scripts(changelog): single-source changelog nav rendering

.github/workflows/changelog-check.yml

@@ -0,0 +1,23 @@
+name: Changelog nav check
+
+on:
+  pull_request:
+    paths:
+      - 'changelog/**'
+      - 'docs.json'
+      - 'merge-queue/changelog.mdx'
+      - 'flaky-tests/changelog.mdx'
+      - 'scripts/sync-changelog.py'
+
+jobs:
+  check-sync:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-python@v5
+        with:
+          python-version: '3.12'
+
+      - name: Check changelog nav is in sync
+        run: python3 scripts/sync-changelog.py --check

.github/workflows/changelog-sync.yml

@@ -0,0 +1,37 @@
+name: Changelog nav sync
+
+on:
+  push:
+    branches: [main]
+    paths:
+      - 'changelog/**'
+
+permissions:
+  contents: write
+
+jobs:
+  sync:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-python@v5
+        with:
+          python-version: '3.12'
+
+      - name: Run changelog sync
+        run: python3 scripts/sync-changelog.py
+
+      - name: Check for changes
+        id: diff
+        run: |
+          git diff --quiet && echo "changed=false" >> "$GITHUB_OUTPUT" || echo "changed=true" >> "$GITHUB_OUTPUT"
+
+      - name: Commit and push
+        if: steps.diff.outputs.changed == 'true'
+        run: |
+          git config user.name "github-actions[bot]"
+          git config user.email "41898282+github-actions[bot]@users.noreply.github.com"
+          git add docs.json changelog/index.mdx merge-queue/changelog.mdx flaky-tests/changelog.mdx
+          git commit -m "chore(changelog): sync nav from changelog entries"
+          git push

.gitignore

@@ -1 +1,2 @@
-*.py
+*.py
+!scripts/*.py

README.md

@@ -80,6 +80,23 @@ Sticky labels that mark how a PR was sourced or where it needs extra eyes. Addit
 
 GitHub's default labels (`bug`, `documentation`, `enhancement`, etc.) are also present but not used in our automated workflows.
 
+## Changelog automation
+
+Changelog entries live in `changelog/*.mdx`. Each entry's frontmatter (`title`, `description`, `date`, `category`, `type`) is the single source of truth — the nav sidebar, master index, and product-page indexes are all generated from it.
+
+### Adding a changelog entry
+
+1. Create `changelog/YYYY-MM-DD-<slug>.mdx` with the required frontmatter.
+2. Run `python3 scripts/sync-changelog.py` to regenerate the four nav files.
+3. Commit both the new entry and the updated nav files.
+
+### CI enforcement
+
+Two GitHub Actions workflows keep things in sync:
+
+- **`changelog-check.yml`** runs on PRs that touch changelog-related files. It calls `sync-changelog.py --check`, which exits non-zero if the nav files don't match what the entries would generate. If this check fails, run the sync script locally and push the result.
+- **`changelog-sync.yml`** runs on pushes to `main`. If a changelog entry landed without the nav files being regenerated, the action auto-commits the fix. This is a safety net — the PR check should catch drift before merge.
+
 ## Need help?
 
 ### Troubleshooting