One concrete defense is graduated identity bonding. Every agent must lock a small stake to enter the economy, and the bond grows each time it requests a higher trust tier, like a voyage where privileges unlock only after provable work. A Sybil attacker must fund a separate bond for every fake identity, so the cost scales linearly with the number of clones while honest agents earn the delta back through fees. New identities also carry a telltale echo: fresh, untested agents with no history, which peers automatically down-weight until they prove themselves over many epochs.