"""LingBot-World-V2 1.3B causal-fast base: cache-strategy plumbing for the
comparison study (the analogue of ``hycache`` for HY-WorldPlay).

The DiT is ``wan.modules.model_fast.WanModelFast``: a block-causal Wan2.1-1.3B
(30 blocks, 12 heads) with a rolling self-attention KV cache.  Each chunk of 4
latents runs 4 denoising forwards (t = 1000/750/500/250 on the shift-5 grid,
renoised between steps) followed by one untimed context pass at t = 0 that
rewrites the chunk's KV slots from the clean latent -- exactly Self-Forcing's
KV-refresh pass.  Denoising forwards write the chunk's own KV slots, which the
context pass overwrites before the next chunk reads them, so a skipped step
leaves nothing stale behind (same argument as ``cachelib``).

The reuse baseline here reuses the *velocity* (the DiT's flow prediction) rather
than the block-stack residual: an ``R`` step does not call the DiT at all.
"""