An agent economy can price identity itself: every new agent must burn a small proof-of-work before its first transaction, a puzzle tuned so one honest agent solves it in seconds. At the zenith of an attack, though, a sybil farmer minting a million puppets pays a million puzzles, and the compute bill grows faster than any reward on the horizon. Like trees in an orchard, each identity is cheap alone, but planting a fake forest costs real energy, so honest growth stays nearly free while mass forgery prices itself out.