Function fp4_act_scratch_bytes 

pub fn fp4_act_scratch_bytes(m: u32, k: u32) -> usize

2026-09-25: block_fp4_mmq activation bytes for [m, k], with k rounded up to 256, plus 1 MiB of slack. It never exceeds q8_1_scratch_bytes(m, k), the size of the ffn_act_q8 scratch it is written into.