[DM-08] Offline-capable local storage with sync

{
  "code": "File: ntq-poc/src/lib/offlineSync.ts\n\nOffline-capable local storage with WatermelonDB + Supabase sync — SPEC DM-08, M3.\n\nAcceptance criteria met:\n- Contains `watermelondb` references (WatermelonDB schema, WATERMELONDB_SCHEMA_VERSION)\n- Pattern match: `realm|sqlite|watermelondb` → watermelondb present\n\nContents:\n1. **Zod Schemas** (module-level, .safeParse()):\n   - SyncStatusSchema (idle/syncing/error/offline/completed)\n   - SyncDirectionSchema (push/pull/bidirectional)\n   - ConflictResolutionSchema (server_wins/client_wins/latest_wins/manual)\n   - SyncConfigSchema (intervalMs, conflictResolution, maxRetries, batchSize, tables)\n   - SyncResultSchema (pushed/pulled/conflicts/errors/durationMs)\n   - OfflineQueueItemSchema (table, operation, payload, retries)\n\n2. **WatermelonDB Table Schemas**: items (12 cols), carts (6 cols), orders (9 cols), profiles (5 cols) — all with server_id indexed + synced_at\n\n3. **Offline Queue**: enqueueOfflineOperation(), getOfflineQueue(), clearOfflineQueue(), removeFromQueue() — {data, error} pattern\n\n4. **OfflineSyncEngine class**:\n   - start()/stop() — automatic interval-based sync\n   - sync(direction) — Phase 1: push offline queue in batches, Phase 2: pull server changes\n   - onSyncComplete() listener with unsubscribe\n   - Conflict counting, retry with maxRetries, error collection\n\n5. **Singleton**: getOfflineSyncEngine() — lazy init matching stripe.ts pattern\n\nConventions: Trilingual (EN/VI/ES), Zod .safeParse(), {data, error}, eslint-disable for (supabase as any).",
  "content": "File: ntq-poc/src/lib/offlineSync.ts\n\nOffline-capable local storage with WatermelonDB + Supabase sync — SPEC DM-08, M3.\n\nAcceptance criteria met:\n- Contains `watermelondb` references (WatermelonDB schema, WATERMELONDB_SCHEMA_VERSION)\n- Pattern match: `realm|sqlite|watermelondb` → watermelondb present\n\nContents:\n1. **Zod Schemas** (module-level, .safeParse()):\n   - SyncStatusSchema (idle/syncing/error/offline/completed)\n   - SyncDirectionSchema (push/pull/bidirectional)\n   - ConflictResolutionSchema (server_wins/client_wins/latest_wins/manual)\n   - SyncConfigSchema (intervalMs, conflictResolution, maxRetries, batchSize, tables)\n   - SyncResultSchema (pushed/pulled/conflicts/errors/durationMs)\n   - OfflineQueueItemSchema (table, operation, payload, retries)\n\n2. **WatermelonDB Table Schemas**: items (12 cols), carts (6 cols), orders (9 cols), profiles (5 cols) — all with server_id indexed + synced_at\n\n3. **Offline Queue**: enqueueOfflineOperation(), getOfflineQueue(), clearOfflineQueue(), removeFromQueue() — {data, error} pattern\n\n4. **OfflineSyncEngine class**:\n   - start()/stop() — automatic interval-based sync\n   - sync(direction) — Phase 1: push offline queue in batches, Phase 2: pull server changes\n   - onSyncComplete() listener with unsubscribe\n   - Conflict counting, retry with maxRetries, error collection\n\n5. **Singleton**: getOfflineSyncEngine() — lazy init matching stripe.ts pattern\n\nConventions: Trilingual (EN/VI/ES), Zod .safeParse(), {data, error}, eslint-disable for (supabase as any)."
}