## Why
Starting a side chat waits for fork and setup requests. Keep the workspace responsive during those requests and let users return to an existing side chat through the sidebar chooser.
## What changed
- Add a clickable `Side chat` tab and `+` chooser, plus the configurable `focus_sidebar_tabs` action bound to `leader t` by default.
- Create workspace side chats in the background, showing loading and failure states with `Enter` to retry and `Esc` to go back. Preserve opening prompts and avoid taking focus when the user has moved away.
- Retain inherited permission profiles and defer startup notifications until the side chat is registered on its owning backend.
- Quiet the parent composer while the chooser has focus and prevent completion popups or repeated activation keys from consuming chooser input.
## Testing
Extend tests and snapshots for loading and failure states, returning to an existing chat, draft preservation, inherited permissions, focus transitions, and deferred MCP startup notifications.
GitOrigin-RevId: 244bcd3f170819e2260f21dc1041cf8899fe048c
Felipe Coury
9df200a068