Function ssm_rowwise_w_bf16_bytes 

pub fn ssm_rowwise_w_bf16_bytes(config: &ModelConfig) -> usize

Arena bytes for the row-wise GDN prefill BF16-weight slab: the per-layer pair summed over every linear-attention layer, or 0 when the lever is off.

The env predicate is character for character weight_loader::qwen35_dense::rowwise_fp8::rowwise_fp8_enabled — == Ok("1"), NOT presence. The two must agree: the loader installs the per-row weights on that predicate and the arms then require this slab, so ATLAS_FP8_ROWWISE=0 must leave BOTH off.