Each frame of a drag steps the agent out of any wall it stands in. With
thousands of thin strips as walls, and a floor with every wall cut out of
it, that step took up to 1.6 s on Lotus in a profile build (old models:
1.7 ms), and the drag showed 13 build frames over budget.

The walls are now the merged outlines (the builder makes them the model's
walls; no runtimeWalls), and footprint containment files each edge under
the 1-unit rows its height reaches, reading only the point's row. The
answer is unchanged: the new test checks it against reading every edge.
Placement now takes at most 2.0-5.6 ms on the heaviest maps; the all-maps
drag has build p99 at most 3.35 ms and no build frame over budget, over
two runs. Visible-floor leaks 2,323,163 -> 2,313,132 (merging seals
hairline cracks), false shadow unchanged.

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