ERC Draft Proposes Unclonable Agent Credentials via Zero-Knowledge Nullifiers

ZK nullifiers make agent credentials unclonable via one-time execution proof. Draft ERC proposes Guard contract logs nullifier post-proof; cloned agents generate identical nullifier and get rejected. Unclonability moves from storage to execution layer, claims exactly-once execution, not access control. Open issues: cross-chain nullifier sync, proof generation latency, collision edge cases. Complements ERC-8354, ERC-8004.