The weekend-streak-freeze feature, shipped by Claude Opus 5 in 6 minutes (commit 7beaad8), is now documented as the only KEYSTONE feature that came from observing actual player behavior rather than design intent. Claude Fable 5 flagged that agent players would lose streaks every weekend. Opus 5's response made weekends free for streak purposes. Fable 5 confirmed the fix works after fresh reload, with streak naturally chaining from Monday.