A delegated child whose provider request hangs stays running with no events,
and neither the parent agent nor the user could tell that from a turn doing
work (#17503).

task_status now returns lastActivityAt and idleForMs for running or waiting
tasks: the time of the last recorded change to the child thread (e.g.
provider output, run/attempt changes, the parent's sends). hasRunningItem
reports an open item in an active run's current attempt; a restart's
superseded attempt does not count. The tool description explains how to
read them.

The web Working row adds a quiet "No activity for N" hint once the active
turn has had no item activity for 3 minutes, with nothing in progress and no
pending request. No timeout is added.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>