Support cmux as a terminal backend for agent teams

Feature Request

Add cmux as a supported terminal backend for Claude Code agent teams, alongside the existing tmux and iTerm2 backends.

Background

cmux is a native macOS terminal application built on Ghostty's rendering engine, designed specifically for AI coding agent workflows. It provides vertical tabs with git branch/working directory context, notification rings for process alerts, split panes, and an embedded browser — all GPU-accelerated via libghostty.

Crucially, cmux exposes a CLI and socket API for automation and scripting, and already documents integration with Claude Code hooks for notifications. This makes it a strong candidate for agent team pane management.

Current Behavior

Claude Code agent teams currently support three teammateMode options:

• tmux — spawns teammates in tmux split panes
• iTerm2 — uses the it2 CLI
• in-process — fallback with no visible panes

There is no way to configure cmux as a backend. Users running cmux must either fall back to in-process mode (losing pane visibility) or nest tmux inside cmux.

Proposed Behavior

Add cmux as a teammateMode option that:

1. Detects cmux availability (e.g., via its CLI or socket)
2. Creates split panes for each teammate using the cmux socket/CLI API
3. Routes teammate I/O through cmux panes
4. Supports the same lifecycle operations (create, monitor, shutdown) as the tmux backend

Why This Matters

cmux is purpose-built for multi-agent terminal workflows — exactly the use case Claude Code teams target. Its visual features (notification rings, git context in tabs, embedded browser) provide a better UX for monitoring agent teams than raw tmux panes. As AI-native terminals gain adoption, supporting them alongside traditional multiplexers would keep Claude Code's team experience best-in-class.

References

• cmux website: https://www.cmux.dev/
• cmux GitHub: https://github.com/manaflow-ai/cmux
• cmux socket API docs: https://www.cmux.dev/docs/api