chore: add architecture lint guardrails (#2168)

.github/workflows/architecture-lint.yml

@@ -0,0 +1,50 @@
+name: Architecture Lint
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+concurrency:
+  # Pull requests can supersede one another safely. Pushes compare each commit
+  # with its own before-SHA, so never cancel a push run before that comparison
+  # completes.
+  group: ${{ github.workflow }}-${{ github.event_name == 'pull_request' && github.ref || github.sha }}
+  cancel-in-progress: ${{ github.event_name == 'pull_request' }}
+
+permissions:
+  contents: read
+
+jobs:
+  lint:
+    name: Architecture boundaries do not regress
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6
+        with:
+          fetch-depth: 0
+          persist-credentials: false
+
+      - name: Run linter tests
+        run: python3 scripts/lint-architecture.test.py
+
+      - name: Lint pull request architecture
+        if: github.event_name == 'pull_request'
+        env:
+          ARCHITECTURE_BASE_REF: ${{ github.event.pull_request.base.sha }}
+        run: >-
+          python3 scripts/lint-architecture.py --all
+          --baseline-base-ref "$ARCHITECTURE_BASE_REF"
+          --allow-missing-base-baseline
+
+      - name: Lint pushed architecture
+        if: github.event_name == 'push'
+        env:
+          ARCHITECTURE_BASE_REF: ${{ github.event.before }}
+        run: >-
+          python3 scripts/lint-architecture.py --all
+          --baseline-base-ref "$ARCHITECTURE_BASE_REF"
+          --allow-missing-base-baseline