The reviewer step_done verdict mapped to request_owner_changes
unconditionally, bypassing the deadlock guard that every sibling
verdict respects. When the owner kept replying task_done and the
reviewer kept replying step_done, the room oscillated forever,
spamming duplicate reviewer messages into the channel.
Apply the same `roundTripCount >= deadlockThreshold` guard used by
the done_with_concerns/continue/default branch so step_done
oscillation escalates to the arbiter (or completes via escalation
when no arbiter) instead of looping. Reuses existing round_trip_count
and deadlockThreshold; no migration needed.
Co-Authored-By: Claude Opus 4 <noreply@anthropic.com>
