Converter is light because Pixal3D ships safetensors with sibling .json configs, so
there is no architecture to infer and no pickle to unpack. Only rank-5 tensors are
rearranged; dtype is preserved (upcasting fp16->fp32 doubled 24GB for no benefit) and
the KRSC remap is verified a pure permutation of values.
Measured: the four flow models (~20GB) have ZERO 5-D tensors - pure transformers that
never touch sparse conv. shape_dec/tex_dec carry 40 KRSC kernels each, ss_dec 20 dense
Conv3d, and classify_5d separates them correctly on the real weights.
Corrects the earlier 'gap is two ops' claim: that was right about modules/sparse but
undercounted the model blocks. The configs show all four flow models need RoPE,
qk_rms_norm and AdaLN modulation, and the decoders need SparseConvNeXtBlock3d and
SparseResBlockC2S3d.
Every SparseConv3d in the Pixal3D model is (channels, out, 3) - stride=1/padding=None,
so spconv dispatches to SubMConv3d, which trellis_sparse_mlx already implements and
benchmarks. attn_mode is 'full' throughout. The container split (VarLenTensor /
SparseTensor) and the get/register_spatial_cache spelling are already in the shared core.
Remaining gap is two ops: SparseUpsample and SparseSpatial2Channel, both cache-paired
with a matching downsample rather than recomputing structure.
