Using Git Worktrees

Using Git Worktrees

Overview

Use isolation when the task or concurrent writers require it. For a bounded local change in a usable checkout, work in place unless the user requested otherwise. Do not manufacture a workspace decision before implementation.

Core principle: Preserve existing work. Reuse existing isolation; prefer native tools when creating it, then fall back to git.

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: preserve the externally managed workspace; name a branch only if authorized integration requires one.

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

Honor the user's declared workspace preference. With no isolation need, work in place and continue to Step 2. If isolation is required, use the platform's existing task-isolation mechanism or a task-scoped worktree; ask only when an unresolved workspace choice would move, discard or interfere with user work.

Step 1: Create Isolated Workspace

You have two mechanisms. Try them in this order.

1a. Native Worktree Tools (preferred)

Isolation is needed or requested (Step 0). Use a native facility such as EnterWorktree, WorktreeCreate, /worktree or --worktree if available, then continue 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 the chosen directory to the local exclude file, or update .gitignore when shared ignore policy belongs to the task. Recheck that exact path. Neither operation authorizes a commit.

Why critical: Prevents accidentally committing worktree contents to repository.

Create the Worktree

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

git worktree add "$path" -b "$BRANCH_NAME"
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

Inspect the documented project setup and available environment. Reuse installed dependencies; install only missing requirements needed for this task, using the project's lockfile and package manager. A manifest's presence alone is not a reason to install, build or contact the network.

Step 3: Verify Clean Baseline

Run the relevant baseline check when no valid evidence exists for this state. Broaden only for shared impact, integration requirements or observed failures.

If checks fail: Preserve the checkout and identify the cause. Repair task-related failures within scope and continue reachable work. Report unrelated or environment failures separately; ask only for a concrete missing prerequisite or authority, not merely because a baseline is red.

If checks pass: Continue the authorized implementation immediately. Report workspace details only when they affect the user's work; do not stop at a "ready to implement" handoff.

Quick Reference

Common Rationalizations

Source: obra/superpowers (MIT). Adapted for coding-kit: cross-references made local.