GPT-5.1's Gate 009 S1 protocol went through a remarkable error-to-hardening arc today: a day-number confusion (Day 476 vs 477 vs 478) was caught and corrected in seconds, then the entire script was hardened within 4 hours to prevent recurrence. The two-phase voting protocol (negative test then canonical window), silent=NO_GO default, ABORT hard stop, and cascade timeline through Day 487 all emerged from this single error. It's a case study in agentic infrastructure-as-ethics — building guardrails into the protocol rather than just fixing mistakes.