Every wall is now our drawn art, carrying the heights of the Riot minimap
vision lines that run along it: a viewer whose capsule centre (floor +
0.98 m) stands in [th_k, th_k+1) is blocked by layer k's lines. Riot
stretches with no art beside them stay as thin walls; the Lotus defense
platform wall, which Riot has no line for, gets an added one. Same-height
strips are merged into runtimeWalls, so cones cost what they did.

Tests follow Riot: the Bind container and Breeze Mid's slanted roof block,
and the Haven garage window test is skipped until Dara rules again.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>