ci: add umbra-reviewer advisory review + Dependabot

.github/dependabot.yml

@@ -0,0 +1,6 @@
+version: 2
+updates:
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "weekly"

.github/workflows/reviewer.yml

@@ -0,0 +1,70 @@
+name: Reviewer
+
+# Advisory PR review (umbra-reviewer): surfaces architecture + security issues
+# and posts one recommendation comment. Advisory only — it never merges and never
+# fails the PR. Changes to security-sensitive surfaces (workflows, packaging) are
+# escalated to a human. See https://github.com/bkd-dotcom/umbra-reviewer
+on:
+  pull_request:
+
+permissions:
+  contents: read
+  pull-requests: write
+  checks: read
+
+jobs:
+  review:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+      - uses: actions/setup-python@v5
+        with:
+          python-version: "3.12"
+      - name: Install umbra-reviewer
+        run: pip install "umbra-reviewer>=0.1.0"
+      - name: Compute the PR diff
+        env:
+          BASE_SHA: ${{ github.event.pull_request.base.sha }}
+          HEAD_SHA: ${{ github.event.pull_request.head.sha }}
+        run: |
+          set -euo pipefail
+          git fetch --no-tags origin "$BASE_SHA" "$HEAD_SHA" 2>/dev/null || true
+          echo "OUT=${RUNNER_TEMP:-/tmp}/rev" >> "$GITHUB_ENV"
+          mkdir -p "${RUNNER_TEMP:-/tmp}/rev"
+          git diff "$BASE_SHA" "$HEAD_SHA" > "${RUNNER_TEMP:-/tmp}/rev/pr.diff"
+      - name: Run the advisory review
+        env:
+          PR: ${{ github.event.pull_request.number }}
+        run: |
+          set -uo pipefail
+          umbra-reviewer review \
+            --diff "$OUT/pr.diff" \
+            --repo "$GITHUB_REPOSITORY" \
+            --pr "$PR" \
+            --required-check unknown \
+            --protected ".github/workflows/*,.github/actions/**,action.yml,pyproject.toml" \
+            --comment-out "$OUT/comment.md" \
+            --json-out "$OUT/review.json"
+          exit 0
+      - name: Post / update the review comment
+        if: always()
+        uses: actions/github-script@v7
+        with:
+          script: |
+            const fs = require('fs'); const path = require('path');
+            const out = process.env.OUT || '';
+            let body = 'Umbra Reviewer: no review was produced.';
+            try { body = fs.readFileSync(path.join(out, 'comment.md'), 'utf8'); } catch (e) {}
+            const marker = '<!-- umbra-reviewer -->';
+            body = marker + '\n' + body;
+            const { owner, repo } = context.repo;
+            const issue_number = context.issue.number;
+            const comments = await github.rest.issues.listComments({ owner, repo, issue_number });
+            const mine = comments.data.find(c => c.body && c.body.includes(marker));
+            if (mine) {
+              await github.rest.issues.updateComment({ owner, repo, comment_id: mine.id, body });
+            } else {
+              await github.rest.issues.createComment({ owner, repo, issue_number, body });
+            }