cmux and Worktrees

Run concurrent coding sessions safely by isolating each task in a git worktree.

Non-Negotiable Command Rule

• Use cmux for every command in this skill.
• Do not substitute git worktree in normal operation.
• If a cmux command fails, verify availability with type cmux first.

Preflight

1. Verify current directory is inside a git repo:

git rev-parse --is-inside-work-tree

1. Verify cmux is available:

type cmux

1. Ensure worktrees are ignored in git:

rg -n '^\.worktrees/$' .gitignore || echo '.worktrees/' >> .gitignore

1. Inspect active worktrees:

cmux ls

Core Commands

• Create new isolated task: cmux new <branch>
• Resume existing task: cmux start <branch>
• Jump to worktree: cmux cd [branch]
• List worktrees: cmux ls
• Merge into primary checkout: cmux merge [branch] [--squash]
• Remove worktree + branch: cmux rm [branch | --all] [--force]
• Generate setup hook: cmux init [--replace]
• Show/set layout config: cmux config, cmux config set layout <nested|outer-nested|sibling> [--global]
• Update tool: cmux update
• Show version: cmux version

Exact Workflows

Existing Branch -> Worktree

cd /path/to/repo
cmux ls
cmux start <existing-branch>
cmux cd <existing-branch>
bash .cmux/setup

Example:

cmux start eng-1296-onboarding-v2-question-view-context-dedupe
cmux cd eng-1296-onboarding-v2-question-view-context-dedupe
bash .cmux/setup

New Branch + New Worktree

cd /path/to/repo
cmux new <new-branch>
cmux cd <new-branch>
bash .cmux/setup

Example:

cmux new codex/pr1-onboarding-demographics-profile-report
cmux cd codex/pr1-onboarding-demographics-profile-report
bash .cmux/setup

Setup Hook Workflow

1. Generate a project-specific setup hook:

cmux init

1. If needed, regenerate:

cmux init --replace

1. Commit .cmux/setup so future worktrees inherit setup automatically.
2. Run setup after every cmux new and cmux start:

bash .cmux/setup

Branch and Path Behavior

• Treat new as "new branch + new worktree".
• Treat start as "reuse existing worktree/session".
• Expect worktree paths under .worktrees/<branch>/ in nested layout.
• Expect branch sanitization (e.g., feature/foo becomes feature-foo path name).
• One branch can only be checked out in one worktree at a time.

Safety Rules

• Ask for confirmation before cmux rm --all.
• Ask for confirmation before cmux rm --force.
• Prefer cmux merge <branch> --squash for compact history unless user requests full merge commits.
• Ensure worktree changes are committed before merging.
• Remove finished worktrees after successful merge to reduce branch/worktree drift.

Troubleshooting

• Not in a git repo: move to repo root, then rerun.
• Worktree not found: run cmux ls, then choose correct branch or create with cmux new <branch>.
• Branch already checked out: run cmux ls and use the existing worktree path.
• Merge blocked by uncommitted changes: commit or stash inside the worktree, then retry.
• Remove blocked by dirty tree: clean state first, or use cmux rm --force only with explicit confirmation.
• Expo Router shows "Welcome to Expo" unexpectedly: kill stale expo/metro processes, restart from the target worktree with --clear, and reopen dev client.
• Mobile dev from a worktree:

cd apps/mobile
npm run dev -- --clear --host lan