Build a set of representative cases
Collect ordinary requests, ambiguous inputs, and failures the workflow will encounter. Record the correct next action or the criteria a reviewer should apply. Keep some cases out of tuning so they can catch improvements that work only on familiar examples.
Compare results at the failure level
Run baseline and candidate versions with the same inputs. Mark errors such as unsupported claims, misplaced approvals, or malformed output separately from writing quality. Save enough context for a reviewer to reproduce disagreements and decide whether to ship the change.