sartoris-digital/using-git-worktrees

Using Git Worktrees

Overview

Ensure work happens in an isolated workspace. Prefer the platform's native worktree tools when present. 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 whether the agent is already inside 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 the agent is not in a submodule:

# If this returns a path, the agent is 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): The agent is already in a linked worktree. Skip to Step 3 (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): The agent is in a normal repo checkout.

Has the user already indicated a worktree preference in the session 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 3.

Why consent matters: Earlier versions of the skill (and orchestration skills that called it) created worktrees implicitly. Surprise worktrees confuse users and pollute repositories. Always ask, or honor a declared preference.

Step 1: Create Isolated Workspace

Two mechanisms. Try them in this order.

1a. Native Worktree Tools (preferred)

The user has consented to an isolated workspace (Step 0). Does the harness expose a native worktree tool — something like EnterWorktree, WorktreeCreate, a /worktree command, or a --worktree flag? If so, use it and skip to Step 3.

Native tools handle directory placement, branch creation, and cleanup automatically. Using git worktree add when a native tool exists creates phantom state the harness cannot see or manage.

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

1b. Git Worktree Fallback

Only use this if Step 1a does not apply — there is no native worktree tool. Create a worktree manually using git worktree via bash.

Directory Selection

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

1. Check session 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. Check for an existing global directory:

   project=$(basename "$(git rev-parse --show-toplevel)")
   ls -d ~/.config/superpowers/worktrees/$project 2>/dev/null
   

   If found, use it (backward compatibility with legacy global path).

4. 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 the repository.

Global directories (~/.config/superpowers/worktrees/) need no verification.

Create the Worktree

project=$(basename "$(git rev-parse --show-toplevel)")

# Determine path based on chosen location
# For project-local: path="$LOCATION/$BRANCH_NAME"
# For global: path="~/.config/superpowers/worktrees/$project/$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 the agent is working in the current directory instead. Then run setup and baseline tests in place.

Step 3: 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 4: Verify Clean Baseline

Run tests to ensure the 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 via bash (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/ | | Global path exists | Use it (backward compat) | | 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 consent

• Problem: Worktrees appear without the user expecting them; orchestration skills auto-create silently
• Fix: Step 0 requires consent (or a pre-declared preference) before creation

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 > global legacy > instruction file > default

Proceeding with failing tests

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

Example Workflow

Agent: I'm using the using-git-worktrees skill to set up an isolated workspace.

[Step 0: GIT_DIR == GIT_COMMON, not a submodule — normal repo]
[No declared preference — ask for consent]
[User: yes]
[Step 1a: no native worktree tool on Pi — fall through]
[Step 1b: .worktrees/ exists, git check-ignore confirms ignored]
[Create worktree: git worktree add .worktrees/auth -b feature/auth]
[Run npm install]
[Run npm test - 47 passing]

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

Red Flags

Never:

• Create a worktree when Step 0 detects existing isolation
• Create a worktree without user consent (or pre-declared preference)
• Use git worktree add when a native worktree tool exists. This is the #1 mistake — if it exists, 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
• Get consent (or honor declared preference) before creation
• Prefer native tools over git fallback
• Follow directory priority: existing > global legacy > instruction file > default
• Verify directory is ignored for project-local
• Auto-detect and run project setup
• Verify clean test baseline

Pi Platform Notes

Pi has no native worktree tool. The bundled @mariozechner/pi-coding-agent tool registry and the pi-superpowers extension surface (bootstrap, subagent, state-manager, persistence-engine, orchestrator) do not expose any worktree, EnterWorktree, or ExitWorktree primitive. Step 1a will therefore never match on Pi — the skill always falls through to Step 1b and uses git worktree via bash.

Concrete Pi flow:

1. Step 0 detection runs with plain bash (git rev-parse --git-dir, --git-common-dir).
2. Step 1a probes for a native tool; on Pi this probe always returns nothing.
3. Step 1b runs git worktree add through bash.
4. Cleanup at finish time is delegated to finishing-a-development-branch, which removes the worktree with git worktree remove via bash (no rm -rf fallback — see that skill for the provenance rules).

If a future Pi extension registers a worktree tool, Step 1a will pick it up automatically and Step 1b becomes unreachable — no skill change required.

All other guidance (consent, safety checks, baseline tests, directory selection) applies unchanged.