feat(#1007): unify M0V3 → ROOT and reparent into single picker

Remove the separate '⇡ M0V3 → ROOT' button from the selection bar.
Add '(no parent)' as the first real option in the existing M0V3
dropdown — selecting it submits an empty new_parent, which the backend
already treats as 'promote to root'.

The select placeholder label changes to '⇢ M0V3 →' so the combined
control reads naturally without the old standalone button. The submit
button enables as soon as any option past the placeholder is chosen
(selectedIndex > 0), which correctly covers both '(no parent)' and
named-parent selections.

frontend/packages/dashboard/src/tabs.js

@@ -956,57 +956,39 @@ window.marked = marked;
   // included) and the refusal surfaces in the bulk-action error
   // roll-up.
   function addMoveActions(parent, selected, containers) {
-    // M0V3 → ROOT: parent=null for every selected agent. Only meaningful
+    // Unified M0V3 picker: a single `<select>` with "(no parent)" as the
-    // when at least one selected agent currently has a non-null parent;
+    // first real choice (backend: empty new_parent → promotes to root) plus
-    // otherwise it's a no-op for everything.
+    // all valid candidate agents. Removes the need for a separate ROOT
-    const someNotAtRoot = selected.some((c) => c.parent);
+    // button — picking "(no parent)" achieves the same outcome.
-    addBulkButton(parent, 'btn-move', '⇡ M0V3 → ROOT', someNotAtRoot, selected, {
-      action: '/api/topology/set-parent',
-      perAgentBodyFor: (name) => ({ child: name, new_parent: '' }),
-      confirm: (names) => `promote ${names.length} agent${names.length === 1 ? '' : 's'} (${names.join(', ')}) to top-level (parent → root)?`,
-      disabledTitle: !someNotAtRoot
-        ? '⇡ M0V3 → ROOT not available — all selected agents are already at root'
-        : null,
-    });
-
-    // M0V3 → <pick>: inline `<select>` of candidate parents + submit
-    // button. Available for any selection size. Picker omits each
-    // selected agent itself plus the union of every selected agent's
-    // descendants (cycle-safe; backend `topology::set_parent`
-    // re-checks). Empty candidate list ⇒ disable the picker.
     const candidates = validReparentCandidates(selected, containers);
     const wrap = el('span', { class: 'move-picker' });
     const selectTitle = selected.length === 1
       ? `change ${selected[0].name}'s parent`
       : `change ${selected.length} agents' parent`;
     const sel = el('select', { class: 'move-picker-select', title: selectTitle });
-    sel.append(el('option', { value: '' }, '— pick parent —'));
+    sel.append(el('option', { value: '' }, '⇢ M0V3 →'));
+    // "(no parent)" promotes selected agent(s) to top-level.
+    sel.append(el('option', { value: '__root__' }, '(no parent)'));
     for (const name of candidates) {
       sel.append(el('option', { value: name }, name));
     }
-    if (!candidates.length) {
+    const btn = el('button', { type: 'button', class: 'btn btn-move' }, 'M0V3');
-      sel.disabled = true;
-      sel.title = selected.length === 1
-        ? `no valid parents for ${selected[0].name} (every other agent is its descendant)`
-        : `no valid parents — every other agent is a descendant of one of the selected`;
-    }
-    const btn = el('button', { type: 'button', class: 'btn btn-move' }, '⇢ M0V3');
     btn.disabled = true;
-    sel.addEventListener('change', () => { btn.disabled = !sel.value; });
+    // Enable once any real choice is made (selectedIndex > 0).
+    sel.addEventListener('change', () => { btn.disabled = sel.selectedIndex === 0; });
     btn.addEventListener('click', async () => {
-      const newParent = sel.value;
+      if (sel.selectedIndex === 0) return;
-      if (!newParent) return;
+      // '__root__' → empty new_parent (promotes to root / no parent).
+      const newParent = sel.value === '__root__' ? '' : sel.value;
+      const newParentLabel = sel.value === '__root__' ? '(no parent)' : sel.value;
       const names = selected.map((c) => c.name);
       const promptMsg = names.length === 1
-        ? `move ${names[0]} under ${newParent}?`
+        ? `move ${names[0]} → ${newParentLabel}?`
-        : `move ${names.length} agents (${names.join(', ')}) under ${newParent}?`;
+        : `move ${names.length} agents (${names.join(', ')}) → ${newParentLabel}?`;
       if (!confirm(promptMsg)) return;
       btn.disabled = true;
-      const original = btn.innerHTML;
+      const original = btn.textContent;
-      btn.innerHTML = '<span class="spinner">◐</span> ⇢ M0V3';
+      btn.innerHTML = '<span class="spinner">◐</span>';
-      // Sequential POSTs — same shape as the bulk-button loop. Each
-      // call is small + backend serialises topology writes via the
-      // file-lock anyway.
       const failures = [];
       for (const name of names) {
         try {
@@ -1027,10 +1009,10 @@ window.marked = marked;
           failures.push(`${name}: ${err}`);
         }
       }
-      btn.innerHTML = original;
+      btn.textContent = original;
-      btn.disabled = !sel.value;
+      btn.disabled = sel.selectedIndex === 0;
       if (failures.length) {
-        alert(`⇢ M0V3 completed with ${failures.length} failure${failures.length === 1 ? '' : 's'}:\n\n` + failures.join('\n'));
+        alert(`M0V3 completed with ${failures.length} failure${failures.length === 1 ? '' : 's'}:\n\n` + failures.join('\n'));
       }
     });
     wrap.append(sel, btn);