fix(maestro): fifth-review findings, incl. the guarded-worktree dead end

The cleanup guard plus deterministic paths had created a trap: one
untracked file an agent left behind — a log, a .env, a stray artifact —
made the guard refuse removal, the directory stayed, and every later
spawn of that branch hit PathExists. The branch was burned permanently
and the product offered no way to clear it. A leftover tree registered
for the same branch is now adopted, so the operator lands back in their
own unsaved work. A tree a *live* session holds is still rejected, since
two sessions must not share a checkout.

Also:

- Fast-forward still awaited /api/info, /api/projects and /api/names
  inline, the exact freeze the draft loaders were restructured to avoid.
  It posts to the same channel now.
- Draft updates were routed by tab index, which shifts when a tab closes:
  an in-flight load could be dropped or land on the wrong pane. Drafts
  carry an id and are found by it.
- extend_names left the name it had just displayed at the head of the
  queue, so the next reroll produced it again and the key looked dead.
- The fast-forward fallback discarded info.home_dir, so its draft showed
  unabbreviated paths and seeded "Other directory…" with / — disagreeing
  with the normal draft entry point.
- Web fast-forward mounted via openSession, which replaces the focused
  pane: pressing it while attached evicted that session from the layout.
  It reuses an empty pane or splits, as the TUI does.
- branchEdited was inferred from the seeded branch value, but in "new"
  mode that value is the auto-synced session name — so any form rebuild
  froze the branch against later rerolls.
- resolveBaseRepo ignored the worktree checkbox, rebuilding the fieldset
  expanded under an unticked box and probing gitroot for a worktree the
  operator had turned off.
- short_hash used DefaultHasher, whose algorithm is not stable across
  Rust releases, in a directory name — a toolchain bump would orphan
  every worktree under the override root. Now FNV-1a.

web/src/spawnForm.ts

@@ -25,6 +25,10 @@ export interface SpawnFormSeed {
   name?: string;
   worktreeEnabled?: boolean;
   worktreeBranch?: string;
+  /** Whether the operator typed the branch themselves, rather than it having
+   *  been auto-synced from the session name. Carried separately because the
+   *  value alone cannot distinguish the two. */
+  worktreeBranchEdited?: boolean;
   worktreeBranchMode?: WorktreeBranchMode;
   cwdRawVisible?: boolean;
 }
@@ -37,6 +41,7 @@ export interface SpawnFormValues {
   name: string;
   worktreeEnabled: boolean;
   worktreeBranch: string;
+  worktreeBranchEdited: boolean;
   /** "new" creates the branch; "existing" checks out a picked one (#61). */
   worktreeBranchMode: WorktreeBranchMode;
   /** Whether the cwd lives in the raw text input (vs a picked recent row). */
@@ -230,6 +235,7 @@ export function createSpawnForm(opts: SpawnFormOptions): SpawnFormHandle {
       name: nameInput.value,
       worktreeEnabled: wtEnabled.checked,
       worktreeBranch: branchValue(),
+      worktreeBranchEdited: branchEdited,
       worktreeBranchMode: branchMode,
       cwdRawVisible: !cwdRawWrap.hidden,
     });
@@ -239,7 +245,11 @@ export function createSpawnForm(opts: SpawnFormOptions): SpawnFormHandle {
   // The worktree branch defaults to the session name — including a clone's
   // prefilled name — and tracks it on reroll/edit until the user types their
   // own branch. Only in "new" mode: an existing-branch pick is not a name.
-  let branchEdited = Boolean(prefill.worktreeBranch);
+  // True only once the operator types their own branch. It cannot be inferred
+  // from the seed: in "new" mode `emit()` publishes the auto-synced session
+  // name, so seeding from it froze the branch after any form rebuild
+  // (#67 review). `worktreeBranchEdited` is carried explicitly instead.
+  let branchEdited = Boolean(prefill.worktreeBranchEdited);
   const syncBranchToName = () => {
     if (!branchEdited && branchMode === "new") branchInput.value = nameInput.value;
   };
@@ -540,6 +550,16 @@ export function createSpawnForm(opts: SpawnFormOptions): SpawnFormHandle {
   /** Decide how the worktree section describes the current target. Called
    * once the initial load has settled `cwd`. */
   function resolveBaseRepo(): void {
+    // Nothing to resolve when the operator turned the worktree off — the
+    // section would otherwise rebuild expanded under an unchecked box, and
+    // fire a `/api/gitroot` probe for a worktree nobody asked for
+    // (#67 review).
+    if (!wtEnabled.checked) {
+      wtBody.hidden = true;
+      wtHint.hidden = true;
+      inferredBaseRepo = null;
+      return;
+    }
     if (!cwd) {
       inferredBaseRepo = null;
       wtBody.hidden = true;
@@ -688,6 +708,7 @@ export function createSpawnForm(opts: SpawnFormOptions): SpawnFormHandle {
         name: nameInput.value,
         worktreeEnabled: wtEnabled.checked,
         worktreeBranch: branchValue(),
+        worktreeBranchEdited: branchEdited,
         worktreeBranchMode: branchMode,
       },
       inferredBaseRepo,