How do you handle offline sync for mobile apps?

Offline sync depends on what data the mobile app needs offline. For read mostly workflows (catalogs, listings, content), the mobile client caches API responses with cache-control headers and ETags. For read write workflows (note taking, field work, offline orders), we implement a sync protocol with conflict resolution policies (last write wins, client wins, or three way merge). Changes queued on the device are batched and sent when connectivity returns, with idempotency keys preventing duplicates. We also integrate platform native solutions like WatermelonDB or Realm where appropriate.