fix(api): reject stale alert cache on hard failure

apps/api/tests/test_awooop_operator_timeline_labels.py

@@ -1302,6 +1302,9 @@ def test_ai_alert_card_source_unavailable_response_exposes_ai_repair_queue() ->
 async def test_list_ai_alert_card_delivery_readback_failsofts_db_unavailable(
     monkeypatch: pytest.MonkeyPatch,
 ) -> None:
+    async def stale_cache(**_kwargs):
+        return {"total": 1, "learning_registry": {}}
+
     class FailingDbContext:
         async def __aenter__(self):
             raise RuntimeError("db unavailable")
@@ -1319,6 +1322,11 @@ async def test_list_ai_alert_card_delivery_readback_failsofts_db_unavailable(
         "_load_ai_alert_card_delivery_readback_direct",
         _no_ai_alert_card_direct_readback,
     )
+    monkeypatch.setattr(
+        platform_operator_service,
+        "_get_cached_ai_alert_card_delivery_readback",
+        stale_cache,
+    )
 
     payload = await platform_operator_service.list_ai_alert_card_delivery_readback(
         project_id="awoooi",