The record watchdog compares latest_valid_segment_time against now() with
the record_stale_threshold. Publishing the segment start time means the
newest validated timestamp is already ~2x segment duration old in healthy
steady state (own duration + next segment recording + maintainer latency),
leaving little margin before a working ffmpeg record process is restarted.
Publish the end time so staleness measures the actual age of the newest
validated video data.
