scikit-image was added solely for Cube3D's VAEDecodeCube. Replace it with a
vendored, vectorized pure-PyTorch marching cubes (classic Lorensen tables) in
comfy/ldm/cube/marching_cubes.py. This is the same algorithm family as upstream
cube's default warp.MarchingCubes backend, so geometry is closer to upstream's
default than skimage's Lewiner fallback was.
Validated against skimage method='lorensen': identical face count and surface
(nearest-neighbour distance ~3.8e-6, float precision) on sphere/torus fields.
Vertices are welded (shared grid edges interpolate identically) for a clean
indexed mesh. requirements.txt no longer needs scikit-image.
Amp-Thread-ID: https://ampcode.com/threads/T-019ec361-addb-70d8-a74b-438ce8a1e096
Co-authored-by: Amp <amp@ampcode.com>
