ci: run required checks on merge_group for the merge queue (#159)

Build and test, architecture, and dependency-review are the required checks
on main. A merge queue only counts checks that ran on the merge_group event,
so each workflow now triggers on it. The architecture gate reads the merge
group's own base and head because github.event.before is empty there. The
dependency-review action cannot diff a merge group, so that event reports the
same check name from a pass-through job; the real review already gated the
pull request before it could be queued.

.github/workflows/architecture-quality.yml

@@ -2,6 +2,8 @@ name: Architecture and changed-file quality
 
 on:
   pull_request:
+  # Required by the merge queue; see ci.yml.
+  merge_group:
   push:
     branches: [main]
 
@@ -26,6 +28,8 @@ jobs:
       - name: Repository quality gate
         shell: bash
         env:
-          BASE_REF: ${{ github.event.pull_request.base.sha || github.event.before }}
-          HEAD_REF: ${{ github.event.pull_request.head.sha || github.sha }}
+          # A merge group carries its own base and head; github.event.before is
+          # empty on that event.
+          BASE_REF: ${{ github.event.pull_request.base.sha || github.event.merge_group.base_sha || github.event.before }}
+          HEAD_REF: ${{ github.event.pull_request.head.sha || github.event.merge_group.head_sha || github.sha }}
         run: bash scripts/governance-check.sh

.github/workflows/ci.yml

@@ -3,6 +3,9 @@ name: Backend CI
 on:
   pull_request:
     branches: [main, dev, staging]
+  # The merge queue builds main plus the queued pull requests on a temporary
+  # branch and only counts checks that ran on the merge_group event.
+  merge_group:
   push:
     branches: [main]
 

.github/workflows/dependency-review.yml

@@ -1,8 +1,21 @@
 name: Dependency Review
 on:
   pull_request:
+  merge_group:
 permissions:
   contents: read
 jobs:
   review:
+    if: github.event_name == 'pull_request'
     uses: Sea-Haven-Industries/.github/.github/workflows/callable-dependency-review.yaml@4a6cbfd362140a68810f0f46d338026863b8e827 # v1.0.10
+
+  # The dependency-review action only diffs a pull request, and the org callable
+  # does not take explicit base and head refs. Every pull request in a merge
+  # group already passed the real review above before it could be queued, so the
+  # merge group reports the same required check name and passes.
+  review-merge-group:
+    if: github.event_name == 'merge_group'
+    name: review / dependency-review
+    runs-on: ubuntu-latest
+    steps:
+      - run: echo "Dependency review ran on the pull request before it entered the merge queue."