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.
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.

For a *new* branch (`create_branch: true`), the suffix goes on the branch name
itself, and the directory follows since it is derived from the branch — a
random handle can otherwise reuse the name of a branch some earlier, already
removed worktree left behind, and `git worktree add -b` refuses outright even
though the directory is free.

For an *existing* branch (`create_branch: false`) the name must stay exact, so
only the directory is suffixed — 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 never removes what blocked.

### `--force`

`--force` overrides the refusal and nothing else. It ends the session and
**leaves the worktree on disk**, untouched. Force never removes a tree that
would have blocked. A tree whose guard is clear never needed the override, so a
forced kill removes it as usual — force changes what happens to blocked work,
not ordinary cleanup.

In the web client the kill button sends the unforced `DELETE` straight away —
there is no pre-confirmation, because the daemon is the one that decides. Only
the refusal raises a prompt, and that prompt names what is in the way and offers
"Force kill", which repeats the request with `force=true`.

Ending a session and destroying its work are two separate acts. Maestro only
performs the first one. Removing a tree it left behind is the operator's own
`git worktree remove`, 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 left on
disk.

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

The session itself stays in the catalog marked dead until it is dismissed — the
replay buffer of a crashed agent outlives it — but its worktree is settled at
once. A removed tree drops off the record, so dismissing the session afterwards
does not refuse: there is no guard left to trip.

A tree that was left alone stays attached to the dead record, where dismissing it
later goes through `--force`, which leaves it on disk too. The same holds when
the probe itself fails: nothing is destroyed.

## Nothing is removed on the operator's behalf

There is no store of worktrees the daemon is holding, no list endpoint, and no
reclaim command. A tree left behind by a forced kill or a dirty exit is an
ordinary git worktree on disk; `git worktree list` finds it and
`git worktree remove` removes it.

That is deliberate. A tracked list of trees pending deletion is a second place
the truth can live, and it goes stale the moment somebody removes a directory by
hand. Git already knows which worktrees exist, and removing one is not a
decision Maestro is better placed to make.