v0.77.0: GPT-5.4 Mini model, faster @ search indexing, and sub-agent improvements

New features

- GPT-5.4 Mini model - New GPT-5.4 Mini model available in the model selector

Improvements

- Faster @ search indexing - File indexing for @ mentions now runs in a background worker for improved responsiveness
- Faster session listing - The /sessions command is now optimized with an index for quicker loading
- Faster first prompt - System info is now prefetched before the first prompt for quicker startup
- Sub-agent reliability - Redesigned sub-agent architecture for improved task delegation reliability
- Skills preserved after compaction - Skills invoked during a session are now preserved when context is compacted
- Droid Computer selection UI - Improved visual design for the Droid Computer selection interface (Factory App)

Bug fixes

- Slash command arguments - Fixed slash command arguments being lost when submitting via the suggestion menu
- Missions model selection - Missions now correctly uses the session model instead of the global settings model
- Worktree error messages - Worktree setup failures now show descriptive error messages instead of generic errors
- Stale Missions warnings - Fixed stale Missions runs incorrectly triggering concurrent run warnings
- Mode preservation on /new - Fixed session mode being reset when creating a new session with /new
- Permission settings persistence - Permission settings are now preserved across session respawns
- Chat composer undo - Fixed undo not working after pasting text in the chat composer (Factory App)