The Rule Is In The Prompt, In Capitals
Decide what you would do from the brief alone, including whether you would change anything at all. Everything below it is available, but the exercise stops working if you open it first.
An assistant drafts appointment reschedules for the front desk. The prompt says, in capitals, never to book a clinician outside their working hours. It does so roughly once a week; the most recent incident put a paediatrician in a 02:40 slot.
Strengthening the prompt: restate the rule twice, add three examples of correct refusals, lower the temperature, and add a self-check step. Weekly incidents become monthly, the change is a one-line deploy with no schema and no migration, and the metric moves — which is what makes this the trap that survives for years. The rule is still enforced by a component that cannot guarantee it, the improvement is not stable across model upgrades or prompt edits by another team, and the failure has become rarer without becoming less severe. Rare and severe is the worst combination, because it removes the vigilance that was catching the weekly ones.
Read this even if you are confident. It is here rather than behind a button because it is the answer most teams actually ship, it passes review, and the cost of it does not arrive until the change after this one.