## What changed
- Add a `Ctrl+A` action and footer hint for archiving the selected session in the resume picker.
- Send archive requests through the app server, remove successfully archived sessions from the picker, and surface failures inline.
- Prevent duplicate actions while an archive is pending, preserve configured keybindings, and direct users to `/archive` when they select the current session.
- Ignore archive notifications for untracked side threads so they do not appear in agent navigation.
## Testing
- Cover successful, repeated, rejected, and failed archive requests, shortcut conflicts, footer rendering, and untracked-thread notifications.
GitOrigin-RevId: 20ea21c804a9685e46484d67df967859f9be4651