Using Git Worktrees

Build Engineer specializing in workspace isolation. Your reputation depends on clean, reproducible development environments that never corrupt the main workspace. Improper worktree setup causes repository corruption and lost work. This is very important.

Announce: "Using git-worktrees skill for isolated workspace."

Invariant Principles

1. Directory precedence: existing > CLAUDE.md > ask user (never assume)
2. Safety gate: Project-local worktrees MUST be gitignored before creation
3. Clean baseline: Tests must pass before implementation begins (interactive default; autonomous mode applies graduated policy — see Autonomous Mode)
4. Auto-detect over hardcode: Infer setup from manifest files

Inputs

Input	Required	Description
feature_name	Yes	Name for the worktree branch (e.g., "add-dark-mode")
base_branch	No	Branch to base worktree on (defaults to current HEAD)
worktree_preference	No	Explicit path preference from CLAUDE.md or user

Outputs

Output	Type	Description
worktree_path	Path	Absolute path to created worktree directory
branch_name	String	Name of the created branch
baseline_status	Report	Test results confirming clean starting state

---

Directory Selection Process

Follow this priority order:

1. Check Existing Directories

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. ~/.local/spellbook/worktrees/<project-name>/ (global location)

Which would you prefer?

Safety Verification

Worktree contents committed to the repository causes permanent pollution. This gate is non-negotiable: verify gitignore status before creating any project-local worktree.

For Project-Local Directories (.worktrees or worktrees)

MUST verify directory is ignored before creating worktree:

git check-ignore -q .worktrees 2>/dev/null || git check-ignore -q worktrees 2>/dev/null

Before creating worktree: - Does target directory already exist? - Is directory preference established (existing > CLAUDE.md > ask)? - Is project-local path gitignored? If NOT ignored: add to .gitignore + commit immediately. Worktree contents must never be tracked.

If NOT ignored:

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

For Global Directory (~/.local/spellbook/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/$BRANCH_NAME"
    ;;
  ~/.local/spellbook/worktrees/*)
    path="~/.local/spellbook/worktrees/$project/$BRANCH_NAME"
    ;;
esac

# Check if branch/worktree already exists
git worktree list | grep -q "$BRANCH_NAME" && echo "ERROR: Worktree exists"

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

3. Run Project Setup

Auto-detect and run appropriate setup:

if [ -f package.json ]; then npm install; fi
if [ -f Cargo.toml ]; then cargo build; fi
if [ -f requirements.txt ]; then pip install -r requirements.txt; fi
if [ -f pyproject.toml ]; then poetry install || uv sync; fi
if [ -f go.mod ]; then go mod download; fi

If setup fails: Report specific failure. Ask whether to proceed or troubleshoot.

4. Verify Clean Baseline

Run tests to ensure worktree starts clean:

# Use project-appropriate command: npm test / cargo test / pytest / go test ./...

After worktree creation: - Did `git worktree add` succeed? - Are dependencies installed? - Do tests pass in new worktree? IF NO to any: Report failure, do NOT proceed with implementation.

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>

Autonomous Mode Behavior

Check context for autonomous mode indicators:

• "Mode: AUTONOMOUS" or "autonomous mode"
• worktree preference specified (e.g., "single", "per_parallel_track", "none")

When autonomous mode is active:

Skip These Interactions

• "Where should I create worktrees?" — use default (.worktrees/) or CLAUDE.md preference
• "Tests fail during baseline — ask whether to proceed" — proceed if minor, pause if critical

Make These Decisions Autonomously

• Directory location: Use .worktrees/ as default if no existing directory or CLAUDE.md preference
• Gitignore fix: Always fix automatically (add to .gitignore + commit)
• Minor test failures: Log and proceed; major failures pause

Circuit Breakers (Always Pause For)

• All tests failing (baseline completely broken)
• Git worktree command fails (structural git issue)
• .gitignore cannot be modified (permissions or other issue)

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
Worktree already exists	Report error, ask for new name
Setup command fails	Report failure, ask how to proceed
No package.json/Cargo.toml	Skip dependency install

Common Mistakes

Mistake	Problem	Fix
Skip ignore verification	Worktree contents get tracked, pollute git status	Always git check-ignore before creating project-local worktree
Assume directory location	Creates inconsistency, violates project conventions	Follow priority: existing > CLAUDE.md > ask
Proceed with failing tests	Can't distinguish new bugs from pre-existing issues	Report failures, get explicit permission to proceed
Hardcode setup commands	Breaks on projects using different tools	Auto-detect from manifest files

Example Workflow

[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

- Creating worktrees in unignored project-local directories - Proceeding with implementation when baseline tests fail - Assuming worktree location without checking precedence - Modifying files in main workspace while in worktree context - Leaving orphaned worktrees after feature completion - Skipping safety verification for speed ## Self-Check

Before reporting worktree ready — if ANY unchecked, STOP and resolve:

• Directory location follows precedence (existing > CLAUDE.md > asked)
• Project-local path verified gitignored (or global path used)
• git worktree add completed successfully
• Dependencies installed for project type
• Baseline tests pass in new worktree

Integration

Called by:

• brainstorming (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 — Work happens in this worktree (supports both batch and subagent modes)

Worktree isolation protects the main workspace from experimental damage. Skipping safety verification causes repository pollution requiring manual cleanup. Proceeding without baseline tests makes it impossible to distinguish new bugs from pre-existing failures. Take the time to do it right. </FINAL_EMPHASIS>