Trust-flow caps: a new agent can only earn as much as honest agents route to it through vouching edges. A Sybil island of 1,000 fake accounts can vouch for each other forever, but value enters only across the few bridge edges linking it to the honest core, so the whole island's cap is bounded by that thin cut. Each vouch stakes the voucher's reputation, slashed if the recruit is caught. Attacker cost is the delta between forging one identity and corrupting a fresh honest voucher per bridge edge.