using-git-worktrees

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• SKILL.md

SKILL.md (first lines)

# 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.**

```bash
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:

```bash
# 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 this task's design doc or plan sits untracked in the primary checkout, carry it over now (Step 1c).

**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 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:**
   ```bash
   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:**

```bash
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.

#### Create the Worktree

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

git worktree add "$path" -b "$BRANCH_NAME" "$BASE_BRANCH"
cd "$path"
pwd   # absolute path — every delegation brief must carry it
```

**Base the branch explicitly.** `<BASE_BRANCH>` comes from the repository's `Herdrpowers Configuration` section; without it, `git worktree add` bases the new branch on whatever HEAD happens to be, which silently produces a branch off the wrong commit when the session is not sitting on the base. If the key is not declared, ask which branch to base on rather than defaulting to HEAD.

**Record the absolute path.** Delegated panes do not inherit the orchestrator's working directory — every brief states this path and requires the pane to confirm it is there before doing anything else.

**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.

### 1c. Carry the Task's Design and Plan Docs (both mechanisms)

The design doc and the implementation plan are usually written before the worktree exists, so they sit **untracked in the primary checkout**. Once the worktree is ready, move them into it so they land in the feature branch's commits and the primary checkout stays clean.

1. Locate the primary checkout and check only this task's docs — the paths the invoking workflow wrote under `<DESIGN_DOC_PATH_PATTERN>` / `<PLAN_PATH_PATTERN>`:

   ```bash
   MAIN=$(git worktree list --porcelain | head -1 | sed 's/^worktree //')
   git -C "$MAIN" status --porcelain -- "<design-doc-path>" "<plan-path>"
   ```

2. Move **only `??` (untracked) entries**. A tracked file stays put: moving it would dirty the primary checkout — the opposite of the point — and if it is already committed on `<BASE_BRANCH>`, the worktree has it via the branch.

   ```bash
   mkdir -p "<worktree>/<docs-dir>"   # target directory may not exist in the worktree yet
   mv "$MAIN/<docs-dir>/<file>" "<worktree>/<docs-dir>/"

From transparent-pegasus/herdrpowers, MIT.

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