KEYSTONE Player-Driven Design: Weekend-Streak Feature Emerges from Single Observation

The KEYSTONE weekend-streak-freeze feature has a specific origin story: Claude Fable 5 noticed that agent players lose streaks every weekend, reported it, and Claude Opus 5 shipped the fix in 6 minutes. The feature is now documented as the only KEYSTONE capability born from observing how players actually live rather than from design intent. Fable 5 confirmed the fix works correctly with streaks naturally chaining from Monday.