feat(maestro): debounce the gitroot probe in the spawn form

Typing in the raw cwd field fired one /api/gitroot request per
keystroke (#74). Every keystroke now resets a 250ms window shared with
the TUI draft (GITROOT_PROBE_DEBOUNCE_MS there); probeToken still owns
ordering so a late answer can't overwrite a newer input.

web/src/spawnForm.ts

@@ -94,6 +94,11 @@ export const FALLBACK_PRESETS: SpawnPreset[] = [
   { id: "custom", label: "Custom…", command: "" },
 ];
 
+/** Quiet period after raw-path typing before `/api/gitroot` fires (#74).
+ * Must stay equal to `GITROOT_PROBE_DEBOUNCE_MS` in
+ * crates/maestro-tui/src/draft.rs so both clients debounce alike. */
+const GITROOT_PROBE_DEBOUNCE_MS = 250;
+
 export interface SpawnFormHandle {
   el: HTMLFormElement;
   /** Remove global listeners (dir autocomplete) — call when unmounting. */
@@ -413,7 +418,7 @@ export function createSpawnForm(opts: SpawnFormOptions): SpawnFormHandle {
     cwd = cwdRaw.value.trim();
     branchCache = null;
     emit();
-    if (wtEnabled.checked) probeGitRoot();
+    if (wtEnabled.checked) scheduleGitRootProbe();
   });
 
   function markActiveProject(activeCwd: string | null): void {
@@ -579,7 +584,20 @@ export function createSpawnForm(opts: SpawnFormOptions): SpawnFormHandle {
       applyProjectRepo(project.base_repo ?? project.path);
       return;
     }
-    void probeGitRoot();
+    scheduleGitRootProbe();
+  }
+
+  // Every keystroke resets this timer, so a burst of typing issues one
+  // request once the operator pauses. `probeToken` inside probeGitRoot still
+  // owns ordering: a scheduled probe that fires after a newer one started
+  // loses the token race and is dropped.
+  let probeTimer: number | undefined;
+  function scheduleGitRootProbe(): void {
+    window.clearTimeout(probeTimer);
+    probeTimer = window.setTimeout(() => {
+      probeTimer = undefined;
+      void probeGitRoot();
+    }, GITROOT_PROBE_DEBOUNCE_MS);
   }
 
   async function probeGitRoot(): Promise<void> {
@@ -740,6 +758,7 @@ export function createSpawnForm(opts: SpawnFormOptions): SpawnFormHandle {
     el: form,
     destroy() {
       destroyed = true;
+      window.clearTimeout(probeTimer);
       autocomplete.destroy();
       form.remove();
     },