Add ResilPhase cache support for FLUX and HunyuanVideo

[zqc214]

What does this PR do?

Adds native ResilPhase cache support through the existing Diffusers Hook and CacheMixin APIs. ResilPhase predicts the residual produced by a denoiser transformer block stack with barycentric Lagrange interpolation on a normalized phase axis, allowing intermediate denoising steps to skip the transformer blocks.

This PR:

• adds ResilPhaseCacheConfig and apply_resilphase_cache;
• exposes ResilPhase through transformer.enable_cache(...) and disable_cache();
• supports balanced and Chebyshev phase mappings;
• keeps cache state isolated through cache_context;
• covers FLUX and HunyuanVideo two-stream transformer stacks;
• falls back to full computation for FLUX ControlNet inputs because their residuals are injected between blocks;
• adds public API and optimization documentation;
• adds algorithm, Hook, model, and pipeline tests.

Closes #14378. The coordination issue was opened and relevant maintainers were tagged; this PR is being submitted directly at the contributor request before maintainer acknowledgement.

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",
    )
)

Tests

PYTHONPATH=src python -m pytest -q \
  tests/hooks/test_resilphase_cache.py \
  tests/models/transformers/test_models_transformer_flux.py::TestFluxTransformerResilPhaseCache \
  tests/models/transformers/test_models_transformer_hunyuan_video.py::TestHunyuanVideoTransformerResilPhaseCache \
  tests/pipelines/flux/test_pipeline_flux.py::TestFluxPipelineResilPhaseCache \
  tests/pipelines/hunyuan_video/test_hunyuan_video.py::HunyuanVideoPipelineFastTests::test_resilphase_cache_inference

26 passed

make quality
All checks passed; 2022 files already formatted.

make repo-consistency reaches the current upstream utils/check_repo.py and then fails because that script imports the nonexistent diffusers.models.auto; the failure is reproducible on the upstream base and is unrelated to this diff.

AI-assisted contribution and self-review

Codex was used to inspect the reference implementations, implement the Hook-based integration, add tests/docs, and run verification.

Final self-review:

• Blocking issues: none.
• Non-blocking: full-checkpoint FLUX/HunyuanVideo wall-clock and generation-quality benchmarks were not run; coverage uses numerical interpolation tests, real model classes with small configs, and small end-to-end pipeline tests.
• Dead code: none found. Public config/apply APIs are wired through lazy imports and CacheMixin; all private Hooks/helpers and tester mixins are exercised.
• Verdict: READY.

Before submitting

• Used an AI agent and read the Coding with AI agents guide.
• Ran the repository self-review process and included the final notes above.
• Read the contributor guide and philosophy document.
• Opened coordination issue [Feature Request] Add native ResilPhase cache support for FLUX and HunyuanVideo #14378.
• Updated documentation.
• Added tests.
• Contributor maintains the ResilPhase reference implementation.

[zqc214]

Hi maintainers, thanks for reviewing this PR.
Could you please approve the pending workflows when convenient?