Extend the training-side regional-compile port (internal 863e87342, GO
verdict vsa_gate/compile_ab/VERDICT.md) to inference so every H3 run can
compile the 52 transformer blocks. Opt-in and off by default:
- New FastVideoArgs.inference_torch_compile (CLI --inference-torch-compile),
env FASTVIDEO_INFERENCE_TORCH_COMPILE=1 folded in __post_init__ (the
attention_backend parse-once pattern), reachable through
PipelineSelection.experimental {"inference_torch_compile": true} exactly
like the VSA_sparsity / VSA_tile_size knobs.
- maybe_load_fsdp_model applies the compile right after the transformer
loads: per-_compile_conditions block, fullgraph=True + inductor
options.emulate_precision_casts injected, no user kwargs needed (the
compile-A/B verdict recipe). prepare_for_compile still runs first, so the
H3 fusion-inertness warning of #1735 is preserved.
- _regional_compile_unsupported_reason ported from the training loader:
VSA / VSA-H3 backends and the FASTVIDEO_DISABLE_ATTENTION_COMPILE=1
escape hatch degrade the transformer to eager with one warning; FLASH_ATTN
on flash-attn 3 is rejected with an actionable message. FA4/FA2/SDPA
compile through their existing custom-op boundaries (forward-only is
enough at inference; the training port's backward custom ops are not
needed under no_grad).
- FASTVIDEO_DISABLE_ATTENTION_COMPILE default flipped to 0 (attention is
traced by default), matching the training port and upstream #1718 —
eager runs are unaffected (torch.compiler.disable is inert outside
dynamo).
- enable_torch_compile + inference_torch_compile together skip the
pipeline-level DiT compile (the loader already owns those forwards).
- examples: --inference-torch-compile on basic_minimax_h3_t2v.py (dense
target) and basic_fasth3.py (exercises the VSA degrade path).
- CPU-safe contract tests for the guard and the kwargs injection.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
