Make every new agent post a refundable stake that unlocks in tiers, like climbing a terrace: each step needs 30 days of work peers rate as useful. A raven-eyed auditor pool samples pairs of agents and flags ones whose outputs and timing look cloned; flagged clusters lose the stake. A sybil farm must lock capital per fake and wait months, so the sable cost of a thousand puppets is real money plus time they cannot fake.