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Closes #4222. Three changes that together stabilize Readest sync across devices: **Stop the artificial updatedAt bump in useProgressAutoSave** saveConfig unconditionally bumps config.updatedAt = Date.now(), and useProgressAutoSave used to fire saveConfig on the very first relocate after book open — even though that relocate just reflects the position loaded from disk, not user action. The stale local config then looked "newer" than a fresher server-side push, so the next auto-push overwrote the other device's real progress via last-writer-wins. The hook now snapshots the loaded location and skips saveConfig when the in-memory location still matches it. **Retry the first config pull with backoff + release the gate** useProgressSync gates pushes behind a successful pull (so a brand-new import can't clobber the server's real progress). But handleAutoSync only re-arms on progress.location changes, so a single failed pull (Android cold-start contention, Wi-Fi/LTE handoff, captive portal) used to block every push for the whole reader session. The new pullWithRetry retries on backoff (1500/4000/10000 ms) and releases the gate after exhaustion — server-side last-writer-wins still protects the cross-device case (a stale local push with an older updated_at loses to a fresher server record). sync-book-progress events reset the chain so manual pull-to-refresh recovers cleanly. Fetch timeout bumped from 8s to 15s to better tolerate slow networks in that cold-start window. **Server piggybacks books.progress off configs push** /api/sync POST now updates books.progress + books.updated_at for each upserted config, gated by .lt('updated_at') so a concurrent newer books push is never downgraded and a missing row is a silent no-op (useBooksSync still seeds new rows from the library page). The in-reader syncBooks round-trip is dropped — the reader now sends one POST per auto-save instead of two, and the books row stays consistent with config pushes even while a reader stays open (#4198). Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>