ci: split workflows and move pnpm lockfile ownership to GitHub Actions

.github/workflows/pr-policy.yml

@@ -0,0 +1,49 @@
+name: PR Policy
+
+on:
+  pull_request:
+    branches:
+      - master
+
+concurrency:
+  group: pr-policy-${{ github.event.pull_request.number }}
+  cancel-in-progress: true
+
+jobs:
+  policy:
+    runs-on: ubuntu-latest
+    timeout-minutes: 10
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+
+      - name: Setup pnpm
+        uses: pnpm/action-setup@v4
+        with:
+          version: 9.15.4
+          run_install: false
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: 20
+          cache: pnpm
+
+      - name: Block manual lockfile edits
+        run: |
+          changed="$(git diff --name-only "${{ github.event.pull_request.base.sha }}" "${{ github.event.pull_request.head.sha }}")"
+          if printf '%s\n' "$changed" | grep -qx 'pnpm-lock.yaml'; then
+            echo "Do not commit pnpm-lock.yaml in pull requests. CI owns lockfile updates."
+            exit 1
+          fi
+
+      - name: Validate dependency resolution when manifests change
+        run: |
+          changed="$(git diff --name-only "${{ github.event.pull_request.base.sha }}" "${{ github.event.pull_request.head.sha }}")"
+          manifest_pattern='(^|/)package\.json$|^pnpm-workspace\.yaml$|^\.npmrc$|^pnpmfile\.(cjs|js|mjs)$'
+          if printf '%s\n' "$changed" | grep -Eq "$manifest_pattern"; then
+            pnpm install --lockfile-only --ignore-scripts --no-frozen-lockfile
+          fi