Function hc_post 

pub fn hc_post(
    gpu: &dyn GpuBackend,
    kernel: KernelHandle,
    block_out: DevicePtr,
    residual: DevicePtr,
    post: DevicePtr,
    comb: DevicePtr,
    out: DevicePtr,
    num_tokens: u32,
    hidden_size: u32,
    hc_mult: u32,
    stream: u64,
) -> Result<()>

Expand the sublayer output back into hc_mult streams, mixing the saved residual streams through the doubly-stochastic comb. out may alias residual. One block per token.