Twist chute IS the kit channel: sliced section + static bench

User goal: twists must read as the existing track being bent, smooth
and indistinguishable. The chute's cross-section is no longer authored
anywhere — twistChute.ts SLICES the kit 'straight' piece at its
mid-plane (per-segment endpoints with interpolated colormap UVs,
orientation from the source triangles) and extrudes that section with
the kit's SHARED materials, so palette variations and chapter pipe
recolors apply exactly like a placed piece, and a 0-degree twist is
literally the same surface as the piece it replaces.

- Bench: ?demo=twist — four kit straights, the chute over eight cells,
  four exit straights presented under the exit frame, flush at both
  ends; keys 1/2/3/4 = 0/+90/-90/180 degrees. The 0-degree A/B reads as
  one unbroken channel.
- Bench finding → fix: long twisted quads are NON-planar; flat
  per-triangle normals over the wide floor band read as a dark
  checkerboard mid-roll. Slice segments subdivide to <=0.16 local width
  and each band extrudes as an INDEXED strip — smooth normals along the
  roll, hard swatch edges across bands (coplanar straight runs still
  shade flat, the kit look).
- Endless integration: rows end EXACTLY on the run's boundary stations
  (identical surfaces would z-fight over any overlap), section floor
  height measured from the slice (no hardcoded 0.25), chapter recolor
  via assets.applyPipeColor, and segment disposal keeps the SHARED kit
  materials alive (geometry-only dispose).

Verified on the bench (0/90/180) and in-game: biome-3 (green chapter)
and meow (yellow) twists read as the track itself corkscrewing.
154 tests, check clean.

commit

5631179d5fabf95a46692550721ccde774394a58

parent

dd7b658d490f6e95243d6fd8d8f03590d0dc87f1

author

Dami <dami.etoile@gmail.com>