oduffy-delphi/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 coordinator: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)

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:

<!-- Review: Patrik — removed stale attribution artifact -->

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

# Sync-main invariant: ensure local main == origin/main before branching.
~/.claude/plugins/coordinator-claude/coordinator/bin/sync-main.sh
# If sync-main.sh exits non-zero, stop — do not create a worktree from stale main.

# Determine full path
path="$LOCATION/$BRANCH_NAME"

# Create worktree with new branch off the now-current main
git worktree add "$path" -b "$BRANCH_NAME" main
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 |

Stale-Snapshot Hazard

Parallel worktrees each see only the parent commit at the moment of branching — they do not receive subsequent commits made to the parent branch while they are in flight.

The hazard: If chunk A's worktree merges its changes to main while chunk B's worktree is still running, chunk B has no visibility into A's landed changes. When B returns, applying its diff blindly will overwrite or conflict with A's work — even on lines where both made changes that "shouldn't" conflict.

Two valid resolutions:

1. Sequence dependent chunks — don't parallelize them. If chunk B depends on or overlaps with chunk A's output, run B after A has landed and merged. Parallelism is only safe for truly disjoint file sets.

2. Superset + dedupe on return. When chunks have unavoidable overlap (discovered after the fact), take the superset of both changes and deduplicate — never blindly apply chunk B's diff over chunk A's landed change. The later chunk's version is not automatically correct; review the overlap and keep the right content from each.

Prefer option 1 at design time. Detecting overlap after both chunks are in flight and attempting superset reconciliation is significantly more expensive than sequencing correctly upfront.

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 coordinator:using-git-worktrees skill to set up an isolated workspace.

[Check .worktrees/ - exists]
[Verify ignored - git check-ignore confirms .worktrees/ is ignored]
[Create worktree: git worktree add .worktrees/auth -b feature/auth]
[Run npm install]
[Run npm test - 47 passing]

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

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:

<!-- Review: Patrik — removed ghost callers; brainstorming doesn't invoke this skill; subagent-driven-development no longer exists -->

• /execute-plan — Use when branch-level isolation is needed (not required for single-branch sequential execution)
• Any skill needing isolated workspace

Pairs with:

• finishing-a-development-branch - REQUIRED for cleanup after work complete