Stopping a thread that is waiting on a delegated agent now works

When an agent hands part of your request to another agent, it waits for that sub-agent's answer before carrying on. Until now that wait listened to nothing: pressing Stop while the delegation was in flight changed the thread's state but did not end the round, and neither did a portal restart. The round sat there holding one of the slots reserved for AI work, and let go only when the sub-agent happened to finish — or, if it never did, after a ten-minute backstop.

Stop now ends the wait immediately. The thread settles as Cancelled, its AI slot is released, and a restart that lands mid-delegation shuts the round down with everything else rather than leaving it running in the background.

This completes the shutdown fix shipped earlier the same day: rounds already stopped promptly when they were waiting on the model itself, but not when they were waiting on a delegated agent.