diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index fb936826..6196fc50 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -188,9 +188,9 @@ jobs:
       # ------------------------------------------------------------------
       # 4. Header-only externals (Eigen, Boost, CGAL, fmt, pybind11, ...)
       # ------------------------------------------------------------------
-      - name: Cache header-only externals
+      - name: Restore header-only externals cache
         id: cache-headeronlys
-        uses: actions/cache@v4
+        uses: actions/cache/restore@v4
         with:
           path: |
             external/argparse
@@ -214,12 +214,32 @@ jobs:
           curl -L -o external/external_headeronlys.tar.gz "$HEADERONLYS_URL"
           cd external && tar -xzf external_headeronlys.tar.gz
 
+      - name: Save header-only externals cache
+        if: always()
+        uses: actions/cache/save@v4
+        with:
+          path: |
+            external/argparse
+            external/boost
+            external/CGAL
+            external/cppcodec
+            external/cpptrace
+            external/doctest
+            external/eigen
+            external/exprtk
+            external/fmt
+            external/nanoflann
+            external/nlohmann
+            external/pybind11
+            external/pybind11_json
+          key: headeronlys-v1
+
       # ------------------------------------------------------------------
       # 5. cfd_externals (zlib, hdf5, cgns, parmetis)
       # ------------------------------------------------------------------
-      - name: Cache cfd_externals install
+      - name: Restore cfd_externals cache
         id: cache-cfd-ext
-        uses: actions/cache@v4
+        uses: actions/cache/restore@v4
         with:
           path: external/cfd_externals/install
           key: cfd-ext-${{ runner.os }}-${{ steps.submod.outputs.cfd_ext_sha }}
@@ -227,16 +247,29 @@ jobs:
       - name: Build cfd_externals
         if: steps.cache-cfd-ext.outputs.cache-hit != 'true'
         run: |
+          # Double-check: skip if install already restored via prefix match
+          if [ -f external/cfd_externals/install/lib/libcgns.a ]; then
+            echo "cfd_externals install present (cache prefix match), skipping build"
+            exit 0
+          fi
+          rm -rf external/cfd_externals
           git submodule update --init --recursive --depth=1
           cd external/cfd_externals
           CC=mpicc CXX=mpicxx python3 cfd_externals_build.py
 
+      - name: Save cfd_externals cache
+        if: always()
+        uses: actions/cache/save@v4
+        with:
+          path: external/cfd_externals/install
+          key: cfd-ext-${{ runner.os }}-${{ steps.submod.outputs.cfd_ext_sha }}
+
       # ------------------------------------------------------------------
       # 6. Python venv
       # ------------------------------------------------------------------
-      - name: Cache Python venv
+      - name: Restore Python venv cache
         id: cache-venv
-        uses: actions/cache@v4
+        uses: actions/cache/restore@v4
         with:
           path: venv
           key: venv-ci-${{ runner.os }}-${{ steps.submod.outputs.cfd_ext_sha }}-${{ hashFiles('requirements.txt', 'scripts/install_python_deps.sh') }}
@@ -249,6 +282,13 @@ jobs:
           pip install --upgrade pip
           PIP=$PWD/venv/bin/pip ./scripts/install_python_deps.sh
 
+      - name: Save Python venv cache
+        if: always()
+        uses: actions/cache/save@v4
+        with:
+          path: venv
+          key: venv-ci-${{ runner.os }}-${{ steps.submod.outputs.cfd_ext_sha }}-${{ hashFiles('requirements.txt', 'scripts/install_python_deps.sh') }}
+
       # ------------------------------------------------------------------
       # 7. ccache
       # ------------------------------------------------------------------
diff --git a/AGENTS.md b/AGENTS.md
index 261e8a33..173d13ad 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -333,8 +333,19 @@ Key concepts agents should know:
 **Read-only by default.** You may use `gh` freely for read operations (viewing
 issues, PRs, checks, releases, diffs, comments). **Do NOT use `gh` for any
 write operation** (creating/closing issues, creating/merging PRs, posting
-comments, approving reviews, creating releases, editing labels, etc.) **unless
-the user explicitly requests that specific write action.** One-time explicit
-permission does not carry over to other write actions — ask each time.
+comments, approving reviews, creating releases, editing labels, deleting
+caches, etc.) **unless the user explicitly requests that specific write
+action.** One-time explicit permission does not carry over to other write
+actions — ask each time.
+
+**Operations requiring explicit user authorization (non-exhaustive):**
+- `gh pr create/merge/close/edit`
+- `gh issue create/close/edit`
+- `gh pr comment` / `gh issue comment`
+- `gh pr review`
+- `gh release create/delete`
+- `gh cache delete`
+- `gh api` with non-GET methods (POST, PUT, PATCH, DELETE)
+- `git push --force` / `git push --force-with-lease`
 
 **Draft PR by default** You must use --draft on new prs.