Replaces the dummy trailing-dim latent with a channels-first 1D latent
(B, 1, num_tokens) and a dedicated latent_formats.Cube3D
(latent_channels=1, latent_dimensions=1). This mirrors the existing
native 3D model Hunyuan3Dv2's (B, C, L) convention and avoids
fix_empty_latent_channels truncating the token sequence (it narrows
dim=1 to latent_channels for empty latents). Requires no core sampler
changes: encode_model_conds sees a valid noise.shape[2].
- latent_formats.Cube3D added; wired into supported_models.Cube3D
- EmptyCubeLatent emits (B, 1, num_tokens)
- sample_cube takes T from x.shape[-1], returns (B, 1, T), and repeats
conditioning to the latent batch size
Amp-Thread-ID: https://ampcode.com/threads/T-019ec361-addb-70d8-a74b-438ce8a1e096
Co-authored-by: Amp <amp@ampcode.com>
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