ci: add main-push-audit tripwire

.github/workflows/main-push-audit.yml

@@ -0,0 +1,62 @@
+name: Audit — Direct push to main
+
+# Tripwire: fires on every push to main and flags pushes that did not come
+# from a merged PR. Branch protection is enforced at the repo level, but this
+# provides a soft audit trail for any direct pushes (e.g. emergency hotfixes).
+#
+# Behavior:
+#   - If the pushed commit is associated with a merged PR, exit quietly.
+#   - If not, open a GitHub issue tagging the pusher so it's visible.
+#
+# This never blocks the push. It's an audit, not a gate.
+
+on:
+  push:
+    branches: [main]
+
+permissions:
+  contents: read
+  issues: write
+  pull-requests: read
+
+jobs:
+  audit:
+    name: Check commit came from PR
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check for associated PR
+        uses: actions/github-script@v7
+        with:
+          script: |
+            const sha = context.sha;
+            const { data: prs } = await github.rest.repos.listPullRequestsAssociatedWithCommit({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              commit_sha: sha,
+            });
+            const merged = prs.find(p => p.merged_at);
+            if (merged) {
+              core.info(`OK: commit ${sha.substring(0,7)} came from PR #${merged.number}`);
+              return;
+            }
+            const pusher = context.payload.pusher?.name || context.actor;
+            const msg = context.payload.head_commit?.message?.split('\n')[0] || '(no message)';
+            const body = [
+              `**Direct push to \`main\` detected** — commit was not associated with a merged PR.`,
+              ``,
+              `- Commit: \`${sha.substring(0,7)}\` — ${msg}`,
+              `- Pusher: @${pusher}`,
+              `- Workflow run: ${context.serverUrl}/${context.repo.owner}/${context.repo.repo}/actions/runs/${context.runId}`,
+              ``,
+              `The project policy is that all changes to \`main\` go through a pull request so they can be reviewed before deploying to production. If this push was intentional (hotfix, infra change) close this issue with a comment explaining why.`,
+              ``,
+              `_This issue was opened automatically by \`.github/workflows/main-push-audit.yml\`._`,
+            ].join('\n');
+            await github.rest.issues.create({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              title: `Direct push to main: ${sha.substring(0,7)}`,
+              body,
+              labels: ['policy-violation', 'audit'],
+            });
+            core.warning(`Opened audit issue for direct push ${sha.substring(0,7)}`);