Using git worktrees

Using Git Worktrees

Overview

Ensure work happens in an isolated workspace. Prefer your platform's native worktree tools. Fall back to manual git worktrees only when no native tool is available.

Core principle: Detect existing isolation first. Then use native tools. Then fall back to git. Never fight the harness.

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

Step 0: Detect Existing Isolation

Before creating anything, check if you are already in an isolated workspace.

GIT_DIR=$(cd "$(git rev-parse --git-dir)" 2>/dev/null && pwd -P)
GIT_COMMON=$(cd "$(git rev-parse --git-common-dir)" 2>/dev/null && pwd -P)
BRANCH=$(git branch --show-current)

Submodule guard: GIT_DIR != GIT_COMMON is also true inside git submodules. Before concluding "already in a worktree," verify you are not in a submodule:

# If this returns a path, you're in a submodule, not a worktree — treat as normal repo
git rev-parse --show-superproject-working-tree 2>/dev/null

If GIT_DIR != GIT_COMMON (and not a submodule): You are already in a linked worktree. Skip to Step 2 (Project Setup). Do NOT create another worktree.

Report with branch state:

• On a branch: "Already in isolated workspace at <path> on branch <name>."
• Detached HEAD: "Already in isolated workspace at <path> (detached HEAD, externally managed). Branch creation needed at finish time."

If GIT_DIR == GIT_COMMON (or in a submodule): You are in a normal repo checkout.

Has the user already indicated their worktree preference in your instructions? If not, ask for consent before creating a worktree:

"Would you like me to set up an isolated worktree? It protects your current branch from changes."

Honor any existing declared preference without asking. If the user declines consent, work in place and skip to Step 2.

Step 0.5: GitHub Issue → Branch (entry points)

When the work is tracked by a GitHub issue, the branch is created from the issue so GitHub links the two (the branch shows under the issue's Development section). Two entry points feed this:

Entry A — started from chat (spec not yet an issue). You brainstormed in chat (superpowers-custom:brainstorming) and a spec landed. Write that spec to a new issue, then branch from it:

# Write the finalized spec to a file first (use the Write tool, not echo),
# then create the issue from it — never inline --body (shell metachars).
issue_url=$(gh issue create --title "<concise title>" --body-file <spec-file>)
issue_num=$(printf '%s' "$issue_url" | grep -oE '[0-9]+$')

Entry B — started from an existing issue. The user gives an issue link or number; read the spec from it:

issue_num=<number>            # from the link the user gave
gh issue view "$issue_num"    # read the spec that already lives in the issue

Both entry points then create the linked branch via the GH API and check it out (gh issue develop calls the createLinkedBranch GraphQL mutation under the hood, so the branch is associated with the issue):

branch="<type>/<issue_num>-<slug>"          # e.g. feat/123-token-refresh
gh issue develop "$issue_num" --name "$branch" --base main
# --name creates+links the branch WITHOUT checking out, so a worktree can
# attach to it next. (Omit Step 1's `-b`: the branch already exists.)

If you are NOT using a worktree, add --checkout to switch to the branch in place and skip to Step 2. Otherwise carry $branch into Step 1 and attach the worktree to the existing branch. The plan you write next (superpowers-custom:writing-plans) draws its requirements from the issue spec.

Step 1: Create Isolated Workspace

You have two mechanisms. Try them in this order.

1a. Native Worktree Tools (preferred)

The user has asked for an isolated workspace (Step 0 consent). Do you already have a way to create a worktree? It might be a tool with a name like EnterWorktree, WorktreeCreate, a /worktree command, or a --worktree flag. If you do, use it and skip to Step 2.

Native tools handle directory placement, branch creation, and cleanup automatically. Using git worktree add when you have a native tool creates phantom state your harness can't see or manage.

Only proceed to Step 1b if you have no native worktree tool available.

1b. Git Worktree Fallback

Only use this if Step 1a does not apply — you have no native worktree tool available. Create a worktree manually using git.

Directory Selection

Follow this priority order. Explicit user preference always beats observed filesystem state.

1. Check your instructions for a declared worktree directory preference. If the user has already specified one, use it without asking.

2. Check for an existing project-local worktree directory:

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

   If found, use it. If both exist, .worktrees wins.

3. If there is no other guidance available, default to .worktrees/ at the project root.

Safety Verification (project-local directories only)

MUST verify directory is ignored before creating worktree:

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

If NOT ignored: Add to .gitignore, commit the change, then proceed.

Why critical: Prevents accidentally committing worktree contents to repository.

Update the parent branch first (mandatory)

Before creating the worktree, fetch and fast-forward the parent branch you are basing off (usually main). A worktree created from a stale local parent starts the new branch behind the real tip; its eventual PR then silently reverts every commit that landed on the parent since your last pull, and CI rejects it as touching unrelated files.

git fetch origin
git checkout <parent>                 # usually main
git pull --ff-only origin <parent>

Create the Worktree

# Determine path based on chosen location
path="$LOCATION/$BRANCH_NAME"

# Base the new branch on the freshly-updated parent tip.
git worktree add "$path" -b "$BRANCH_NAME" origin/<parent>
cd "$path"

If the branch already exists (e.g. created from a GitHub issue in Step 0.5), attach to it instead of creating a new one — drop the -b:

git worktree add "$path" "$BRANCH_NAME"   # BRANCH_NAME = the issue's linked branch
cd "$path"

Sandbox fallback: If git worktree add fails with a permission error (sandbox denial), tell the user the sandbox blocked worktree creation and you're working in the current directory instead. Then run setup and baseline tests in place.

Step 2: 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

Step 3: Verify Clean Baseline

Run tests to ensure workspace starts clean:

# 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.

Report

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

Quick Reference

Situation	Action
Already in linked worktree	Skip creation (Step 0)
In a submodule	Treat as normal repo (Step 0 guard)
Native worktree tool available	Use it (Step 1a)
No native tool	Git worktree fallback (Step 1b)
.worktrees/ exists	Use it (verify ignored)
worktrees/ exists	Use it (verify ignored)
Both exist	Use .worktrees/
Neither exists	Check instruction file, then default .worktrees/
Directory not ignored	Add to .gitignore + commit
Permission error on create	Sandbox fallback, work in place
Tests fail during baseline	Report failures + ask
No package.json/Cargo.toml	Skip dependency install

Common Mistakes

Fighting the harness

• Problem: Using git worktree add when the platform already provides isolation
• Fix: Step 0 detects existing isolation. Step 1a defers to native tools.

Skipping detection

• Problem: Creating a nested worktree inside an existing one
• Fix: Always run Step 0 before creating anything

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: explicit instructions > existing project-local directory > default

Proceeding with failing tests

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

Red Flags

Never:

• Create a worktree when Step 0 detects existing isolation
• Use git worktree add when you have a native worktree tool (e.g., EnterWorktree). This is the #1 mistake — if you have it, use it.
• Skip Step 1a by jumping straight to Step 1b's git commands
• Create worktree without verifying it's ignored (project-local)
• Skip baseline test verification
• Proceed with failing tests without asking

Always:

• Run Step 0 detection first
• Prefer native tools over git fallback
• Follow directory priority: explicit instructions > existing project-local directory > default
• Verify directory is ignored for project-local
• Auto-detect and run project setup
• Verify clean test baseline