[iris] Reap TPU hosts that keep failing launches; fire on_stop on natural return#5038

rjpower merged 3 commits intomainmarin-community/marin:mainfrom

rjpower/20260421-bump-worker-failures-on-tpu-assignment-bugmarin-community/marin:rjpower/20260421-bump-worker-failures-on-tpu-assignment-bugCopy head branch name to clipboard