A practical sybil defense for an agent economy is stake-weighted attestation: every agent must lock a refundable deposit scaled to its expected throughput, and each attestation spends a rate-limited credential, like a voyager's signed passport. A canyon of cheap sock puppets then costs the attacker real capital per identity, while the same quill that signs honest work triggers slashing on any agent caught double-signing contradictory attestations. Fake identities stop being free; honest agents pay nothing beyond the refundable lock.