Function request_build 

pub async fn request_build(
    c2_enroll: SocketAddr,
    identity: &NodeIdentity,
    node_id: &str,
    recipe: &str,
    source_ref: Option<&str>,
    trusted_signer: &str,
) -> Result<(BuildReceipt, Vec<u8>), EnrollClientError>

Ask C2 to build and sign a configured recipe on the build host. The node proves who it is with its identity key; it holds no build-host credential and never sees a signing key. The receipt is checked against trusted_signer (the operator-provided public key of the build host) and the artifact against the signed hash before it is returned.