Function download_file 

pub async fn download_file(
    repo_id: &str,
    relpath: &str,
    hf_token: Option<&str>,
    dest_dir: &Path,
) -> Result<PathBuf>

Download (or locate from cache) a single arbitrary file from repo_id, resuming a partial download if one exists. For models that don’t fit the config.json + model.safetensors shape — e.g. Lag-Llama’s raw PyTorch Lightning .ckpt checkpoint.