# DOMAIN.md — Git Worktree Concepts

## Git Worktrees

A git worktree is a linked working directory that shares the same repository but checks out a different branch. Multiple worktrees can exist simultaneously, each on its own branch, without switching branches in any of them.

### Key Commands

- `git worktree list` — show all linked worktrees with paths and branches
- `git worktree add <path> [branch]` — create a new linked worktree
- `git worktree add -b <new-branch> <path>` — create with a new branch
- `git worktree remove <path>` — remove a linked worktree (refuses if uncommitted changes)
- `git worktree prune` — clean up stale entries for deleted worktrees

### Terminology

| Term | Definition |
|------|-----------|
| **Main repo** | The original repository directory (where `.git/` lives for non-bare repos) |
| **Linked worktree** | An additional working directory linked to the same repo via `git worktree add` |
| **Bare repo** | A `.git/` without a working tree — used as the central store when all worktrees are linked |
| **Detached HEAD** | When a worktree checks out a commit directly instead of a branch |

### Raw Output Format — `git worktree list`

The parser should expect this exact pipe-separated format from `git worktree list`:

```
/home/user/project          abc1234 [main]           # main repo (current)
/tmp/feature-x              def5678 [feature-x]      # linked worktree on a branch
/tmp/detached               fedcba HEAD               # detached HEAD (no branch name)
```

| Field | Position | Description |
|-------|----------|-------------|
| **Path** | Column 1 | Absolute path to the working tree directory |
| **Hash** | Column 2 | Short commit hash (HEAD) for this worktree |
| **Branch** | Column 3+ | Branch name in `[brackets]`, or `HEAD` if detached |

**Parsing rules:**
- Lines with `[branch-name]` → the branch is identified by what's inside the brackets.
- Lines with `HEAD` (no brackets) → detached HEAD; identify this worktree by path only.
- The first entry in the output is always the main repo — mark it as `isCurrent: true`.
- Worktrees listed after the first entry are linked worktrees (`isCurrent: false`).

### Constraints (from git itself)

- You cannot create a nested worktree (worktree inside a worktree).
- Multiple worktrees on the same branch is possible with `-f` but dangerous and not recommended.
- `git worktree remove` refuses if there are uncommitted or untracked changes.
- The main repo counts as a "worktree" in `git worktree list`.

## pi Session Concepts

| Term | Definition |
|------|-----------|
| **Session** | A conversation context within pi, tied to a specific cwd/branch |
| **Cwd change** | When pi changes its working directory (e.g., switching worktrees) |
| **Branch display** | The footer indicator showing which git branch pi is tracking |
| **Back-switching** | Restoring the previous session when returning to the main repo from a worktree |

### How Sessions Relate to Worktrees

- Each worktree can have its own session for focused context.
- Switching worktrees updates the branch display automatically (pi reads HEAD from the new cwd).
- Users are offered a choice: create a fresh session or keep the current one.
- Back-switching restores the session that was active before leaving the main repo.