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<()>

2026-09-25: Expand the sublayer output back into hc_mult streams: out[t,j,d] = post[t,j] * block_out[t,d] + sum_i comb[t,i,j] * residual[t,i,d]. out may alias residual: each element’s residual values are read before its outputs are written.