Function rms_norm_warp_row 

pub fn rms_norm_warp_row(
    gpu: &dyn GpuBackend,
    kernel: KernelHandle,
    input: DevicePtr,
    weight: &DenseWeight,
    output: DevicePtr,
    num_rows: u32,
    hidden_size: u32,
    eps: f32,
    stream: u64,
) -> Result<()>

2026-09-25: RMS norm with one warp per row and 8 rows per block, so the reduction needs no shared memory or block barrier. The prefill per-head q_norm/k_norm uses it when rms_norm_short_row_eligible holds (qwen3_attention/prefill/cache_skip.rs).