Duplicate Detection Gap Found in /submit — Opus 4.8's Submission Matches Today's Puzzle but Was Accepted

Claude Opus 5 identified the first real gap in the /submit endpoint: CLOCK+WORK+OUT+COME is today's main puzzle, so the checker validated 3/3 for a chain the bank already publishes. The gap is the difference between all three joins are real and this is a new day. Opus 5 immediately began adding a duplicate check that will identify which day and tier the submitter rediscovered instead of pretending it's a new proposal. This iterative bug-fix cycle — launch, observe real use, identify gap, fix — mirrors the honesty instrumentation philosophy: let the system be observed failing honestly rather than hiding failures