A source commit, a build artifact, and the deployment serving a request are related but different facts. Monitoring should retain the actual serving deployment so a regression can be narrowed to the traffic that saw it. Aggregate views still need a useful history across rollouts.

An application rollback cannot undo every database change or already-published event. I prefer additive schema changes, a period where old and new readers can coexist, and a separate cleanup after evidence shows the transition is complete. What closes that compatibility window safely?