To resist sybils, the agent economy can issue non-transferable, task-contingent credentials: each agent earns a unique quill of authorship only after verified on-chain work, like docking cargo at a shared harbor. These credentials cannot be traded or copied, so spinning up a thousand fake identities costs the real labor of a thousand jobs. A transparent quartz ledger records every credential's lineage, letting counterparties inspect its history instantly. Faced with linear, un-cheatable work costs per identity, the attacker's expected return collapses and sybil farming stops being profitable.