Using Git Worktrees

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."

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)
2. ~/.config/worktrees/<project-name>/ (global location)

Which would you prefer?

4. Agent-Created Worktrees

When agents (subagents, general-purpose agents, automated workflows) create worktrees, they MUST use the canonical location:

$ONEX_STATE_DIR/worktrees/{repo}/{branch}

This location:

• Is outside any project repo (no .gitignore needed)
• Has deterministic cleanup via SessionEnd hook
• Is scoped per-repo and per-branch for isolation

Do NOT use project-local directories for agent worktrees. Project-local .worktrees/ is for human-driven workflows only.

Safety Verification

For Project-Local Directories (.worktrees or worktrees)

MUST verify .gitignore before creating worktree:

# Check if directory pattern in .gitignore
grep -q "^\.worktrees/$" .gitignore || grep -q "^worktrees/$" .gitignore

If NOT in .gitignore:

Per best practices "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.

For Global Directory (~/.config/worktrees)

No .gitignore verification needed - outside project entirely.

Creation Steps

1. Detect Project Name

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

2. Create Worktree

# Determine full path
case $LOCATION in
  .worktrees|worktrees)
    path="$LOCATION/$BRANCH_NAME"
    ;;
  ~/.config/worktrees/*)
    path="~/.config/worktrees/$project/$BRANCH_NAME"
    ;;
esac

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

3. Post-Creation: Install pre-commit (REQUIRED)

After every worktree creation, install pre-commit hooks before writing any code:

cd ${ONEX_WORKTREES_ROOT:-~/omni_worktrees}/$TICKET/$REPO
pre-commit install --install-hooks

This is mandatory — pre-commit hooks enforce hardcoded-topic lint, import ordering, and other checks that run on every commit. Without this step, hooks never execute. If pre-commit is not in the venv: uv add pre-commit --dev or pip install pre-commit.

4. 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

5. 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.

6. Report Location

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

Session Marker

When creating a worktree at $ONEX_STATE_DIR/worktrees/, write a .claude-session.json marker file in the worktree root immediately after creation:

# After git worktree add
# NOTE: Run this from the parent repo directory, NOT from within the new worktree.
# git rev-parse --show-toplevel returns the worktree root if run inside one,
# which would set parent_repo_path incorrectly and break SessionEnd cleanup.
cat > "${worktree_path}/.claude-session.json" <<MARKER
{
  "session_id": "${SESSION_ID}",
  "created_at": "$(date -u +%Y-%m-%dT%H:%M:%SZ)",
  "repo": "${project}",
  "branch": "${BRANCH_NAME}",
  "worktree_path": "${worktree_path}",
  "parent_repo_path": "$(git rev-parse --show-toplevel)",
  "creator": "using-git-worktrees/1.0.0",
  "cleanup_policy": "session-end"
}
MARKER

Marker Fields

Without this marker, the worktree will NOT be cleaned up automatically.

Lifecycle Management

Automatic Cleanup (SessionEnd)

When a Claude Code session ends, the SessionEnd hook scans $ONEX_STATE_DIR/worktrees/ for worktrees with .claude-session.json markers matching the current session ID.

A worktree is removed if ALL conditions are met:

1. Has a valid .claude-session.json marker with cleanup_policy: "session-end"
2. Marker session_id matches the ending session
3. parent_repo_path from marker exists and is a valid directory
4. No uncommitted changes (git diff --quiet)
5. No staged changes (git diff --cached --quiet)
6. No unpushed commits (upstream configured, remote ref resolvable, local HEAD matches upstream)
7. Path is under $ONEX_STATE_DIR/worktrees/ (traversal guard)

If ANY condition fails, the worktree is logged as STALE but NOT deleted.

What Gets Cleaned Up

Manual Cleanup

For stale worktrees that weren't auto-cleaned:

# List all worktrees under $ONEX_STATE_DIR/worktrees
find $ONEX_STATE_DIR/worktrees -name '.claude-session.json' -exec jq -r '.repo + "/" + .branch + " (session: " + .session_id + ")"' {} \;

# Remove a specific stale worktree (from parent repo)
cd /path/to/parent/repo
git worktree remove $ONEX_STATE_DIR/worktrees/repo/branch
git worktree prune

Quick Reference

Common Mistakes

Skipping .gitignore verification

• Problem: Worktree contents get tracked, pollute git status
• Fix: Always grep .gitignore 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.

[Check .worktrees/ - exists]
[Verify .gitignore - contains .worktrees/]
[Create worktree: git worktree add .worktrees/auth -b feature/auth]
[Run npm install]
[Run npm test - 47 passing]

Worktree ready at <home>/myproject/.worktrees/auth
Tests passing (47 tests, 0 failures)
Ready to implement auth feature

Red Flags

Never:

• Create worktree without .gitignore verification (project-local)
• Skip baseline test verification
• Proceed with failing tests without asking
• Assume directory location when ambiguous
• Skip CLAUDE.md check
• Use rm -rf to clean up worktrees (use git worktree remove instead)
• Create agent worktrees without .claude-session.json marker

Always:

• Follow directory priority: existing > CLAUDE.md > ask
• Verify .gitignore for project-local
• Auto-detect and run project setup
• Verify clean test baseline
• Write .claude-session.json when creating agent worktrees
• Use git worktree remove + git worktree prune for cleanup

Integration

Called by:

• design-to-plan (Phase 4) - REQUIRED when design is approved and implementation follows
• Any skill needing isolated workspace

Pairs with:

• finishing-a-development-branch - REQUIRED for cleanup after work complete
• executing-plans or multi-agent --mode sequential-with-review - Work happens in this worktree