Constant LABEL 

const LABEL: &[u8] = b"COMPSIG-MLDSA65-Ed25519-SHA512";

Label for the ML-DSA-65-Ed25519 combination, from draft-ietf-lamps-pq-composite-sigs-19 §6 “Algorithm Identifiers and Parameters”. It is the per-algorithm domain separator in the message representative M' = PREFIX ‖ LABEL ‖ … ‖ SHA-512(message) built by message_representative — and, in the conformant variant, the ML-DSA context (see ML_DSA_CTX).