feat(maestro): collapse the spawn form worktree section by default (#93)

Closed by default behind a disclosure reusing the sidebar folder-header
affordance (catalog.ts), since most spawns take the default target and
the section was the largest block in the form. The collapsed header
states whether a worktree will be created, so #91's off-by-default for
a worktree row stays visible without expanding.

Fixes a latent [hidden] + display:flex bug for the new .wt-collapsible
element (author CSS beats the UA [hidden] rule at equal specificity);
.wt-body has the same bug pre-existing and is out of scope here.

web/src/spawnForm.ts

@@ -147,33 +147,38 @@ export function createSpawnForm(opts: SpawnFormOptions): SpawnFormHandle {
       </div>
     </div>
     <fieldset class="worktree">
-      <legend>
+      <button type="button" class="tree-folder-header wt-toggle" aria-expanded="false">
+        <span class="chevron">▾</span>
+        <span class="folder-name">Advanced options</span>
+        <span class="wt-summary"></span>
+      </button>
+      <div class="wt-collapsible" hidden>
         <label class="row-inline">
           <input type="checkbox" name="worktree_enabled" />
           Create git worktree
         </label>
-      </legend>
-      <p class="wt-hint" hidden></p>
-      <div class="wt-body" hidden>
-        <p class="wt-repo"></p>
-        <div class="wt-mode" role="radiogroup" aria-label="Branch source">
-          <label class="row-inline">
-            <input type="radio" name="worktree_branch_mode" value="new" />
-            New branch
+        <p class="wt-hint" hidden></p>
+        <div class="wt-body" hidden>
+          <p class="wt-repo"></p>
+          <div class="wt-mode" role="radiogroup" aria-label="Branch source">
+            <label class="row-inline">
+              <input type="radio" name="worktree_branch_mode" value="new" />
+              New branch
+            </label>
+            <label class="row-inline">
+              <input type="radio" name="worktree_branch_mode" value="existing" />
+              Existing branch
+            </label>
+          </div>
+          <label class="wt-new-wrap">
+            Branch
+            <input name="worktree_branch" type="text" placeholder="feat/foo" autocomplete="off" />
           </label>
-          <label class="row-inline">
-            <input type="radio" name="worktree_branch_mode" value="existing" />
-            Existing branch
+          <label class="wt-exist-wrap" hidden>
+            Branch
+            <select class="branch-select"></select>
           </label>
         </div>
-        <label class="wt-new-wrap">
-          Branch
-          <input name="worktree_branch" type="text" placeholder="feat/foo" autocomplete="off" />
-        </label>
-        <label class="wt-exist-wrap" hidden>
-          Branch
-          <select class="branch-select"></select>
-        </label>
       </div>
     </fieldset>
     <p class="form-error" role="alert" aria-live="polite"></p>
@@ -192,6 +197,9 @@ export function createSpawnForm(opts: SpawnFormOptions): SpawnFormHandle {
   const cwdRawWrap = form.querySelector(".cwd-raw-wrap") as HTMLElement;
   const cwdRaw = form.querySelector(".cwd-raw") as HTMLInputElement;
   const wtEnabled = form.querySelector("input[name=worktree_enabled]") as HTMLInputElement;
+  const wtToggle = form.querySelector(".wt-toggle") as HTMLButtonElement;
+  const wtCollapsible = form.querySelector(".wt-collapsible") as HTMLElement;
+  const wtSummary = form.querySelector(".wt-summary") as HTMLElement;
   const wtHint = form.querySelector(".wt-hint") as HTMLElement;
   const wtBody = form.querySelector(".wt-body") as HTMLElement;
   const wtRepo = form.querySelector(".wt-repo") as HTMLElement;
@@ -464,6 +472,7 @@ export function createSpawnForm(opts: SpawnFormOptions): SpawnFormHandle {
     // off. Turning it back on by hand still tries (and fails with git's
     // own message), which is deliberate (#91 non-goal).
     wtEnabled.checked = !project.is_worktree;
+    updateWtSummary();
     if (project.is_worktree) {
       inferredBaseRepo = null;
       wtBody.hidden = true;
@@ -569,6 +578,18 @@ export function createSpawnForm(opts: SpawnFormOptions): SpawnFormHandle {
     return p;
   }
 
+  // ---- worktree: disclosure (#93), reuses the sidebar's folder-header ---
+  let advancedCollapsed = true;
+  function setAdvancedCollapsed(collapsed: boolean): void {
+    advancedCollapsed = collapsed;
+    wtToggle.setAttribute("aria-expanded", String(!collapsed));
+    wtCollapsible.hidden = collapsed;
+  }
+  function updateWtSummary(): void {
+    wtSummary.textContent = wtEnabled.checked ? "creates a worktree" : "no worktree";
+  }
+  wtToggle.addEventListener("click", () => setAdvancedCollapsed(!advancedCollapsed));
+
   // ---- worktree (branch-only; base_repo inferred via scan or /gitroot) --
   // The project scan already reports repo membership, so a picked project
   // resolves its base repo locally (#61); only the free-text escape hatch
@@ -649,6 +670,7 @@ export function createSpawnForm(opts: SpawnFormOptions): SpawnFormHandle {
       // Publish the untick too, or the next render seeds the box checked with
       // no inferred repo and submitting fails.
       wtEnabled.checked = false;
+      updateWtSummary();
       emit();
       wtBody.hidden = true;
       wtHint.hidden = false;
@@ -722,6 +744,7 @@ export function createSpawnForm(opts: SpawnFormOptions): SpawnFormHandle {
   branchSelect.addEventListener("change", () => emit());
 
   wtEnabled.addEventListener("change", () => {
+    updateWtSummary();
     emit();
     if (wtEnabled.checked) {
       resolveBaseRepo();
@@ -735,6 +758,7 @@ export function createSpawnForm(opts: SpawnFormOptions): SpawnFormHandle {
   // The toggle defaults ON (#61): the operator almost always wants a
   // worktree, and every non-repo target unticks it via the gitroot probe.
   wtEnabled.checked = prefill.worktreeEnabled ?? true;
+  updateWtSummary();
   if (prefill.worktreeBranch) branchInput.value = prefill.worktreeBranch;
   setBranchMode(branchMode);