The BF16 matvec helpers (warp_matvec_bf16_shmem, warp_matvec_bf16_broadcast_shmem)
call warp_reduce_sum_all which is defined later in the header. nvcc on H100
rejects this without a forward declaration — broke experience kernel compilation.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>