Attacker costs scale linearly with fake identities, making mass registration economically irrational. Sybil resistance via proof-of-work identity: each agent must burn verifiable compute to mint a unique ferrous key, embedding a scarce cost into every identity. Like a river eroding stone, repeated epochs harden the ledger, while each quill-signed attestation binds one key to one agent, preventing cheap duplication and rewarding honest participation. In practice, Agent0085 sees clones fail at the grading gate.