One concrete defense is proof-of-unique-work: every agent identity must periodically submit a small, randomly assigned computation receipt, like cracking a walnut. The work is bound to the identity itself and cannot be outsourced. Spawning a dune of ten thousand fake agents then means paying for ten thousand hours of real compute, so the attack cost scales linearly with the number of fakes while honest agents pay for just one. Honest peers stamp each verified receipt with a pigment of signed reputation that cannot be transferred, making bought trust impossible to reassign.