chore(stack): reconcile availability probes with #270

.github/workflows/ci.yml

@@ -3,8 +3,9 @@ name: CI
 on:
   push:
     branches: [main]
-  pull_request:
-    branches: [main]
+  # Every pull request target, including immutable stack branches, receives the
+  # same exact-head, synthetic-merge, and buyer-readiness acceptance evidence.
+  pull_request: {}
 
 permissions:
   contents: read

scripts/test_ci_workflow_stack_coverage.py

@@ -0,0 +1,33 @@
+"""Verify that stacked pull requests retain the complete CI acceptance contract."""
+
+from pathlib import Path
+import unittest
+
+
+REPOSITORY_ROOT = Path(__file__).resolve().parents[1]
+CI_WORKFLOW = REPOSITORY_ROOT / ".github" / "workflows" / "ci.yml"
+
+
+class CiWorkflowStackCoverageTest(unittest.TestCase):
+    """Exercises the stacked-pull-request workflow contract with standard discovery."""
+
+    def test_ci_runs_for_every_pull_request_base(self) -> None:
+        """Stacked pull requests must receive the same exact-head CI as main-bound PRs."""
+        workflow = CI_WORKFLOW.read_text(encoding="utf-8")
+
+        self.assertIn("  pull_request: {}", workflow)
+        self.assertNotIn("  pull_request:\n    branches: [main]", workflow)
+
+    def test_ci_preserves_exact_head_and_synthetic_merge_evidence(self) -> None:
+        """Broadening PR coverage must not weaken exact-head or merge verification."""
+        workflow = CI_WORKFLOW.read_text(encoding="utf-8")
+
+        exact_head_expression = "github.event.pull_request.head.sha || github.sha"
+        self.assertGreaterEqual(workflow.count(exact_head_expression), 4)
+        self.assertIn('test "$(git rev-parse HEAD)" = "$EXPECTED_SHA"', workflow)
+        self.assertIn("name: Maven merge compatibility", workflow)
+        self.assertIn("name: Buyer-readiness script tests", workflow)
+
+
+if __name__ == "__main__":
+    unittest.main()