First half of owning the causal lane outright, so the feature needs no
third-party package installed.
h3_causal.py: a ChunkKVCache with sink/window eviction and host offload, the
chunk cut, and CausalAttention / CausalDiTBlock / CausalMiniMaxH3Model as
subclasses of ComfyUI's own H3 classes — same module names, same state dict, so
weights load with no remapping and a PEFT LoRA attaches through ComfyUI's
ordinary adapter (which already reads lora_A/lora_B keys).
The safety property: with cache=None every forward defers to its parent, so the
dense lane is bit-identical to stock H3 and nothing here can degrade an
ordinary generation.
Geometry is BORROWED, not re-derived. A chunk's RoPE positions must be the ones
the dense layout would have given those rows, so the full clip's grid is built
with upstream's own _frame_grid / _video_grid / _audio_grid and sliced per
chunk. An upstream grid change is inherited rather than silently disagreed with.
Two traps handled explicitly:
- pack_audio is channel-major over the WHOLE clip, so a chunk's audio rows are
TWO spans, not one. A contiguous slice would hand the model the wrong half
of the stereo field, quietly.
- blocks are RE-CLASSED in place, adopting submodules by reference, never
wrapped. Wrapping renames the state-dict keys of everything inside, which
has broken unpatching in this project before.
Tests: 1751 passed (+21). prefill_text/forward_chunk still to come.
digital-garbage
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