain()
+	if err != nil {
+		return "", fmt.Errorf("determining search domain: %w", err)
+	}
+	if domain == "" {
+		return "", fmt.Errorf("no search domain found")
+	}
+
+	r := &net.Resolver{}
+
+	// Try SRV lookup.
+	_, addrs, err := r.LookupSRV(ctx, "sciondiscovery", "tcp", domain)
+	if err != nil || len(addrs) == 0 {
+		return "", fmt.Errorf("SRV lookup for %s.%s failed: %w", scionDiscoverySRV, domain, err)
+	}
+
+	host := strings.TrimRight(addrs[0].Target, ".")
+	port := fmt.Sprintf("%d", addrs[0].Port)
+
+	// Check for TXT record port override.
+	if txtPort, err := lookupDiscoveryPort(ctx, r, domain); err == nil && txtPort != "" {
+		port = txtPort
+	}
+
+	url := fmt.Sprintf("http://%s:%s", host, port)
+	logf("scion: bootstrap: discovered %s via DNS SRV for %s", url, domain)
+	return url, nil
+}
+
+// lookupDiscoveryPort queries TXT records for the discovery port override.
+func lookupDiscoveryPort(ctx context.Context, r *net.Resolver, domain string) (string, error) {
+	name := scionDiscoverySRV + "." + domain
+	txts, err := r.LookupTXT(ctx, name)
+	if err != nil {
+		return "", err
+	}
+	for _, txt := range txts {
+		if strings.HasPrefix(txt, "x-sciondiscovery=") {
+			return strings.TrimPrefix(txt, "x-sciondiscovery="), nil
+		}
+	}
+	return "", fmt.Errorf("no x-sciondiscovery TXT record found")
+}
+
+// localSearchDomainFromHostname infers the search domain from the
+// system hostname. Used as a fallback on platforms where the primary
+// DNS discovery method fails.
+func localSearchDomainFromHostname() (string, error) {
+	hostname, err := os.Hostname()
+	if err != nil {
+		return "", err
+	}
+	if i := strings.IndexByte(hostname, '.'); i >= 0 {
+		return hostname[i+1:], nil
+	}
+	return "", fmt.Errorf("no domain suffix in hostname %q", hostname)
+}
+
+// httpGet performs an HTTP GET request and returns the response body.
+func httpGet(ctx context.Context, client *http.Client, url string) ([]byte, error) {
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
+	if err != nil {
+		return nil, err
+	}
+	resp, err := client.Do(req)
+	if err != nil {
+		return nil, err
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		return nil, fmt.Errorf("HTTP %d from %s", resp.StatusCode, url)
+	}
+
+	// Limit response body to 10MB to prevent excessive memory usage.
+	body, err := io.ReadAll(io.LimitReader(resp.Body, 10<<20))
+	if err != nil {
+		return nil, err
+	}
+	return body, nil
+}
+
+// bootstrapURLs returns the list of bootstrap URLs to try, from explicit
+// configuration, DNS discovery, and hardcoded defaults.
+func bootstrapURLs(ctx context.Context, logf logger.Logf) []string {
+	var urls []string
+
+	// Explicit URL from environment.
+	if u := scionBootstrapURL(); u != "" {
+		urls = append(urls, u)
+	}
+
+	// Comma-separated list from environment.
+	if u := scionBootstrapURLs(); u != "" {
+		for _, url := range strings.Split(u, ",") {
+			url = strings.TrimSpace(url)
+			if url != "" {
+				urls = append(urls, url)
+			}
+		}
+	}
+
+	// DNS-discovered URL.
+	if discovered, err := discoverBootstrapURL(ctx, logf); err == nil {
+		urls = append(urls, discovered)
+	}
+
+	// Hardcoded defaults.
+	urls = append(urls, defaultBootstrapURLs...)
+
+	logf("scion: bootstrap: %d URLs to try", len(urls))
+	return urls
+}
diff --git a/wgengine/magicsock/scion_bootstrap_other.go b/wgengine/magicsock/scion_bootstrap_other.go
new file mode 100644
index 0000000000000..13540c1ece40d
--- /dev/null
+++ b/wgengine/magicsock/scion_bootstrap_other.go
@@ -0,0 +1,12 @@
+// Copyright (c) Tailscale Inc & contributors
+// SPDX-License-Identifier: BSD-3-Clause
+
+//go:build !ts_omit_scion && !(linux || darwin || freebsd || openbsd || netbsd || windows)
+
+package magicsock
+
+// localSearchDomain returns the search domain on platforms without
+// resolv.conf or winipcfg (e.g. Android). Falls back to hostname parsing.
+func localSearchDomain() (string, error) {
+	return localSearchDomainFromHostname()
+}
diff --git a/wgengine/magicsock/scion_bootstrap_test.go b/wgengine/magicsock/scion_bootstrap_test.go
new file mode 100644
index 0000000000000..25e1cea4b2949
--- /dev/null
+++ b/wgengine/magicsock/scion_bootstrap_test.go
@@ -0,0 +1,180 @@
+// Copyright (c) Tailscale Inc & contributors
+// SPDX-License-Identifier: BSD-3-Clause
+
+//go:build !ts_omit_scion
+
+package magicsock
+
+import (
+	"context"
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"tailscale.com/envknob"
+	"tailscale.com/types/logger"
+)
+
+func TestTrcIDString(t *testing.T) {
+	tests := []struct {
+		id   trcID
+		want string
+	}{
+		{trcID{ISD: 19, BaseNumber: 1, SerialNumber: 1}, "isd19-b1-s1"},
+		{trcID{ISD: 1, BaseNumber: 2, SerialNumber: 3}, "isd1-b2-s3"},
+		{trcID{ISD: 0, BaseNumber: 0, SerialNumber: 0}, "isd0-b0-s0"},
+	}
+	for _, tt := range tests {
+		got := tt.id.String()
+		if got != tt.want {
+			t.Errorf("trcID%+v.String() = %q, want %q", tt.id, got, tt.want)
+		}
+	}
+}
+
+func TestTrcIndexParsing(t *testing.T) {
+	// Real bootstrap server JSON format.
+	raw := `[{"id":{"isd":19,"base_number":1,"serial_number":1}},{"id":{"isd":19,"base_number":1,"serial_number":2}}]`
+	var entries []trcEntry
+	if err := json.Unmarshal([]byte(raw), &entries); err != nil {
+		t.Fatalf("Unmarshal: %v", err)
+	}
+	if len(entries) != 2 {
+		t.Fatalf("got %d entries, want 2", len(entries))
+	}
+	if got := entries[0].ID.ISD; got != 19 {
+		t.Errorf("entries[0].ID.ISD = %d, want 19", got)
+	}
+	if got := entries[0].ID.String(); got != "isd19-b1-s1" {
+		t.Errorf("entries[0].ID.String() = %q, want %q", got, "isd19-b1-s1")
+	}
+	if got := entries[1].ID.String(); got != "isd19-b1-s2" {
+		t.Errorf("entries[1].ID.String() = %q, want %q", got, "isd19-b1-s2")
+	}
+}
+
+func TestTrcIndexParsingOldFormat(t *testing.T) {
+	// The old flat string format ({"id": "ISD19-B1-S1"}) is incompatible
+	// with the nested struct. json.Unmarshal should return an error,
+	// and bootstrapSCION handles this gracefully (non-fatal).
+	raw := `[{"id":"ISD19-B1-S1"}]`
+	var entries []trcEntry
+	if err := json.Unmarshal([]byte(raw), &entries); err == nil {
+		t.Fatal("expected Unmarshal error for old string format, got nil")
+	}
+}
+
+func TestBootstrapSCION(t *testing.T) {
+	topoJSON := `{"isd_as":"19-ffaa:1:eba","mtu":1472}`
+	trcBlob := []byte("fake-trc-blob")
+	trcIndex := `[{"id":{"isd":19,"base_number":1,"serial_number":1}}]`
+
+	mux := http.NewServeMux()
+	mux.HandleFunc("/topology", func(w http.ResponseWriter, r *http.Request) {
+		w.Write([]byte(topoJSON))
+	})
+	mux.HandleFunc("/trcs", func(w http.ResponseWriter, r *http.Request) {
+		w.Write([]byte(trcIndex))
+	})
+	mux.HandleFunc("/trcs/isd19-b1-s1/blob", func(w http.ResponseWriter, r *http.Request) {
+		w.Write(trcBlob)
+	})
+	srv := httptest.NewServer(mux)
+	defer srv.Close()
+
+	destDir := t.TempDir()
+	logf := logger.WithPrefix(t.Logf, "test: ")
+
+	if err := bootstrapSCION(context.Background(), logf, srv.URL, destDir); err != nil {
+		t.Fatalf("bootstrapSCION: %v", err)
+	}
+
+	// Verify topology file.
+	topoPath := filepath.Join(destDir, "topology.json")
+	data, err := os.ReadFile(topoPath)
+	if err != nil {
+		t.Fatalf("reading topology: %v", err)
+	}
+	if string(data) != topoJSON {
+		t.Errorf("topology content = %q, want %q", data, topoJSON)
+	}
+
+	// Verify TRC file.
+	trcPath := filepath.Join(destDir, "certs", "isd19-b1-s1.trc")
+	data, err = os.ReadFile(trcPath)
+	if err != nil {
+		t.Fatalf("reading TRC: %v", err)
+	}
+	if string(data) != string(trcBlob) {
+		t.Errorf("TRC content = %q, want %q", data, trcBlob)
+	}
+}
+
+func TestBootstrapSCIONTopologyOnly(t *testing.T) {
+	// Server that returns topology but 404 on TRCs — should succeed.
+	topoJSON := `{"isd_as":"19-ffaa:1:eba"}`
+
+	mux := http.NewServeMux()
+	mux.HandleFunc("/topology", func(w http.ResponseWriter, r *http.Request) {
+		w.Write([]byte(topoJSON))
+	})
+	srv := httptest.NewServer(mux)
+	defer srv.Close()
+
+	destDir := t.TempDir()
+	logf := logger.WithPrefix(t.Logf, "test: ")
+
+	if err := bootstrapSCION(context.Background(), logf, srv.URL, destDir); err != nil {
+		t.Fatalf("bootstrapSCION: %v", err)
+	}
+
+	data, err := os.ReadFile(filepath.Join(destDir, "topology.json"))
+	if err != nil {
+		t.Fatalf("reading topology: %v", err)
+	}
+	if string(data) != topoJSON {
+		t.Errorf("topology content = %q, want %q", data, topoJSON)
+	}
+}
+
+func TestBootstrapURLs(t *testing.T) {
+	logf := logger.WithPrefix(t.Logf, "test: ")
+
+	// Use envknob.Setenv so the registered knob functions see the values.
+	envknob.Setenv("TS_SCION_BOOTSTRAP_URL", "http://explicit:8041")
+	t.Cleanup(func() { envknob.Setenv("TS_SCION_BOOTSTRAP_URL", "") })
+	envknob.Setenv("TS_SCION_BOOTSTRAP_URLS", "http://list1:8041, http://list2:8041")
+	t.Cleanup(func() { envknob.Setenv("TS_SCION_BOOTSTRAP_URLS", "") })
+
+	urls := bootstrapURLs(context.Background(), logf)
+
+	if len(urls) < 4 {
+		t.Fatalf("expected at least 4 URLs, got %d: %v", len(urls), urls)
+	}
+	if urls[0] != "http://explicit:8041" {
+		t.Errorf("urls[0] = %q, want explicit URL", urls[0])
+	}
+	if urls[1] != "http://list1:8041" {
+		t.Errorf("urls[1] = %q, want list1", urls[1])
+	}
+	if urls[2] != "http://list2:8041" {
+		t.Errorf("urls[2] = %q, want list2", urls[2])
+	}
+
+	// Hardcoded defaults should be at the end.
+	tail := urls[len(urls)-len(defaultBootstrapURLs):]
+	for i, want := range defaultBootstrapURLs {
+		if tail[i] != want {
+			t.Errorf("tail[%d] = %q, want %q", i, tail[i], want)
+		}
+	}
+}
+
+func TestLocalSearchDomainFromHostname(t *testing.T) {
+	// We can't easily override os.Hostname() in tests, so just verify
+	// the function doesn't panic and returns without error on this host.
+	_, _ = localSearchDomainFromHostname()
+}
diff --git a/wgengine/magicsock/scion_bootstrap_unix.go b/wgengine/magicsock/scion_bootstrap_unix.go
new file mode 100644
index 0000000000000..795ee1631e062
--- /dev/null
+++ b/wgengine/magicsock/scion_bootstrap_unix.go
@@ -0,0 +1,23 @@
+// Copyright (c) Tailscale Inc & contributors
+// SPDX-License-Identifier: BSD-3-Clause
+
+//go:build !ts_omit_scion && (linux || darwin || freebsd || openbsd || netbsd)
+
+package magicsock
+
+import (
+	"tailscale.com/net/dns/resolvconffile"
+)
+
+// localSearchDomain returns the first search domain from the system's DNS
+// configuration, using Tailscale's resolv.conf parser.
+func localSearchDomain() (string, error) {
+	cfg, err := resolvconffile.ParseFile(resolvconffile.Path)
+	if err != nil {
+		return localSearchDomainFromHostname()
+	}
+	if len(cfg.SearchDomains) > 0 {
+		return cfg.SearchDomains[0].WithoutTrailingDot(), nil
+	}
+	return localSearchDomainFromHostname()
+}
diff --git a/wgengine/magicsock/scion_bootstrap_windows.go b/wgengine/magicsock/scion_bootstrap_windows.go
new file mode 100644
index 0000000000000..1986468265597
--- /dev/null
+++ b/wgengine/magicsock/scion_bootstrap_windows.go
@@ -0,0 +1,63 @@
+// Copyright (c) Tailscale Inc & contributors
+// SPDX-License-Identifier: BSD-3-Clause
+
+//go:build !ts_omit_scion && windows
+
+package magicsock
+
+import (
+	"golang.org/x/sys/windows"
+	"golang.zx2c4.com/wireguard/windows/tunnel/winipcfg"
+)
+
+// localSearchDomain returns the DNS suffix from the default network adapter
+// on Windows, using winipcfg.GetAdaptersAddresses. Falls back to hostname
+// parsing if no adapter suffix is found.
+func localSearchDomain() (string, error) {
+	iface, err := getWindowsDefaultAdapter()
+	if err == nil && iface != nil {
+		if suffix := iface.DNSSuffix(); suffix != "" {
+			return suffix, nil
+		}
+	}
+	return localSearchDomainFromHostname()
+}
+
+// getWindowsDefaultAdapter returns the default IPv4 network adapter.
+func getWindowsDefaultAdapter() (*winipcfg.IPAdapterAddresses, error) {
+	ifs, err := winipcfg.GetAdaptersAddresses(windows.AF_INET, winipcfg.GAAFlagIncludeAllInterfaces)
+	if err != nil {
+		return nil, err
+	}
+
+	routes, err := winipcfg.GetIPForwardTable2(windows.AF_INET)
+	if err != nil {
+		return nil, err
+	}
+
+	// Index adapters by LUID, filtering to operational non-loopback interfaces.
+	byLUID := make(map[winipcfg.LUID]*winipcfg.IPAdapterAddresses)
+	for _, iface := range ifs {
+		if iface.OperStatus == winipcfg.IfOperStatusUp && iface.IfType != winipcfg.IfTypeSoftwareLoopback {
+			byLUID[iface.LUID] = iface
+		}
+	}
+
+	// Find the default route (prefix length 0) with the lowest metric.
+	bestMetric := ^uint32(0)
+	var best *winipcfg.IPAdapterAddresses
+	for _, route := range routes {
+		if route.DestinationPrefix.PrefixLength != 0 {
+			continue
+		}
+		iface := byLUID[route.InterfaceLUID]
+		if iface == nil {
+			continue
+		}
+		if route.Metric < bestMetric {
+			bestMetric = route.Metric
+			best = iface
+		}
+	}
+	return best, nil
+}
diff --git a/wgengine/magicsock/scion_embedded.go b/wgengine/magicsock/scion_embedded.go
new file mode 100644
index 0000000000000..e8863130a762a
--- /dev/null
+++ b/wgengine/magicsock/scion_embedded.go
@@ -0,0 +1,356 @@
+// Copyright (c) Tailscale Inc & contributors
+// SPDX-License-Identifier: BSD-3-Clause
+
+//go:build !ts_omit_scion
+
+package magicsock
+
+import (
+	"context"
+	"fmt"
+	"net"
+	"net/netip"
+	"os"
+	"path/filepath"
+	"runtime"
+
+	"github.com/scionproto/scion/daemon/config"
+	"github.com/scionproto/scion/daemon/fetcher"
+	"github.com/scionproto/scion/pkg/addr"
+	"github.com/scionproto/scion/pkg/daemon"
+	"github.com/scionproto/scion/pkg/drkey"
+	libgrpc "github.com/scionproto/scion/pkg/grpc"
+	"github.com/scionproto/scion/pkg/private/ctrl/path_mgmt"
+	"github.com/scionproto/scion/pkg/private/serrors"
+	cryptopb "github.com/scionproto/scion/pkg/proto/crypto"
+	"github.com/scionproto/scion/pkg/scrypto/cppki"
+	"github.com/scionproto/scion/pkg/scrypto/signed"
+	"github.com/scionproto/scion/pkg/segment/iface"
+	"github.com/scionproto/scion/pkg/snet"
+	segfetchergrpc "github.com/scionproto/scion/private/segment/segfetcher/grpc"
+	infra "github.com/scionproto/scion/private/segment/verifier"
+	"github.com/scionproto/scion/private/revcache"
+	"github.com/scionproto/scion/private/storage"
+	"github.com/scionproto/scion/private/topology"
+	"github.com/scionproto/scion/private/trust"
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/credentials/insecure"
+	"google.golang.org/grpc/resolver"
+	"google.golang.org/grpc/resolver/manual"
+	"tailscale.com/envknob"
+	"tailscale.com/net/netmon"
+	"tailscale.com/net/netns"
+	"tailscale.com/paths"
+	"tailscale.com/types/logger"
+)
+
+var (
+	scionTopology = envknob.RegisterString("TS_SCION_TOPOLOGY")
+	scionStateDirEnv = envknob.RegisterString("TS_SCION_STATE_DIR")
+)
+
+// embeddedConnector implements daemon.Connector using an embedded topology
+// loader and path fetcher, eliminating the need for an external SCION daemon
+// process.
+type embeddedConnector struct {
+	topo     *topology.Loader
+	fetcher  fetcher.Fetcher
+	pathDB   storage.PathDB
+	revCache revcache.RevCache
+	cancel   context.CancelFunc // cancels the topology loader goroutine
+}
+
+// Compile-time interface check.
+var _ daemon.Connector = (*embeddedConnector)(nil)
+
+// LocalIA returns the local ISD-AS from the topology.
+func (ec *embeddedConnector) LocalIA(_ context.Context) (addr.IA, error) {
+	return ec.topo.IA(), nil
+}
+
+// PortRange returns the endhost port range from the topology.
+func (ec *embeddedConnector) PortRange(_ context.Context) (uint16, uint16, error) {
+	min, max := ec.topo.PortRange()
+	return min, max, nil
+}
+
+// Interfaces returns the interface-to-underlay address map from the topology.
+func (ec *embeddedConnector) Interfaces(_ context.Context) (map[uint16]netip.AddrPort, error) {
+	ifInfoMap := ec.topo.InterfaceInfoMap()
+	result := make(map[uint16]netip.AddrPort, len(ifInfoMap))
+	for id, info := range ifInfoMap {
+		result[uint16(id)] = info.InternalAddr
+	}
+	return result, nil
+}
+
+// snetTopology returns an snet.Topology struct built from the embedded
+// topology loader. The Interface callback delegates to the loader for
+// live topology access.
+func (ec *embeddedConnector) snetTopology() snet.Topology {
+	ia := ec.topo.IA()
+	portMin, portMax := ec.topo.PortRange()
+	return snet.Topology{
+		LocalIA:   ia,
+		PortRange: snet.TopologyPortRange{Start: portMin, End: portMax},
+		Interface: func(id uint16) (netip.AddrPort, bool) {
+			ifInfoMap := ec.topo.InterfaceInfoMap()
+			info, ok := ifInfoMap[iface.ID(id)]
+			if !ok {
+				return netip.AddrPort{}, false
+			}
+			return info.InternalAddr, true
+		},
+	}
+}
+
+// Paths resolves end-to-end paths using the embedded fetcher (segment fetch + combination).
+func (ec *embeddedConnector) Paths(ctx context.Context, dst, src addr.IA, f daemon.PathReqFlags) ([]snet.Path, error) {
+	return ec.fetcher.GetPaths(ctx, src, dst, f.Refresh)
+}
+
+// ASInfo is not supported by the embedded connector.
+func (ec *embeddedConnector) ASInfo(_ context.Context, _ addr.IA) (daemon.ASInfo, error) {
+	return daemon.ASInfo{}, serrors.New("not supported by embedded connector")
+}
+
+// SVCInfo is not supported by the embedded connector.
+func (ec *embeddedConnector) SVCInfo(_ context.Context, _ []addr.SVC) (map[addr.SVC][]string, error) {
+	return nil, serrors.New("not supported by embedded connector")
+}
+
+// RevNotification is not supported by the embedded connector.
+func (ec *embeddedConnector) RevNotification(_ context.Context, _ *path_mgmt.RevInfo) error {
+	return serrors.New("not supported by embedded connector")
+}
+
+// DRKeyGetASHostKey is not supported by the embedded connector.
+func (ec *embeddedConnector) DRKeyGetASHostKey(_ context.Context, _ drkey.ASHostMeta) (drkey.ASHostKey, error) {
+	return drkey.ASHostKey{}, serrors.New("not supported by embedded connector")
+}
+
+// DRKeyGetHostASKey is not supported by the embedded connector.
+func (ec *embeddedConnector) DRKeyGetHostASKey(_ context.Context, _ drkey.HostASMeta) (drkey.HostASKey, error) {
+	return drkey.HostASKey{}, serrors.New("not supported by embedded connector")
+}
+
+// DRKeyGetHostHostKey is not supported by the embedded connector.
+func (ec *embeddedConnector) DRKeyGetHostHostKey(_ context.Context, _ drkey.HostHostMeta) (drkey.HostHostKey, error) {
+	return drkey.HostHostKey{}, serrors.New("not supported by embedded connector")
+}
+
+// Close shuts down the embedded connector, stopping the topology loader
+// and closing storage backends.
+func (ec *embeddedConnector) Close() error {
+	if ec.cancel != nil {
+		ec.cancel()
+	}
+	if ec.pathDB != nil {
+		ec.pathDB.Close()
+	}
+	if ec.revCache != nil {
+		ec.revCache.Close()
+	}
+	return nil
+}
+
+// newEmbeddedConnector creates a new embeddedConnector from a topology file.
+// It wires up the path fetcher pipeline following the daemon's own assembly
+// (daemon/cmd/daemon/main.go), but without trust verification (Phase 1).
+func newEmbeddedConnector(ctx context.Context, topoPath, stateDir string, logf logger.Logf, netMon *netmon.Monitor) (*embeddedConnector, error) {
+	// 1. Load topology.
+	topo, err := topology.NewLoader(topology.LoaderCfg{
+		File:      topoPath,
+		Validator: &topology.DefaultValidator{},
+	})
+	if err != nil {
+		return nil, fmt.Errorf("loading topology from %s: %w", topoPath, err)
+	}
+
+	// Start the topology loader in a background goroutine for reload support.
+	topoCtx, topoCancel := context.WithCancel(ctx)
+	go func() {
+		_ = topo.Run(topoCtx)
+	}()
+
+	// 2. Create storage backends.
+	if err := os.MkdirAll(stateDir, 0o700); err != nil {
+		topoCancel()
+		return nil, fmt.Errorf("creating state directory %s: %w", stateDir, err)
+	}
+
+	dbPath := filepath.Join(stateDir, "scion-pathdb.sqlite")
+	pathDB, err := storage.NewPathStorage(storage.DBConfig{Connection: dbPath})
+	if err != nil {
+		topoCancel()
+		return nil, fmt.Errorf("creating path storage at %s: %w", dbPath, err)
+	}
+
+	revCache := storage.NewRevocationStorage()
+
+	// 3. Create gRPC dialer that resolves CS addresses from the topology,
+	// using netns-aware TCP connections for cross-platform compatibility
+	// (SO_MARK on Linux, VpnService.protect on Android, IP_BOUND_IF on macOS).
+	dialer := &netnsTCPDialer{
+		SvcResolver: func(dst addr.SVC) []resolver.Address {
+			targets := []resolver.Address{}
+			for _, entry := range topo.ControlServiceAddresses() {
+				targets = append(targets, resolver.Address{Addr: entry.String()})
+			}
+			return targets
+		},
+		NetDialer: netns.NewDialer(logf, netMon).DialContext,
+	}
+
+	// 4. Create the segment fetcher requester (gRPC to local CS).
+	requester := &segfetchergrpc.Requester{
+		Dialer: dialer,
+	}
+
+	// 5. Create the path fetcher with accept-all verification (Phase 1).
+	sdCfg := config.SDConfig{}
+	sdCfg.InitDefaults()
+
+	f := fetcher.NewFetcher(fetcher.FetcherConfig{
+		IA:         topo.IA(),
+		MTU:        topo.MTU(),
+		Core:       topo.Core(),
+		NextHopper: topo,
+		RPC:        requester,
+		PathDB:     pathDB,
+		Inspector:  endHostInspector{},
+		Verifier:   acceptAllVerifier{},
+		RevCache:   revCache,
+		Cfg:        sdCfg,
+	})
+
+	return &embeddedConnector{
+		topo:     topo,
+		fetcher:  f,
+		pathDB:   pathDB,
+		revCache: revCache,
+		cancel:   topoCancel,
+	}, nil
+}
+
+// acceptAllVerifier skips segment verification. This matches the daemon's own
+// behavior when DisableSegVerification is set (daemon/cmd/daemon/main.go:359-377).
+type acceptAllVerifier struct{}
+
+func (acceptAllVerifier) Verify(_ context.Context, _ *cryptopb.SignedMessage,
+	_ ...[]byte) (*signed.Message, error) {
+	return nil, nil
+}
+
+func (v acceptAllVerifier) WithServer(_ net.Addr) infra.Verifier {
+	return v
+}
+
+func (v acceptAllVerifier) WithIA(_ addr.IA) infra.Verifier {
+	return v
+}
+
+func (v acceptAllVerifier) WithValidity(_ cppki.Validity) infra.Verifier {
+	return v
+}
+
+// endHostInspector is a minimal trust.Inspector for non-core endhosts.
+// It always reports no attributes, which is correct for endhost path resolution.
+type endHostInspector struct{}
+
+func (endHostInspector) ByAttributes(_ context.Context, _ addr.ISD, _ trust.Attribute) ([]addr.IA, error) {
+	return nil, nil
+}
+
+func (endHostInspector) HasAttributes(_ context.Context, _ addr.IA, _ trust.Attribute) (bool, error) {
+	return false, nil
+}
+
+// netnsTCPDialer implements libgrpc.Dialer with netns-aware TCP connections
+// for cross-platform socket control (SO_MARK, VpnService.protect, IP_BOUND_IF).
+type netnsTCPDialer struct {
+	SvcResolver func(addr.SVC) []resolver.Address
+	NetDialer   func(ctx context.Context, network, address string) (net.Conn, error)
+}
+
+// Compile-time interface check.
+var _ libgrpc.Dialer = (*netnsTCPDialer)(nil)
+
+func (d *netnsTCPDialer) Dial(ctx context.Context, dst net.Addr) (*grpc.ClientConn, error) {
+	opts := []grpc.DialOption{
+		grpc.WithTransportCredentials(insecure.NewCredentials()),
+		grpc.WithContextDialer(func(ctx context.Context, addr string) (net.Conn, error) {
+			return d.NetDialer(ctx, "tcp", addr)
+		}),
+		libgrpc.UnaryClientInterceptor(),
+		libgrpc.StreamClientInterceptor(),
+	}
+
+	if v, ok := dst.(*snet.SVCAddr); ok {
+		targets := d.SvcResolver(v.SVC)
+		if len(targets) == 0 {
+			return nil, serrors.New("could not resolve", "svc", v.SVC)
+		}
+		r := manual.NewBuilderWithScheme("svc")
+		r.InitialState(resolver.State{Addresses: targets})
+		opts = append(opts,
+			grpc.WithDefaultServiceConfig(`{"loadBalancingConfig": [{"round_robin":{}}]}`),
+			grpc.WithResolvers(r),
+		)
+		//nolint:staticcheck // grpc.DialContext is used by scionproto v0.14.0
+		return grpc.DialContext(ctx, r.Scheme()+":///"+v.SVC.BaseString(), opts...)
+	}
+
+	//nolint:staticcheck // grpc.DialContext is used by scionproto v0.14.0
+	return grpc.DialContext(ctx, dst.String(), opts...)
+}
+
+// scionTopologyPath returns the path to the SCION topology file, checking
+// TS_SCION_TOPOLOGY first, then the platform's SCION config directory
+// (/etc/scion/ on Linux), then a "scion" subdirectory under the tailscaled
+// state directory (for bootstrapped topologies).
+func scionTopologyPath() string {
+	if p := scionTopology(); p != "" {
+		return p
+	}
+	if runtime.GOOS == "linux" {
+		const defaultSCIONTopology = "/etc/scion/topology.json"
+		if _, err := os.Stat(defaultSCIONTopology); err == nil {
+			return defaultSCIONTopology
+		}
+	}
+	// Bootstrapped topology under the tailscaled state directory.
+	return filepath.Join(paths.DefaultTailscaledStateDir(), "scion", "topology.json")
+}
+
+// scionStateDir returns the directory for SCION state (PathDB, etc.),
+// checking TS_SCION_STATE_DIR first, then falling back to a "scion"
+// subdirectory under the platform's default tailscaled state directory.
+func scionStateDir() string {
+	if d := scionStateDirEnv(); d != "" {
+		return d
+	}
+	base := paths.DefaultTailscaledStateDir()
+	if base == "" || base == "." {
+		if appDir := paths.AppSharedDir.Load(); appDir != "" {
+			base = appDir
+		}
+	}
+	if base == "" || base == "." {
+		return ""
+	}
+	return filepath.Join(base, "scion")
+}
+
+// tryEmbeddedDaemon attempts to set up a SCION connection using the embedded
+// connector with the given topology file. This mirrors trySCIONConnect but
+// uses the embedded connector instead of an external daemon.
+func tryEmbeddedDaemon(ctx context.Context, topoPath string, logf logger.Logf, netMon *netmon.Monitor) (*scionConn, error) {
+	stateDir := scionStateDir()
+	ec, err := newEmbeddedConnector(ctx, topoPath, stateDir, logf, netMon)
+	if err != nil {
+		return nil, fmt.Errorf("creating embedded connector: %w", err)
+	}
+
+	return finishSCIONConnect(ctx, ec, ec.snetTopology(), logf, netMon)
+}
diff --git a/wgengine/netstack/netstack.go b/wgengine/netstack/netstack.go
index 59c2613451fa5..ae77a1dac1787 100644
--- a/wgengine/netstack/netstack.go
+++ b/wgengine/netstack/netstack.go
@@ -603,15 +603,25 @@ type LocalBackend = any
 
 // Start sets up all the handlers so netstack can start working. Implements
 // wgengine.FakeImpl.
+//
+// The provided LocalBackend interface can be either nil, for special case users
+// of netstack that don't have a LocalBackend, or a non-nil
+// *ipnlocal.LocalBackend. Any other type will cause Start to panic.
+//
+// Start currently (2026-03-11) never returns a non-nil error, but maybe it did
+// in the past and maybe it will in the future.
 func (ns *Impl) Start(b LocalBackend) error {
-	if b == nil {
-		panic("nil LocalBackend interface")
-	}
-	lb := b.(*ipnlocal.LocalBackend)
-	if lb == nil {
-		panic("nil LocalBackend")
+	switch b := b.(type) {
+	case nil:
+		// No backend, so just continue with ns.lb unset.
+	case *ipnlocal.LocalBackend:
+		if b == nil {
+			panic("nil LocalBackend")
+		}
+		ns.lb = b
+	default:
+		panic(fmt.Sprintf("unexpected type for LocalBackend: %T", b))
 	}
-	ns.lb = lb
 	tcpFwd := tcp.NewForwarder(ns.ipstack, tcpRXBufDefSize, maxInFlightConnectionAttempts(), ns.acceptTCP)
 	udpFwd := udp.NewForwarder(ns.ipstack, ns.acceptUDPNoICMP)
 	ns.ipstack.SetTransportProtocolHandler(tcp.ProtocolNumber, ns.wrapTCPProtocolHandler(tcpFwd.HandlePacket))
diff --git a/wgengine/userspace.go b/wgengine/userspace.go
index 705555d4446a6..ecf3c22983aa4 100644
--- a/wgengine/userspace.go
+++ b/wgengine/userspace.go
@@ -272,6 +272,13 @@ type Config struct {
 	// leave it zero, in which case a new disco key is generated per
 	// Tailscale start and kept only in memory.
 	ForceDiscoKey key.DiscoPrivate
+
+	// OnDERPRecv, if non-nil, is called for every non-disco packet
+	// received from DERP before the peer map lookup. If it returns
+	// true, the packet is considered handled and is not passed to
+	// WireGuard. The pkt slice is borrowed and must be copied if
+	// the callee needs to retain it.
+	OnDERPRecv func(regionID int, src key.NodePublic, pkt []byte) (handled bool)
 }
 
 // NewFakeUserspaceEngine returns a new userspace engine for testing.
@@ -441,6 +448,7 @@ func NewUserspaceEngine(logf logger.Logf, conf Config) (_ Engine, reterr error)
 		ControlKnobs:   conf.ControlKnobs,
 		PeerByKeyFunc:  e.PeerByKey,
 		ForceDiscoKey:  conf.ForceDiscoKey,
+		OnDERPRecv:     conf.OnDERPRecv,
 	}
 	if buildfeatures.HasLazyWG {
 		magicsockOpts.NoteRecvActivity = e.noteRecvActivity
diff --git a/wgengine/userspace_test.go b/wgengine/userspace_test.go
index b06ea527b27ba..18d870af1e6dc 100644
--- a/wgengine/userspace_test.go
+++ b/wgengine/userspace_test.go
@@ -5,6 +5,7 @@ package wgengine
 
 import (
 	"fmt"
+	"math/rand"
 	"net/netip"
 	"os"
 	"reflect"
@@ -175,8 +176,8 @@ func TestUserspaceEnginePortReconfig(t *testing.T) {
 	var ue *userspaceEngine
 	ht := health.NewTracker(bus)
 	reg := new(usermetric.Registry)
-	for i := range 100 {
-		attempt := uint16(defaultPort + i)
+	for range 100 {
+		attempt := uint16(defaultPort + rand.Intn(1000))
 		e, err := NewFakeUserspaceEngine(t.Logf, attempt, &knobs, ht, reg, bus)
 		if err != nil {
 			t.Fatal(err)