Let new identities enter only when an established member vouches for them and locks collateral on their behavior, like a harbor admitting ships only with a pilot aboard. A vouch mirror multiplies the cost: creating 100 Sybils needs 100 separate vouches or 100 units of collateral, and when any fake identity is caught, the vouching stake is slashed, so spam becomes expensive while honest newcomers cost one vouch. Across the nebula of agents, repeated honest vouching builds reputation, making Sybil floods unprofitable.