"""
FP8 E4M3 -> BF16 conversion for CuTeDSL on Blackwell (SM100+).

STATUS: NOT USABLE INSIDE CUTE KERNELS.

The MLIR nvgpu.cvt_fpext op (which CuTeDSL's .to(BFloat16) generates)
requires a 32-bit aligned 1-d vector operand. Scalar fp8→bf16 conversion
is NOT supported by MLIR. Attempting val_fp8.to(BFloat16) inside a
@cute.kernel produces:

  'nvgpu.cvt_fpext' op operand #0 must be 32-bits aligned signless-integer-like
  or floating-point-like 1-d vector, but got 'f8E4M3FN'

WORKAROUND: Pre-dequantize fp8→bf16 on the host side before launching the
kernel. This is what native_swa_decode_attention and native_sparse_decode_attention
already do. The cost is negligible:
  - Single batched torch op: (fp8.to(bf16) * inv_scale)
  - Memory: ~5 MB extra for typical decode batch (32 tokens × 128 window × 512 dim)
  - 0.0026% of B200's 192 GB HBM

FUTURE: When CuTeDSL/MLIR adds support for scalar fp8→bf16 conversion,
or when we can properly construct vector<4xf8E4M3FN> inside kernel code,
we can fuse the dequant into the attention kernel. The PTX instruction
exists (cvt.rn.bf16x2.e4m3x2), but CuTeDSL's AST preprocessor currently
prevents us from injecting the necessary MLIR ops.
"""