using-git-worktrees

name	using-git-worktrees
description	Use when starting feature work that needs isolation from current workspace or before executing implementation plans - creates isolated git worktrees with smart directory selection and safety verification

Using Git Worktrees

Overview

Git worktrees create isolated workspaces sharing the same repository, allowing work on multiple branches simultaneously without switching.

Core principle: Systematic directory selection + safety verification = reliable isolation.

Announce at start: "I'm using the using-git-worktrees skill to set up an isolated workspace."

In a mothership workspace

If a mothership.yaml is present at any ancestor directory, use mship spawn instead of the steps below — but every task needs a WorkItem first: mship item new "<title>" --kind <feature|bug|chore|question> (prints an id), then mship spawn '<description>' --work-item <id>. spawn refuses without --work-item (--hotfix overrides, logged). mship spawn creates the worktree, registers it in workspace state, runs per-repo task setup, and (where configured) symlinks heavy directories. The Directory Selection, Safety Verification, and Creation Steps sections below apply only when you're not spawning a mship task (e.g., quick read-only exploration or a non-mship repo).

Directory Selection Process

Follow this priority order:

1. Check Existing Directories

# Check in priority order
ls -d .worktrees 2>/dev/null     # Preferred (hidden)
ls -d worktrees 2>/dev/null      # Alternative

If found: Use that directory. If both exist, .worktrees wins.

2. Check CLAUDE.md

grep -i "worktree.*director" CLAUDE.md 2>/dev/null

If preference specified: Use it without asking.

3. Ask User

If no directory exists and no CLAUDE.md preference:

No worktree directory found. Where should I create worktrees?

1. .worktrees/ (project-local, hidden) [default]
2. worktrees/ (project-local, visible)

Which would you prefer?

Safety Verification

For Project-Local Directories (.worktrees or worktrees)

MUST verify directory is ignored before creating worktree:

# Check if directory is ignored (respects local, global, and system gitignore)
git check-ignore -q .worktrees 2>/dev/null || git check-ignore -q worktrees 2>/dev/null

If NOT ignored:

Per Jesse's rule "Fix broken things immediately":

1. Add appropriate line to .gitignore
2. Commit the change
3. Proceed with worktree creation

Why critical: Prevents accidentally committing worktree contents to repository.

Creation Steps

1. Detect Project Name

project=$(basename "$(git rev-parse --show-toplevel)")

2. Create Worktree

For non-mship workflows, create the worktree directly:

# Determine full path (default: .worktrees/)
LOCATION="${LOCATION:-.worktrees}"
path="$LOCATION/$BRANCH_NAME"

# Create worktree with new branch
git worktree add "$path" -b "$BRANCH_NAME"
cd "$path"

3. Run Project Setup

Auto-detect and run appropriate setup:

# Node.js
if [ -f package.json ]; then npm install; fi

# Rust
if [ -f Cargo.toml ]; then cargo build; fi

# Python
if [ -f requirements.txt ]; then pip install -r requirements.txt; fi
if [ -f pyproject.toml ]; then poetry install; fi

# Go
if [ -f go.mod ]; then go mod download; fi

4. Verify Clean Baseline

Run tests to ensure worktree starts clean:

# Examples - use project-appropriate command
npm test
cargo test
pytest
go test ./...

If tests fail: Report failures, ask whether to proceed or investigate.

If tests pass: Report ready.

5. Report Location

Worktree ready at <full-path>
Tests passing (<N> tests, 0 failures)
Ready to implement <feature-name>

Quick Reference

Situation	Action
.worktrees/ exists	Use it (verify ignored)
worktrees/ exists	Use it (verify ignored)
Both exist	Use .worktrees/
Neither exists	Check CLAUDE.md → Ask user
Directory not ignored	Add to .gitignore + commit
Tests fail during baseline	Report failures + ask
No package.json/Cargo.toml	Skip dependency install

Common Mistakes

Skipping ignore verification

• Problem: Worktree contents get tracked, pollute git status
• Fix: Always use git check-ignore before creating project-local worktree

Assuming directory location

• Problem: Creates inconsistency, violates project conventions
• Fix: Follow priority: existing > CLAUDE.md > ask

Proceeding with failing tests

• Problem: Can't distinguish new bugs from pre-existing issues
• Fix: Report failures, get explicit permission to proceed

Hardcoding setup commands

• Problem: Breaks on projects using different tools
• Fix: Auto-detect from project files (package.json, etc.)

Example Workflow

You: I'm using the using-git-worktrees skill to set up an isolated workspace.

[Detect: mothership.yaml found at /abs/workspace — routing through mship spawn]
[Run: mship item new "auth middleware" --kind feature]   # → wi-20260703-a1b2c3
[Run: mship spawn "implement auth middleware" --work-item wi-20260703-a1b2c3 --repos auth-service]
[mship creates worktree at .worktrees/implement-auth-middleware/auth-service, runs task setup]
[Run: mship test (baseline check)]

Worktree ready at /abs/workspace/.worktrees/implement-auth-middleware/auth-service
Tests passing (47 tests, 0 failures)
Ready to implement auth middleware

Red Flags

Never:

• Create worktree without verifying it's ignored (project-local)
• Skip baseline test verification
• Proceed with failing tests without asking
• Assume directory location when ambiguous
• Skip CLAUDE.md check

Always:

• Follow directory priority: existing > CLAUDE.md > ask
• Verify directory is ignored for project-local
• Auto-detect and run project setup
• Verify clean test baseline

Integration

Called by:

• brainstorming (Phase 4) - REQUIRED when design is approved and implementation follows
• subagent-driven-development - REQUIRED before executing any tasks
• executing-plans - REQUIRED before executing any tasks
• Any skill needing isolated workspace

Pairs with:

• finishing-a-development-branch - REQUIRED for cleanup after work complete (uses mship close in mothership workspaces; manual git worktree remove otherwise)