fix: enforce durable migration ownership and readiness

tests/test_postgres_store.py

@@ -89,6 +89,22 @@ def test_postgresql_readiness_fails_when_database_is_unavailable() -> None:
     asyncio.run(store.aclose())
 
 
+def test_postgresql_readiness_fails_when_runtime_tables_are_unavailable(tmp_path) -> None:
+    database_url = f"sqlite+aiosqlite:///{tmp_path / 'empty.db'}"
+    store = PostgresPortStore.from_url(database_url)
+    settings = RuntimeSettings(
+        environment="production",
+        backend="postgresql",
+        allow_ephemeral=False,
+        database_url=database_url,
+    )
+    response = TestClient(create_app(settings=settings, port_store=store)).get("/readyz")
+
+    assert response.status_code == 503
+    assert response.json()["checks"]["database"] == "unavailable"
+    asyncio.run(store.aclose())
+
+
 def _event(event_type: str) -> dict:
     return {
         "schema_version": "0.1.0",