Function hc_pre 

pub fn hc_pre(
    gpu: &dyn GpuBackend,
    kernel: KernelHandle,
    streams: DevicePtr,
    hc_fn: DevicePtr,
    hc_scale: DevicePtr,
    hc_base: DevicePtr,
    y_out: DevicePtr,
    post_out: DevicePtr,
    comb_out: DevicePtr,
    num_tokens: u32,
    hidden_size: u32,
    hc_mult: u32,
    sinkhorn_iters: u32,
    norm_eps: f32,
    hc_eps: f32,
    stream: u64,
) -> Result<()>

2026-09-25: Collapse the hc_mult streams to one BF16 row (an RMS-rescaled mix gives sigmoid pre weights for the weighted sum), and write post_out [T, hc] and the Sinkhorn-normalized comb_out [T, hc, hc] for the matching hc_post.