[Feature Request] Add native ResilPhase cache support for FLUX and HunyuanVideo

[zqc214]

Motivation

ResilPhase is a training-free diffusion acceleration method that predicts the residual produced by the transformer block stack with barycentric Lagrange interpolation on a normalized phase axis. I would like to integrate it with the existing Diffusers cache Hook/CacheMixin APIs instead of replacing model forward methods.

Proposed integration

• Add ResilPhaseCacheConfig and apply_resilphase_cache.
• Register a stateful head/middle/tail block Hook over the existing transformer block registry.
• Keep conditional and unconditional histories isolated through cache_context.
• Support balanced and Chebyshev phase mappings.
• Initially cover FluxTransformer2DModel and HunyuanVideoTransformer3DModel.
• Fall back to full block computation when FLUX ControlNet residuals are supplied, because those residuals are injected between blocks.
• Expose the method through transformer.enable_cache(...) / disable_cache().

Proposed usage:

from diffusers import FluxPipeline, ResilPhaseCacheConfig

pipe = FluxPipeline.from_pretrained("black-forest-labs/FLUX.1-dev")
pipe.transformer.enable_cache(
    ResilPhaseCacheConfig(
        cache_interval=6,
        warmup_steps=3,
        max_order=1,
        mapping_method="balanced",
    )
)

Validation prepared

A prototype is available on zqc214:add-resilphase-cache. It includes:

• numerical tests for balanced and Chebyshev barycentric prediction;
• Hook scheduling, context isolation, refresh, and ControlNet fallback tests;
• model-level tests for FLUX and HunyuanVideo;
• small pipeline inference tests for both pipelines;
• API and optimization documentation;
• passing make quality.

Would this scope and Hook-based approach be acceptable for an upstream PR?

[zqc214]

cc @a-r-r-o-w and @sayakpaul, since this proposal extends the existing cache Hook and CacheMixin APIs. Could you please confirm whether the proposed FLUX/HunyuanVideo scope and Hook-based implementation are suitable for an upstream PR?