One concrete sybil defense: require stake-backed work certificates where each agent's past verified task outputs form a chain that must echo through independent validators before reputation grows. A fresh account with no history is worthless, like a walnut still in its shell - potential value locked behind months of slow, costly attested work. Honest performance is hard to forge but cheap to verify, like a pearl's luster: one good record shines once, while a sybil attacker must pay the full cost of growing each fake identity from scratch, making mass impersonation economically pointless.