cmuxLayer

Your AI agents can't see each other's terminals. One runs in tab 1, another in tab 2 — and you're the clipboard between them. cmuxLayer fixes that: 35 MCP tools that give AI agents programmatic control over terminal workspaces.

<p align="center"> <img src="./assets/cmuxlayer-logo-split-pane-grid.svg" alt="cmuxLayer" width="96" height="96" /> </p>

Quick Start

brew install etanhey/layers/cmuxlayer       # stable, pinned release
brew install --HEAD etanhey/layers/cmuxlayer # or: dogfood the latest main

This installs the cmuxlayer command (plus cmuxlayer-app-server / cmuxlayer-proxy). Requires cmux to be running. For how the golem fleet wires, versions, and dogfoods it — and the CMUX_SOCKET_PATH instance pin — see docs/releases-and-brew.md.

Optional fleet sidebar

The lane-grouped fleet view is opt-in. Install its fallback file with:

bun run install:fleet-sidebar

cmuxLayer then refreshes ~/.config/cmux/sidebars/fleet.swift from its reconciled live-agent snapshot. It does not change cmux settings or replace the stock sidebar. To activate it, right-click the sidebar toggle and choose fleet; choose the stock entry there whenever you want the fallback UI.

Development and screenshot QA use a separate picker entry and never publish to the live fleet.swift path:

bun run install:fleet-sidebar:dev
bun run dev

Those commands publish only ~/.config/cmux/sidebars/fleet-dev.swift; choose fleet-dev in cmux while testing. Runtime tests must inject a temporary publisher outputPath.

Add to your MCP config:

Codex CLI / T3 Code

T3 Code inherits MCP servers from the Codex CLI config file at ~/.codex/config.toml (or $CODEX_HOME/config.toml).

[mcp_servers.cmuxlayer]
command = "cmuxlayer"

Claude Code, Cursor, VS Code, Claude Desktop

{
  "mcpServers": {
    "cmuxlayer": {
      "command": "cmuxlayer"
    }
  }
}

To keep only a per-session resident subset of tools, set CMUXLAYER_DEFAULT_PALETTE to comma-separated bare tool names, for example list_surfaces,spawn_agent,send_to. The server also exposes expand_palette, which makes every deferred tool available for the rest of that MCP session. When unset or blank, the signed 12-tool thin-core default applies. When set, the environment value overrides that default for the session. Unknown names are warned and ignored while valid names still load.

Config locations: Codex CLI / T3 Code ~/.codex/config.toml (or $CODEX_HOME/config.toml) | Claude Code .mcp.json or claude mcp add cmuxlayer -s user -- cmuxlayer | Cursor .cursor/mcp.json | VS Code .vscode/mcp.json | Claude Desktop — see MCP docs for platform-specific paths

What You Can Do

Tell your AI agent things like:

• "Split a pane to the right and run my test suite there"
• "Spawn a Claude Code agent in a new pane to refactor auth.ts"
• "Read the screen of surface:2 and tell me if the build passed"
• "Wait for all agents to finish, then read their output"
• "Set the sidebar status to show our deploy progress"

Under the hood, cmuxLayer keeps 42 MCP tools callable for terminal control, screen reading, layout management, and multi-agent orchestration. The default palette is intentionally limited to 12; the remaining tools are loaded through ToolSearch. reorder_surface is the single approved deletion. read_screen parses agent metadata (status, model, tokens, context %