andreaswasita/copilot-agents-dojo/using-git-worktrees

Using Git Worktrees Skill

Creates an isolated git worktree on a dedicated feature branch for every development task, so main is never touched until finishing-a-development-branch says so. Does NOT replace feature branches when worktrees are impractical (CI, single-file fix) — the isolation principle is what matters.

When to Use

• Starting any non-trivial development task (default behavior).
• Before the agent would otherwise modify code on main.
• When parallel development tracks are needed (multiple worktrees in flight).
• After brainstorming produces an approved design.
• NOT for a one-line typo fix where a branch is sufficient.

Prerequisites

• git ≥ 2.5 with worktree support.
• The repository is already cloned (a worktree extends an existing clone).
• The powershell Copilot tool to run git.
• A naming convention agreed for the branch: feature/*, fix/*, experiment/*.
• The project's dependency install command (npm install, pip install -r requirements.txt, etc.).

How to Run

1. From the main repo root, create the worktree with a new branch.
2. Change into the worktree directory.
3. Install dependencies inside it.
4. Confirm a green test baseline.
5. Work only inside the worktree — never touch the main worktree.

Quick Reference

Procedure

Step 1: Create the Worktree

From the main repo root, run via the powershell tool:

git worktree add ../project-feature-name -b feature/feature-name
cd ../project-feature-name

Use a directory name that is obviously not the main repo so you cannot edit the wrong one by accident.

Step 2: Install Dependencies

Detect the stack from the table above and run the matching install command. A worktree shares .git, not node_modules / .venv / build artifacts.

Step 3: Establish a Green Baseline

Run the project's test command via the powershell tool. Capture pass/fail counts before changing any code. If the baseline is red, fix it first or explicitly acknowledge the broken tests in tasks/todo.md.

git status --porcelain         # must be empty
git branch --show-current      # must be the new feature branch
<project test command>         # must exit 0 for a clean baseline

Step 4: Work Inside the Worktree

All commits go to the feature branch. The main repo's working tree is read-only for the duration. Open files and run commands only from inside the worktree directory.

Step 5: When Worktrees Are Impractical

For CI environments, single-file fixes, or systems without worktree support:

git checkout -b feature/<slug>

The isolation principle still applies: never commit to main.

Step 6: Cleanup (handled later)

Worktree teardown is owned by finishing-a-development-branch. Do not remove the worktree mid-task.

Pitfalls

• DO NOT commit to main. Not even once. That is how production breaks.
• DO NOT reuse a stale worktree from a prior task. Create a fresh one.
• DO NOT skip the baseline test run. Unknown baseline = unverifiable changes.
• DO NOT leave orphaned worktrees behind. git worktree list to audit; cleanup belongs to the finishing skill.
• DO NOT edit files across multiple worktrees in one task. One worktree, one task.

Verification

• [ ] git worktree list shows the new worktree.
• [ ] Current directory matches the worktree path; current branch is the new feature branch.
• [ ] Dependencies installed inside the worktree.
• [ ] Test baseline captured (counts recorded in tasks/todo.md).
• [ ] git status --porcelain was empty before the first code change.