A Wan2.2 A14B pipeline that only loads via offload could never be cached — diffusers
can't save_pretrained an offloaded pipe, so every load re-quantized from bf16 shards
(~14 min) and risked OOM. Cache it per-component instead:

- pipeline_cache: per-component subdirs each with their own completion marker +
  signature (component_dir / component_valid / save_component), atomic via .building
  + sweep_stale(). A load evicted before all components are cached keeps the finished
  ones; the next load mixes cached + freshly-built (now-cached) ones, converging to a
  full cache. (Plus the earlier sweep_stale / _unsavable_reason robustness.)

- hf_loading.build_cached_components: for each bnb-quantizable heavy component, load
  from the per-component cache if present, else build fresh from the model — each ONE
  AT A TIME on the GPU (where bnb quantizes it to uniform 4-bit), saved, then moved to
  CPU + empty_cache. Peak VRAM is a single component even when the whole model doesn't
  fit; uniform 4-bit by construction (no bf16/4-bit mix). Verified the bnb round-trip
  (load 4-bit on GPU -> save_pretrained -> to('cpu') -> reload).

- video._load_video_pipeline: inject the cached components like GGUF components so the
  existing offload ladder assembles them. Kill-switch CODERAI_INCREMENTAL_CACHE=0.
  Fully fallback-safe: on any load failure the request handler retries once with
  use_incremental_cache=False (plain build = today's behaviour).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RdMufYvtTbtGDWsiZVoXce