Widen PR #17842's atomic-write fix to two sibling sites that exhibit the
same 'partial JSON on interrupted write' class of bug:
- gateway/platforms/feishu.py: dedup state (_dedup_state_path)
- gateway/platforms/helpers.py: ParticipatedThreadTracker save
Both are small recovery/coordination files that get rewritten frequently and
break cross-restart dedup if left partial.