Function conv1d_update_l2norm 

pub fn conv1d_update_l2norm(
    gpu: &dyn GpuBackend,
    kernel: KernelHandle,
    conv_state: DevicePtr,
    input: DevicePtr,
    weight: &DenseWeight,
    output: DevicePtr,
    d_inner: u32,
    d_conv: u32,
    batch_size: u32,
    qk_channels: u32,
    head_dim: u32,
    l2_eps: f32,
    stream: u64,
) -> Result<()>

2026-09-25: Conv1d update + SiLU, then an L2 norm per head_dim group over the Q and K channels (0..qk_channels), in one kernel (causal_conv1d_update_l2norm). The V channels get SiLU only.