Add kitty terminal emulator backend

[DmitryAkDev]

Add kitty terminal emulator backend

Add support for kitty as a subagent surface backend, enabling spawning and management of sub-agents in separate kitty windows or tabs via the kitten @ remote control API.

What's Included

kitty Backend (cmux.ts)

• Runtime detection — isKittyRuntimeAvailable() checks KITTY_PID + KITTY_WINDOW_ID + remote control via KITTY_LISTEN_ON socket (works from TUI context where /dev/tty is unavailable)
• Two surface modes:
  • window (default) — split window inside current tab, auto-balanced side-by-side via horizontal layout
  • tab — new dedicated tab with full terminal space
• Full lifecycle — create, send commands, send escape, read screen, close surface, rename tab
• Auto-rebalance — after create/close, switches to horizontal layout for equal-width side-by-side windows

Configuration (index.ts)

• Agent frontmatter — kitty-mode: tab or kitty-mode: window in agent .md YAML frontmatter
• Resolution — agent frontmatter → default ("window")
• Tool parameter not added (avoids breaking general API schema)

Documentation (README.md)

• kitty added to supported multiplexers list
• Setup instructions (kitty.conf requirements)
• Surface mode documentation with frontmatter and tool parameter examples

Requirements

Add to ~/.config/kitty/kitty.conf:

allow_remote_control socket-only
listen_on unix:/tmp/kitty-rc

Then start pi inside kitty: kitty pi

Or force via environment: PI_SUBAGENT_MUX=kitty

API Mapping

Operation	kitty Command
Create (window)	kitten @ launch --type=window --location vsplit --keep-focus
Create (tab)	kitten @ launch --type=tab --keep-focus
Send command	kitten @ send-text --match id:N
Send Escape	kitten @ action --match id:N send_key Escape
Read screen	kitten @ get-text --match id:N
Close	kitten @ close-window --match id:N
Rename	kitten @ set-window-title --match id:N
Rebalance	kitten @ goto-layout horizontal

Testing

Tested on kitty 0.46.2:

• Single subagent launch → completion → window close
• Multiple concurrent subagents (4+) with auto-rebalance
• Tab mode (separate tab, auto-close on completion)
• Window mode (split, horizontal layout, equal widths)
• Real tasks (file operations, code analysis) with correct summary extraction

Notes

• horizontal layout chosen over grid for side-by-side arrangement (grid creates 2×2 layout)
• splits layout remembers old sizes — not suitable for rebalance (switching to grid then back to splits restores original proportions)
• Socket-based remote control (KITTY_LISTEN_ON) used instead of /dev/tty DCS sequences for TUI compatibility