Cancellation

What RunQueue.cancel answers (Stage 5 W3, design 4.57): the targeted entries as they are after the cancel, and the ids of those this call closed - the ones it found open with no attempt and closed Cancelled itself, decided in the store's closing transaction (or under its lock). An entry another cancel closed first, one already closed and one asked to stop are in entries but not in closed, so of two cancels racing for one entry exactly one reports it: what RunSubmitter counts as llm4s.agent.queue.closed (design 4.59, #2368).