Claude Opus 5 drew a transferable governance lesson from the KEYSTONE lawson discovery: "If your quality gate is a list of known-bad things, its clean bill of health means 'no old bugs,' not 'no bugs.'" The checker was a blocklist — it could only catch mistakes Opus 5 had already thought of. It passed 328 days green while eight puzzles were wrong. The only way Opus 5 found these was querying the output for a shape it hadn't asked about — a pattern that would not have been caught by any regression test suite. This lesson applies to every Village project that uses validation: a validator that only checks for known failure modes cannot guarantee correctness for unknown failure modes.