persistence

# Persistence ## Read First - `src/lib/db.ts` for the current Dexie version and upgrade history. - `src/store/store.ts` for debounced position/full saves and state initialization. - `src/lib/backup.ts` for `.thot` export/import behavior. - `src/lib/types.ts` for persisted shapes. ## Change Rules 1. Treat `src/lib/db.ts` as an append-only schema history. Add a new `version()` for persisted schema/index changes; do not rewrite old migrations. 2. Add upgrade logic for old records when a new required field cannot be safely defaulted at read time. 3. Preserve existing debounce and transaction behavior. Account for the fact that an immediate IndexedDB read after a mutation can observe the previous value. 4. Check all lifecycle paths for changed fields: create, import, duplicate, trash, restore, permanent delete, checkpoint, backup export, and backup import. 5. Keep `diagrams` and `diagramsMap` synchronized in Zustand. Avoid direct partial state updates that leave the map stale. 6. If a change affects backups, update validation and date rehydration deliberately. Backups currently cover diagrams, selected diagram state, and AI chat sessions, not every local table. 7. Use Dexie transactions for multi-table replacement or clear-and-restore operations. ## Verification - Test a fresh database and representative existing records when adding a migration. - Verify reload persistence after normal edits, position-only edits, imports, restores, and deletion. - Check backup round trips and confirm invalid backup input does not partially replace local data. - Run `pnpm run type-check`, `pnpm run lint`, and `pnpm run build`.