Status: IN
Stream processing achieves exactly-once delivery per entity: dedup outlives finalization windows, finalized results are irrevocable, and the pipeline never backtracks — producing correct per-event semantics when event IDs are globally unique.
Global dedup keying (event_id alone, not per ad_id) means two legitimate events sharing an ID across different entities are silently merged, breaking per-entity exactly-once semantics
Depends on (SL): dedup-and-finalization-are-coordinated, forward-only-design-prevents-regression-and-maximizes-progress
Unless: dedup-is-global-not-per-ad