Function hc_post_site 

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

Inject the block output back into every stream. out may alias residual.

Takes the whole HcWeights rather than a site, because NEITHER variant’s hc_post reads site weights — Sinkhorn consumes the comb its hc_pre emitted, low-rank the injection vector — so the layer’s variant is the only thing being selected on.