# Lesson 3 complete; primaries still deferred

Learner finished lesson 3 (workers & sync access handles) with **5/5 quiz**. Demonstrated: dedicated-worker-only path, exclusive lock until `close()`, buffers + flush, main-thread `createWritable` as default, export via main-thread copy not move. External primaries (web.dev OPFS worker section; MDN FileSystemSyncAccessHandle) remain unread. Next ZPD: deal-breakers — quota/eviction/persistence, wrong-tool traps, multi-tab locks, “not multi-device truth”; do not re-teach the sync method map from zero.