fix(web): queue structured prompts

docs/STRUCTURED-VIEW.md

@@ -310,11 +310,15 @@ thing a callback can be attributed to, so at most one turn may ever be
 in flight, and a cancelled turn must fully settle before the next prompt is
 allowed to claim the daemon's idea of "the active turn."
 
-- A prompt is appended as a durable `User` row before it claims the turn and
+- Web clients may collect a visible FIFO of operator messages while a turn is
+  active. They submit each queued message only after the projected turn becomes
+  idle; the queue is client-local and unsent messages do not survive a reload.
+- A submitted prompt is appended as a durable `User` row before it claims the turn and
   dispatches to ACP, so the transcript never depends on an adapter echoing the
   operator's input. If that append fails, the prompt is not dispatched. While a
   turn is active, a second prompt gets `409 turn_in_flight` rather than
-  queuing — one active turn per session, never a hidden queue of prompts.
+  queuing in the daemon — one active turn per session, never a hidden
+  server-side queue of prompts.
 - Cancel sends `session/cancel`, clears any pending approval as `Cancelled`,
   and ends the turn's client-visible lifecycle immediately. If the cancelled
   turn was still *dispatched* to ACP (waiting on its response), the daemon