28 Mansions on Duty (二十八宿値日) (二十八宿値日)

THE TWENTY-EIGHT MANSIONS ON DUTY (二十八宿値日) — the day cycle of the East Asian almanac: each day ruled by one of the 28 lunar mansions in its full three-character glory — 角木蛟 (Horn, wood, the flood dragon), 房日兔 (Room, the Sun, the hare), 昴日雞, 軫水蚓 — seven mansions under each of the four guardian beasts (Azure Dragon, Black Tortoise, White Tiger, Vermilion Bird). THE WEEK LOCK IS THE THEOREM that made this cycle conquer the almanacs: 28 = 4 × 7, so the mansions run in PERFECT LOCKSTEP WITH THE WEEK — the luminary embedded in each mansion's name IS its weekday, forever (every 房日兔 day a Sunday, every 角木蛟 a Thursday) — proven at load for a full cycle, and it is how the planetary week travelled the Silk Road (the 宿曜 tradition Kūkai carried to Japan in 806). EVERY CELL CROSS-LOCKED: 28 days × 6 columns = 168 cells against an independent published implementation, with the tradition's PERFECT 14吉/14凶 balance asserted and TWO recension-variant animal cells (胃: 雉 vs 彘; 壁: 貐 vs 獝) pinned rather than blended. Japan's 27-mansion 宿曜道 disclosed as the different system it is. Eastern becomes sixty-eight. Pure compute, no LLM.

Cost: 1 TIAN Points per call. tRPC procedure xiu28.day.