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/custom-emoji-packs/HANDOFF.md

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+# Custom emoji packs — handoff
+
+## Summary
+
+Built-in (non-plugin) custom emoji system: read image packs from room state, resolve shortcodes to images in messages and autocomplete. Distinct from user-installed JS plugins but shares pack format concepts.
+
+## User-facing behavior
+
+- Room/space emoji packs in settings
+- `:shortcode:` in composer resolves to pack image
+- Pack viewer for browsing stickers/emojis
+- Integrates with `im.ponies.room_emotes` and pack MXC structure
+
+## Architecture
+
+```
+plugins/custom-emoji/
+  PackMetaReader, PackImageReader, PackImagesReader
+  ImagePack.ts, PackAddress.ts
+emoji plugin (plugins/emoji.ts) — render shortcodes
+settings emojis-stickers + common-settings emojis
+```
+
+## Key files
+
+| Path | Role |
+|------|------|
+| `cinny/src/app/plugins/custom-emoji/PackMetaReader.ts` | Read pack metadata |
+| `cinny/src/app/plugins/custom-emoji/PackImageReader.ts` | Single image |
+| `cinny/src/app/plugins/custom-emoji/PackImagesReader.ts` | Bulk images |
+| `cinny/src/app/plugins/custom-emoji/ImagePack.ts` | Pack model |
+| `cinny/src/app/plugins/custom-emoji/types.ts` | Types |
+| `cinny/src/app/plugins/emoji.ts` | Shortcode rendering |
+| `cinny/src/app/plugins/recent-emoji.ts` | Recent emoji helper |
+| `cinny/src/app/components/image-pack-view/ImagePackView.tsx` | Pack browser UI |
+| `cinny/src/app/hooks/useImagePackRooms.ts` | Rooms with packs |
+
+## Data model
+
+| Event | Purpose |
+|-------|---------|
+| `im.ponies.room_emotes` | Room emoji pack definition |
+| Image pack account data | User/global packs (see emoji-stickers) |
+
+## Dependencies
+
+- MXC media URLs
+- `useMediaAuthentication` for protected media
+
+## Integration points
+
+- **emoji-stickers**: settings UI for packs + Telegram import
+- **message-rendering**: emoji.ts in parse pipeline
+- **editor-and-composer**: EmoticonAutocomplete
+
+## Testing
+
+### Manual
+
+1. Add emoji pack to room.
+2. Type `:shortcode:` in composer; image inserts.
+3. View pack in ImagePackView.
+4. Encrypted room pack visibility.
+
+### Automated
+
+- None
+
+## Known issues & gotchas
+
+- Pack address parsing in `PackAddress.ts` — MXC format sensitive
+- Large packs slow autocomplete — consider lazy load
+- Telegram import creates separate pack ids (`telegram_*`)
+
+## Future work
+
+- Pack CDN cache
+- Animated emoji support audit
+
+## Related docs
+
+- [emoji-stickers HANDOFF](../emoji-stickers/HANDOFF.md)
+- [message-rendering HANDOFF](../message-rendering/HANDOFF.md)
+
+## Add your extra things here
+
+- `StateEvent.PoniesRoomEmotes = 'im.ponies.room_emotes'` in room.ts