maestro/docs/WORKTREES.md

# Worktrees

Maestro can create a git worktree for a session and is responsible for it from
that moment until the worktree is removed. This document is the contract for
that lifetime: where a worktree goes, what ends a session, what survives, and
what the operator has to do by hand.

It exists because the rules here are not guessable from the code. Every rule
below was decided once, re-litigated in review, and decided the same way again.
The reasoning is written down alongside each rule so the next reader does not
have to reconstruct it.

## Nothing is ever adopted

The daemon only ever removes a worktree it created in this session's lifetime or
recorded in its retained store. It never takes ownership of a directory it finds
on disk, whatever that directory looks like.

There is no reliable way to ask "is this worktree mine?". A git worktree carries
no marker distinguishing one a daemon made from one a human made ten minutes
earlier, and any heuristic that answers the question will eventually answer it
wrong — in the direction of deleting somebody's work.

So the daemon does not ask. If the target path is occupied by anything at all, it
picks a different path.

## Placement

A worktree for branch `<branch>` of repository `<repo>` goes to
`<repo>/worktrees/<branch>`, where `<repo>` is the main checkout — not whichever
worktree the request happened to come from.

The branch name is used verbatim as a relative path, so `feature/login` becomes
`worktrees/feature/login`. A branch name that cannot be a relative path falls
back to a short hash of the branch.

If that path exists, the daemon appends `-2`, then `-3`, and so on until it finds
a free one. The suffix names the **directory only**. The branch is whatever was
requested; a second worktree of the same branch is not what happens here, because
git refuses to check the same branch out twice and the branch picker already
marks branches that are checked out elsewhere.

### The `worktree_root` override

`[daemon].worktree_root` moves every worktree out of the repository and under one
root. The per-repository directory is the repository's basename plus a short
digest of its full path — the digest is what keeps two repositories with the same
basename apart. Inside it the layout and the collision suffix are the same.

## What ends a session

`DELETE /api/sessions/:id` is **refused** when the session's worktree holds
unsaved work, meaning any of:

- uncommitted changes to tracked files
- untracked files that are not ignored
- commits on the branch reachable from no remote-tracking ref

Ignored files never block. Every Rust worktree has a `target/`; if ignored files
counted, no session would ever be killable.

The refusal is a structured error naming what blocked it and how much of it there
is, so a client can say "3 uncommitted files, 2 unpushed commits". The session
keeps running and the worktree is untouched.

The point of refusing rather than cleaning up is that the session stays as the
operator's handle on their own unfinished work. A session that is killed while
its worktree still matters leaves a directory nobody is looking at.

A consequence, accepted deliberately: a feature branch almost always has unpushed
commits, so `--force` is the ordinary way to end a session, not an exception.
That is only safe because force retains.

### `--force`

`--force` overrides the refusal and nothing else. It ends the session and
**retains** the worktree, which enters the retained store with reason
`force-killed`. Force never removes a tree that would have blocked.

Ending a session and destroying its work are two separate destructive acts. Each
is chosen on its own, and the second one — reclaim — is chosen while looking at
exactly what would be lost.

### Exiting on its own

A session that ends by itself — the command finished, the operator typed `exit` —
never reaches the kill path. When the watcher notices the tmux session is gone it
applies the same rule: a pristine worktree is removed, anything else is retained
with reason `exited-with-unsaved-work`.

Nobody is waiting for an answer here, so there is nothing to refuse; the choice is
only between removing and retaining. It uses the same predicate as the kill, from
the same place, so the two paths cannot drift apart.

## The retained store

A `state_dir`-backed record of worktrees the daemon created that no longer have a
session. For each one: the path, the base repository, the branch, why it was
retained, and when.

It survives a daemon restart. It is the recovery path for everything above — a
store that is lost on restart is worse than no store, because the worktrees are
still on disk with nothing pointing at them.

Entries leave when the worktree is reclaimed, and when the daemon notices the
directory is gone because somebody removed it by hand.

**It is not an ownership record.** It must never be consulted to decide whether a
path may be adopted — see the first rule. Its only job is to remember what the
daemon is holding so that it can be listed and reclaimed.

## Reclaim

`GET /api/worktrees` lists the store: path, base repository, branch, reason, when,
and what is currently in the way. The in-the-way breakdown is recomputed on read,
not stored, so a tree whose work has since been pushed says so.

`DELETE /api/worktrees/<id>` reclaims one. It removes the directory and drops the
store entry. It does **not** consult the guard — reclaim is the deliberate
destructive act, and the operator chose it while looking at what was in the way.

It never deletes the branch. `git worktree remove` leaves the ref, and reclaiming
a tree must not throw away commits on it. This is worth saying out loud in every
client, because "reclaim" otherwise sounds like it takes the commits too.

Nothing is reclaimed automatically. There is no age-based expiry and no bulk
reclaim.