ci: guard sample-catalog.json against manual edits

Add a pull_request check that fails any PR modifying samples/hosted-agent/sample-catalog.json unless it originates from a Sync Sample Catalog branch (ci/sync-sample-catalog-*). The catalog is a generated artifact and must only be updated by CI.

Enforcement requires marking guard-catalog as a required status check and disallowing direct pushes on the protected branch.

Author: Yimin-Jin

.github/workflows/guard-sample-catalog.yml

@@ -0,0 +1,55 @@
+name: Guard Generated Catalog
+
+# samples/hosted-agent/sample-catalog.json is GENERATED by the "Sync Sample
+# Catalog" workflow and must never be edited or committed by hand. This check
+# fails any PR that modifies it unless the PR originates from a sync-workflow
+# branch (ci/sync-sample-catalog-*).
+#
+# For this to ENFORCE (not merely report), the protected branch must also:
+#   - mark the "guard-catalog" check as a REQUIRED status check, and
+#   - disallow direct pushes (PRs only) — a pull_request guard cannot catch a
+#     direct push.
+#
+# A pull_request workflow only guards PRs targeting the branch it lives on, so
+# this file must exist on every protected branch you want covered.
+
+on:
+  pull_request:
+
+permissions:
+  contents: read
+
+jobs:
+  guard-catalog:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+
+      - name: Reject manual edits to sample-catalog.json
+        env:
+          HEAD_REF: ${{ github.head_ref }}
+          BASE_SHA: ${{ github.event.pull_request.base.sha }}
+          HEAD_SHA: ${{ github.event.pull_request.head.sha }}
+        shell: bash
+        run: |
+          set -euo pipefail
+          CATALOG="samples/hosted-agent/sample-catalog.json"
+
+          # Did this PR change the generated catalog at all?
+          if git diff --quiet "$BASE_SHA" "$HEAD_SHA" -- "$CATALOG"; then
+            echo "PR does not touch $CATALOG — OK."
+            exit 0
+          fi
+
+          # It did. Only the Sync Sample Catalog workflow (which opens PRs from
+          # ci/sync-sample-catalog-* branches) is allowed to change it.
+          if [[ "$HEAD_REF" == ci/sync-sample-catalog-* ]]; then
+            echo "Change to $CATALOG came from sync branch '$HEAD_REF' — OK."
+            exit 0
+          fi
+
+          echo "::error file=$CATALOG::$CATALOG is generated by the 'Sync Sample Catalog' workflow and must not be edited or committed manually. Revert your changes to this file; CI will regenerate it."
+          exit 1