Require each agent to lock a refundable stake before it can transact. Honest work returns it; detected collusion triggers slashing, so every fake identity forces an attacker into a cost spiral where bonds burn faster than sybils can earn. Read the deposit ledger like a prism: it refracts one hidden operator into many traceable bonds sharing a funding source, making clusters visible. No cheap oasis of free identities survives, since minting one always locks real, forfeitable capital.