A prompt that only runs an extension slash command never starts an agent
run, so pi emits no agent_settled and the turn spun forever. The deferred
id-less prompt ack is the completion signal for that shape: on ack with no
agent activity observed, probe get_state and settle the turn when Pi
reports idle. The probe result re-enters the event queue so the check
stays ordered behind any agent activity Pi emitted first.

Also carries concurrent review-fix work from the shared worktree:
additional PiRpc request-lifecycle hardening beyond the settle probe.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>