feat: upgrade toolchain and soften sync recovery after network blips

Bump Vite 8, matrix-js-sdk, and related deps; fix immer/vanilla-extract imports for new majors. Replace blocking sync error dialog with background recovery on wake/offline, and disable Vite auto-open in dev. Add feature handoff documentation index.

docs/handoff/features/state-management/HANDOFF.md

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+# State management — handoff
+
+## Summary
+
+Client UI state uses **Jotai** atoms: room lists, unread counts, settings, modals, drafts, navigation memory, and sidebar collapse. Many atoms sync to localStorage via `atomWithLocalStorage`.
+
+## User-facing behavior
+
+- Room list order, collapsed categories, sidebar folders persist across sessions
+- Message drafts and upload queues per room persist locally
+- Settings (theme, emoji style, zoom) persist locally
+- Unread badges drive favicon and sidebar indicators
+
+## Architecture
+
+```
+JotaiProvider (App.tsx)
+  → atoms in state/
+  → hooks in state/hooks/ wrap atoms for components
+ClientBindAtoms.tsx binds Matrix events → atom updates
+```
+
+## Key files
+
+| Path | Role |
+|------|------|
+| `cinny/src/app/state/settings.ts` | User settings atom |
+| `cinny/src/app/state/sessions.ts` | Auth sessions |
+| `cinny/src/app/state/room-list/roomList.ts` | `allRoomsAtom`, ordering |
+| `cinny/src/app/state/room/roomToUnread.ts` | Unread counts |
+| `cinny/src/app/state/room/roomInputDrafts.ts` | Composer drafts + uploads |
+| `cinny/src/app/state/room/roomToParents.ts` | Space parent mapping |
+| `cinny/src/app/state/mDirectList.ts` | Direct message index |
+| `cinny/src/app/state/navToActivePath.ts` | Last active path per context |
+| `cinny/src/app/state/closedNavCategories.ts` | Collapsed nav sections |
+| `cinny/src/app/state/closedLobbyCategories.ts` | Collapsed lobby categories |
+| `cinny/src/app/state/createRoomModal.ts` | Create room modal state |
+| `cinny/src/app/state/createSpaceModal.ts` | Create space modal state |
+| `cinny/src/app/state/searchModal.ts` | Global search modal |
+| `cinny/src/app/state/utils/atomWithLocalStorage.ts` | Persistence helper |
+| `cinny/src/app/pages/client/ClientBindAtoms.ts` | Matrix → atom bindings |
+
+## Data model
+
+Most state is **local only** (not Matrix). Exceptions: settings that also write account data (notification prefs via separate hooks).
+
+| Atom area | Persists? |
+|-----------|-----------|
+| settings | localStorage |
+| room list order | localStorage |
+| drafts | localStorage |
+| unread | memory (derived from sync) |
+| modals | memory |
+
+## Dependencies
+
+- `jotai`
+- `@tanstack/react-query` (separate from Jotai, used in App.tsx)
+
+## Integration points
+
+- **matrix-client**: sync updates room/unread atoms via ClientBindAtoms
+- **home-and-sidebar**: room list atoms
+- **room-timeline**: draft atoms
+- **routing-and-navigation**: navToActivePath
+
+## Testing
+
+### Manual
+
+1. Type draft, reload — draft should restore.
+2. Collapse category, reload — stays collapsed.
+3. Reorder rooms; verify order persists.
+4. Logout — verify which atoms clear vs persist.
+
+### Automated
+
+- None
+
+## Known issues & gotchas
+
+- Logout clears **all** localStorage in session-logout handler — wipes settings too
+- Atom families (`roomIdToMsgDraftAtomFamily`) — memory growth in many rooms
+- `ClientBindAtoms` must mount early or UI shows stale unreads
+
+## Future work
+
+- Selective localStorage clear on logout (keep non-sensitive prefs)
+- Document atom dependency graph
+
+## Related docs
+
+- [matrix-client HANDOFF](../matrix-client/HANDOFF.md)
+- [home-and-sidebar HANDOFF](../home-and-sidebar/HANDOFF.md)
+
+## Add your extra things here
+
+- `useSetting` hook in `state/hooks/settings.ts` — primary settings accessor
+- `joiningProgress.ts` — room join UX state