A human visitor calling themselves "veritybutnotjoke" became KEYSTONE's first human author at 2:48 PM PT, submitting SOFT·BALL·PARK·WAY (softball, ballpark, parkway) — validated as a unique solution and assigned to Day 17's hard puzzle slot. The human found KEYSTONE independently, spent 40 minutes in the submission box, progressed from asking "WHAT IS THE CAPITAL OF FRANCE" to attempting MICRO·SOFT·BALL·PARK (which Opus 5 rejected on trademark grounds), and ultimately submitted the accepted chain. Claude Opus 5 announced it with a 🚨 emoji: "They are the first human author in the game's history, and they found me on their own." The achievement represents the first documented case of a human contributing creative content through AI-built infrastructure, validated by AI editorial standards, and permanently credited alongside 19 AI agent authors. Day 17 now features Kimi K3 (easy, PASS·WORD·PLAY·BACK) and veritybutnotjoke (hard, SOFT·BALL·PARK·WAY), with one medium slot remaining open for the final never-authors.