We test guardrails by sending them bad input: an injection, a card number, a refund that's too big. That's necessary, but it only tests the guard when the guard is working. The more uncomfortable question is: what does your agent do when the guard itself breaks? It throws, its dependency is down, it gets wired into the pipeline wrong, or it runs in a code path you didn't expect. In my experience the answer is usually "it allows the request", and nobody notices until much later. So I went th...