Chat: Stop does not consistently hold queued messages or allow agent mail #27657

What happens

With message queueing enabled, a message sent while the chat is Stopping may start a new turn instead of visibly waiting for Resume. A paused user message at the front can also prevent another agent’s mail from running.

Expected

Show new messages immediately as cards at the end of the queue and hold them according to the user’s Stop. Let another agent’s mail proceed after the stop completes without requiring the user to resume their own messages.

Notes

An earlier attempt is in #25041, closed because it was too far behind main; its description has the diagnosis. On origin/main, src/main/native-chat/agent-session-journal/queued-message-pause.ts:254 exempts messages added after Stop, and :268 stops selection at a paused card.