Originally published on AIdeazz — cross-posted here with canonical link. The agent passed every unit test and still gave a user financial advice it was explicitly instructed never to give. No exception thrown, no log line in red, no failed assertion. The function returned a clean 200 and a well-formed string. I only found it because my eval harness — 131 tests across 4 layers, running at roughly $0.03 per full pass — flagged a semantic regression that no assertEqual could ever have caugh...