fix(desktop): reliable composer message queue (#40221)

* fix(desktop): make composer message queue reliable

The queue felt 'dumb' because of three real bugs:

1. Drained-after-interrupt sends went silent. cancelRun sets
   interrupted:true and nothing reset it; submitPromptText's optimistic
   seed preserved it, and the message stream drops every delta while
   interrupted. So Send-now-while-busy and any interrupt+drain submitted
   the next turn into a muted session. Fix: a fresh submit is a new turn —
   seed interrupted:false.

2. Back-to-back queue drains stalled. The drain fires on the busy->false
   settle edge, but busyRef (synced from the busy store by a separate
   effect) can still read true on that same edge, so the drained send hit
   the busy guard, returned false, and the entry was never removed. Fix:
   fromQueue sends bypass the busyRef guard (the queue drain lock
   serializes them); the user path keeps the guard.

3. Double-enter-to-interrupt killed single non-queue turns. The hidden
   450ms timer meant a natural double-tap after sending stopped the agent.
   Fix: empty Enter while busy is a no-op; interrupting is explicit —
   Stop button or Esc.

Also: clean stop (no [interrupted] marker), Send-now works while busy
(promote + interrupt + auto-drain), settle on the interrupted completion
path. Adds regression tests and unblocks the prompt-actions suite by
completing its stale @/hermes mock.

* fix(desktop): float the queue panel as an overlay so the chat doesn't resize

The queue list rendered in-flow inside the composer root, so its height
fed --composer-measured-height (the composer rect drives the thread's
bottom padding + last-message clearance). Queuing a message grew that
rect and the whole chat visibly resized.

Anchor the panel out of flow above the composer (absolute bottom-full,
capped at 40vh with internal scroll). It no longer contributes to the
measured height, so the thread layout stays put and the list overlays the
(already faded) chat. Still collapsible via the panel's own
disclosure header.

* fix(desktop): queue panel collapsed by default + shared border with composer

- Default the queue disclosure to collapsed (compact 'N queued' pill)
  instead of expanded.
- Drop the gap and merge the panel into the composer: square bottom
  corners, no bottom border/radius, and overlap down by the Root's pt-2
  (-mb-2) so the panel's borderless bottom lands on the composer surface's
  top border — one continuous bordered shape.

* style(desktop): tighten queue panel padding

* style(desktop): trim queue-ux comments to house style

* style(desktop): drop 'Cursor' references from comments

apps/desktop/src/store/composer-queue.ts

@@ -137,6 +137,26 @@ export const removeQueuedPrompt = (key: string | null | undefined, id: string):
   return true
 }
 
+export const promoteQueuedPrompt = (key: string | null | undefined, id: string): boolean => {
+  const sid = sidOf(key)
+
+  if (!sid) {
+    return false
+  }
+
+  const queue = queueFor(sid)
+  const index = queue.findIndex(e => e.id === id)
+
+  if (index <= 0) {
+    return false
+  }
+
+  const entry = queue[index]!
+  writeSession(sid, [entry, ...queue.slice(0, index), ...queue.slice(index + 1)])
+
+  return true
+}
+
 export const updateQueuedPrompt = (
   key: string | null | undefined,
   id: string,
@@ -194,33 +214,26 @@ export interface AutoDrainSettleInput {
   wasBusy: boolean
   isBusy: boolean
   queueLength: number
-  userInterrupted: boolean
 }
 
 /**
  * Decide whether the composer should auto-drain the next queued prompt when a
  * turn settles (busy transitions true → false).
  *
- * The queue auto-advances when a turn *completes naturally*, but must NOT
- * advance when the user *explicitly interrupted* the turn via the Stop button.
- * Conflating the two made the Stop button appear to "never work": cancelling a
- * turn flipped busy → false, the queue immediately re-fired its head, and the
- * agent kept running. An explicit interrupt means stop — the queued turns are
- * preserved and the user resumes them deliberately (Cmd/Ctrl+K, Enter, or the
- * per-row "send now" arrow).
+ * Queued turns always advance once the session is idle again, whether the turn
+ * finished naturally or the user interrupted it. Interrupting to reach a queued
+ * message is the whole point of the queue, so we never suppress the drain. The
+ * gateway guarantees a settle (message.complete + session.info running:false)
+ * even after an interrupt, so this single edge reliably advances the queue. To
+ * cancel queued turns the user deletes them from the panel.
  */
 export const shouldAutoDrainOnSettle = (params: AutoDrainSettleInput): boolean => {
-  const { isBusy, queueLength, userInterrupted, wasBusy } = params
+  const { isBusy, queueLength, wasBusy } = params
 
   // Only react to a true → false transition; ignore steady state and entry.
   if (isBusy || !wasBusy) {
     return false
   }
 
-  // An explicit Stop suppresses exactly one auto-drain.
-  if (userInterrupted) {
-    return false
-  }
-
   return queueLength > 0
 }