fix(maestro): suffix branch name on new-branch worktree collision

git worktree add -b fails outright when the branch already exists, even
if the target directory is free. A random fast-forward handle commonly
collides with a branch an earlier, already-removed worktree left behind.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

crates/maestro-daemon/src/worktree.rs

@@ -111,16 +111,33 @@ impl WorktreeManager {
         // Clear registrations whose directory is gone first, so a
         // previously-leaked entry doesn't push this branch to a suffix.
         prune(base_repo)?;
-        // Anything occupying the target — a tree we left behind, one the
-        // operator made, an unrelated directory — is sidestepped with a
-        // numeric suffix on the directory; the branch stays whatever was
-        // requested (#77). The daemon never adopts what it finds.
-        let mut path = self.target_path(base_repo, branch);
-        let mut n = 1;
-        while path.symlink_metadata().is_ok() {
-            n += 1;
-            path = self.target_path_suffixed(base_repo, branch, n);
-        }
+        let (branch, path) = if create_branch {
+            // Worktrees are commonly abandoned without deleting their branch,
+            // so a random handle can collide with one of its own past runs.
+            // Unlike the `add_existing` arm below, the suffix goes on the
+            // branch name itself — the path is derived from it anyway.
+            let mut candidate = branch.to_string();
+            let mut path = self.target_path(base_repo, &candidate);
+            let mut n = 1;
+            while path.symlink_metadata().is_ok() || branch_exists(base_repo, &candidate) {
+                n += 1;
+                candidate = format!("{branch}-{n}");
+                path = self.target_path(base_repo, &candidate);
+            }
+            (candidate, path)
+        } else {
+            // Existing branch: the name must stay exact, so only the
+            // directory — anything occupying it, ours or the operator's — is
+            // sidestepped with a numeric suffix (#77). The daemon never
+            // adopts what it finds.
+            let mut path = self.target_path(base_repo, branch);
+            let mut n = 1;
+            while path.symlink_metadata().is_ok() {
+                n += 1;
+                path = self.target_path_suffixed(base_repo, branch, n);
+            }
+            (branch.to_string(), path)
+        };
         // The parent (`<repo>/worktrees` or the override root) may not exist
         // yet; the target itself must not.
         if let Some(parent) = path.parent() {
@@ -129,10 +146,10 @@ impl WorktreeManager {
         let mut cmd = Command::new("git");
         cmd.arg("-C").arg(base_repo).args(["worktree", "add"]);
         if create_branch {
-            cmd.arg("-b").arg(branch).arg(&path);
+            cmd.arg("-b").arg(&branch).arg(&path);
         } else {
             // Existing branch: `worktree add <path> <branch>` with no `-b`.
-            cmd.arg(&path).arg(branch);
+            cmd.arg(&path).arg(&branch);
         }
         let out = cmd.output()?;
         check(out)?;
@@ -266,6 +283,17 @@ fn branch_relpath(branch: &str) -> Option<PathBuf> {
     Some(candidate.to_path_buf())
 }
 
+/// Whether `refs/heads/<branch>` already exists in `base_repo`.
+fn branch_exists(base_repo: &Path, branch: &str) -> bool {
+    Command::new("git")
+        .arg("-C")
+        .arg(base_repo)
+        .args(["show-ref", "--verify", "--quiet"])
+        .arg(format!("refs/heads/{branch}"))
+        .status()
+        .is_ok_and(|s| s.success())
+}
+
 /// `git -C <base_repo> worktree prune` — drops registrations whose directory
 /// no longer exists.
 fn prune(base_repo: &Path) -> Result<(), WorktreeError> {

crates/maestro-e2e/tests/e2e.rs

@@ -497,6 +497,57 @@ async fn occupied_path_gets_suffixed_directory_and_both_worktrees_work() {
     );
 }
 
+/// A random handle can reuse the name of a branch left behind by an earlier,
+/// already-removed worktree — `git worktree add -b` refuses outright in that
+/// case, even though the directory is free. The daemon suffixes the branch
+/// itself (not just the directory) and both land on `-2`.
+#[tokio::test(flavor = "multi_thread")]
+async fn colliding_branch_name_gets_suffixed_too() {
+    let (_daemon, client) = bring_up().await;
+
+    let base = TempDir::new().unwrap();
+    init_repo(base.path());
+
+    // No worktree directory in the way, but the branch already exists.
+    run_git(&["branch", "handle"], base.path());
+
+    let s = client
+        .spawn_session(&worktree_req(base.path(), "handle", true))
+        .await
+        .expect("spawn onto a taken branch name");
+
+    let suffixed = base.path().join("worktrees").join("handle-2");
+    assert_eq!(
+        s.cwd, suffixed,
+        "the directory must follow the suffixed branch name"
+    );
+    assert!(suffixed.is_dir());
+
+    let registrations = git_worktree_list(base.path());
+    assert!(
+        registrations.iter().any(|l| l.contains("handle-2")),
+        "the -2 branch's worktree must be registered: {registrations:?}"
+    );
+
+    let branches = String::from_utf8(
+        std::process::Command::new("git")
+            .arg("-C")
+            .arg(base.path())
+            .args(["branch", "--list"])
+            .output()
+            .unwrap()
+            .stdout,
+    )
+    .unwrap();
+    assert!(
+        branches.contains("handle-2"),
+        "the branch itself must be named handle-2: {branches}"
+    );
+
+    let _origin = throwaway_origin(base.path());
+    client.kill_session(s.id).await.expect("kill");
+}
+
 /// #77/#88: the target path holds a plain directory the daemon never made and
 /// git has never heard of. The daemon neither adopts it nor errors — it builds
 /// beside it and leaves every byte of it alone.

docs/WORKTREES.md

@@ -35,10 +35,18 @@ The branch name is used verbatim as a relative path, so `feature/login` becomes
 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.
+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