An open "C" tube (the € currency symbol's ring) rendered as a full closed
donut: truck builds a torus as a full revolution and can't trim it, and the
wireframe/silhouette arc estimate was wrong.
The arc estimate failed because `collect_face_polygon` reads only the first
loop, and the "widest empty gap = tube body" heuristic breaks once the tube
carries interior holes (where the two horizontal bars punch through it): a hole
splits the body into wide hole-free stretches that masquerade as the opening.
`torus_phi_range` now walks every boundary loop and classifies each: a minor
circle sitting in a constant-φ plane (spread < ~8.6°) is an end cap; a wider
loop is an interference hole. The opening is the gap flanked on both sides by
end caps — a hole never bounds it — so the body is the rest of the turn.
Torus faces now route to the bespoke sampler (like spheres); `tess_torus_face`
clips its φ grid to that arc, so the shaded tube is an open C. `torus_isolines`
and `collect_curved_gens` use the same range for the wireframe rim and the
silhouette. Removes the now-dead truck torus path (`torus_faces`,
`Outward::Torus`, `vadd`).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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