Using Git Worktrees

Overview

Isolation costs a setup step and a second checkout, so it earns its place. Create one when:

• Concurrency — another agent, process or session writes to the same repo.
• The user asked for an isolated or separate workspace.
• Interference — the work would disturb the current checkout: a long experiment, a migration with generated files, or a change that must stay buildable while main keeps moving.

Otherwise a bounded single-writer change belongs in the checkout you already have. Don't manufacture a workspace decision before implementation, and don't ask the user to choose between isolation mechanisms you can already resolve.

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)

Verify the directory is ignored before creating the worktree:

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

If NOT ignored: add the path to the repository's local exclude file — it is private to this clone and never reaches the user's tracked files:

printf '.worktrees/\n' >> "$(git rev-parse --git-common-dir)/info/exclude"

Edit .gitignore only when the ignore rule genuinely belongs to the project (other people checking out this repo would create the same directory). Recheck that exact path afterwards. Neither operation authorizes a commit.

Why: an unignored worktree directory lets git add . sweep the whole tree into a commit.

Create the Worktree

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

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

To attach to an existing branch (a merge location, for example), omit -b: git worktree add "$path" "<branch>". Git refuses a branch already checked out in another worktree; git worktree add --detach "$path" "<branch>" gives a detached checkout of its commit for verification without moving the branch.

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.

Removing a Worktree

Removal can destroy uncommitted files and strand commits. Remove only a workspace this task created, and only when the authorized integration includes its cleanup.

• Ownership comes from provenance. This task created the workspace (Step 1a or 1b) and recorded its path and branch. A .worktrees/ name, a stale-looking path or a matching branch name does not prove ownership. Host- or user-created workspaces, and detached externally managed ones, are host-owned: leave them in place, and use the platform's workspace-exit tool if it has one.

• Inventory what would be lost. Inside the workspace, capture WT_PATH=$(git rev-parse --show-toplevel), then identify the exact files and commits:

  git -C "$WT_PATH" status --porcelain -uall --ignored   # modified, untracked and ignored files
  git -C "$WT_PATH" log --oneline "<base-branch>..HEAD"  # commits not in base

  Ignored files (build output, a local .env) are deleted without warning, so decide them explicitly.

• Remove from outside the workspace. cd to the main checkout root (MAIN_ROOT, as in git-workflow step 4) first, using the path captured before any directory change. Removing the directory you are standing in fails on Windows with Permission denied; elsewhere it leaves the shell in a deleted directory.

• Remove without --force:

  git worktree remove "$WT_PATH"
  git worktree prune

  Git refuses when the worktree has modified tracked files or untracked files. Ignored files do not block removal.

• If removal is refused, show the unique files and ask which: commit them to the branch (needs commit authority), move them into the main repo root, or delete them (unrecoverable; needs explicit authority naming those files). Carry out the choice, then retry the plain removal. Never add --force on your own initiative.
• Branch. git branch -d <branch> after a merge; git refuses unmerged branches. git branch -D only under explicit discard authority naming the commits being discarded.

Quick Reference

Common Rationalizations

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