Prepare API default branch protection (#311)

Add a stable Required CI gate, branch-protection desired state, and publishing runbook.

.github/workflows/tests.yml

@@ -3,6 +3,18 @@ name: Tests
 on:
   pull_request:
   push:
+    branches:
+      - master
+      - beta
+      - canary
+      - internal
+
+permissions:
+  contents: read
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event_name == 'pull_request' && github.event.pull_request.number || github.run_id }}
+  cancel-in-progress: ${{ github.event_name == 'pull_request' }}
 
 jobs:
   php:
@@ -336,11 +348,42 @@ jobs:
         if: always()
         run: docker compose -f docker-compose.yml -f .github/docker-compose.ci.yml down -v
 
+  required-ci:
+    name: Required CI
+    runs-on: ubuntu-latest
+    needs: [php, edge-agent, edge-broker, edge-gateway-backend]
+    if: ${{ always() }}
+
+    steps:
+      - name: Verify required jobs succeeded
+        env:
+          PHP_RESULT: ${{ needs.php.result }}
+          EDGE_AGENT_RESULT: ${{ needs.edge-agent.result }}
+          EDGE_BROKER_RESULT: ${{ needs.edge-broker.result }}
+          EDGE_GATEWAY_BACKEND_RESULT: ${{ needs.edge-gateway-backend.result }}
+        run: |
+          set -euo pipefail
+          failed=0
+          for dependency in \
+            "php=${PHP_RESULT}" \
+            "edge-agent=${EDGE_AGENT_RESULT}" \
+            "edge-broker=${EDGE_BROKER_RESULT}" \
+            "edge-gateway-backend=${EDGE_GATEWAY_BACKEND_RESULT}"
+          do
+            name="${dependency%%=*}"
+            result="${dependency#*=}"
+            if [ "$result" != "success" ]; then
+              echo "Required dependency ${name} completed with result: ${result:-missing}" >&2
+              failed=1
+            fi
+          done
+          test "$failed" -eq 0
+
   release-manager-gate:
     name: Release Manager gate
     runs-on: [self-hosted, Linux, X64, pleno, backend]
-    needs: [php, edge-agent, edge-broker, edge-gateway-backend]
-    if: ${{ github.event_name == 'push' && github.ref == 'refs/heads/master' }}
+    needs: [required-ci]
+    if: ${{ github.event_name == 'push' && github.ref == 'refs/heads/master' && needs.required-ci.result == 'success' }}
 
     steps:
       - name: Record Release Manager API gate