- Create attachment type system with file, text, symbol, and agent sources
- Implement file picker with SDK integration (find.files, file.status)
- Add @ detection in prompt input to trigger file search
- Create attachment chips UI for managing attached files
- Add attachment state management per session
- Update message submission to include attachments
- Implement drag & drop support for adding files
- Show git-modified files first in file picker with +/- indicators
- Filter files as user types after @
- Clear attachments after successful message send
