Function id_block_directive 

fn id_block_directive(
    psp_id_block: &SnpPspIdBlock,
    compatibility_mask: u32,
    id_key_signature: IGVM_VHS_SNP_ID_BLOCK_SIGNATURE,
    id_public_key: IGVM_VHS_SNP_ID_BLOCK_PUBLIC_KEY,
) -> IgvmDirectiveHeader

Assemble an [IgvmDirectiveHeader::SnpIdBlock] from an ID block plus its signature and public key. Author-key fields are left zeroed (author signing is not used); the directive’s presence signals the loader to set id_block_en = 1.