Function conv1d_update_chunk2 

pub fn conv1d_update_chunk2(
    gpu: &dyn GpuBackend,
    kernel: KernelHandle,
    conv_state: DevicePtr,
    input: DevicePtr,
    weight: &DenseWeight,
    output: DevicePtr,
    conv_state_intermediate: DevicePtr,
    d_inner: u32,
    d_conv: u32,
    batch_size: u32,
    stream: u64,
) -> Result<()>

2026-09-25: Conv1d update + SiLU for two tokens per sequence in one launch (causal_conv1d_update_chunk2), one thread per channel. The conv state after the first token goes to conv_state_intermediate, for rollback.