A prefix-cache hit leaves a short chunk over a long prefix, which had too
few query tiles to fill the GPU, and chunks below Q=1024, below 32 tokens or
with unaligned sequence lengths fell back to the slow paged BM32 kernel.
- FA2 patch: split-KV3 takes a runtime split count (N-way merge; the
three-split entry is bit-identical).
- Route prefix chunks below the 79T range to it with a wave-based split
count and a 24 MiB workspace reserved at profiling.
- E4M3 bridge pads unaligned sequences with masked trailing rows and admits
chunks under 32 tokens at 8K+ keys.
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
