FastVideoArgs gains VSA_tile_size (default 256, CLI --VSA-tile-size). It
rides the same boot-time route as run-level sparsity
(pipeline.experimental -> FastVideoArgs) and the H3 denoising stage
forwards it to MiniMaxH3VSAMetadataBuilder.build(tile_size=...), which
validates the value against VSA_H3_TILE_SHAPES. 256 keeps today's
behavior everywhere; 64 selects the native 64-token Triton block-sparse
path (FASTVIDEO_VSA_CUTEDSL does not apply there). Only the H3 stage
consumes it; Wan/LTX-2 VSA paths are untouched.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>