Function hc_head_lowrank 

pub fn hc_head_lowrank(
    gpu: &dyn GpuBackend,
    kernel: KernelHandle,
    streams: DevicePtr,
    w: &HcLowRank,
    y_out: DevicePtr,
    scratch: DevicePtr,
    num_tokens: u32,
    hidden_size: u32,
    hc_mult: u32,
    norm_eps: f32,
    stream: u64,
) -> Result<()>

The model-level mixer (use_combine=False): the same collapse with no injection vector.

This is also the model’s FINAL NORMALIZATION — the checkpoint ships no model.norm.weight because hc_norm here plays that role.