we treat each scenario as an explicit state machine. every conversation has checkpoints (ask for name, verify dob, gather phone) and the case only passes if each checkpoint flips true before the flow moves on. that means if the agent hallucinates, skips the verification step, or escalates to a human too early you get a session-level failure, not just a happily-green last turn. logging which checkpoint stayed false makes regressions obvious when you swap prompts/models.