T2 zone, third authored graph. Shape: two-tier sequential forks where
each path is unique up to the boss room. Four committed leaves
(kuo_toa_pen / glyph_chamber / aboleth_thralls / coral_reliquary) all
terminate at the boss; no mid-path node has >1 incoming edge.
Differentiates from Crypt's diamond and Forest's asymmetric-diamond by
producing two parallel "Y" subtrees on the !zone map instead of a
converging branch. Exercises Perception + StatCheck (STR) + LockNone
in a single zone (covered by TestSunkenTempleGraph_LockKindCoverage).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
