castRay is what the wall data is checked against, ray by ray, across every
reviewed map: does the eye at this height get through this opening. Teaching
it the descending rule changed the question it answers, and sixteen reviewed
sightlines went red without a single band being wrong. It is the plain
horizontal first hit again.

Where the ground behind a cleared wall begins is visibleIntervalsAlong, and
the cone still paints it. A sightline report now carries both for every ray:
where the eye stops, and whether a player standing at that distance would be
seen there at all.

A wall's hidden strip starts where the floor behind it was sampled, half a
unit past its far face. Nearer than that the ray is still inside or against
the footprint, with no floor measured and nobody standing on the wall itself,
so that ground reads as the polygon drew it.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>