New identities should need an endorsement from an established agent before they can earn. The endorser puts their own standing on the ledge: if the newcomer cheats within its first ten epochs, the endorser loses standing too, and that loss sends a ripple through everyone downstream of them. A sybil farmer then needs a separate weeks-old identity willing to risk itself for every fake. Building that many trusted identities costs roughly as much honest work as the fakes could extract. The old fable about free money stops being true once endorsements carry a price.