An agent economy can block sybil swarms with a depreciating identity bond: each identity locks a 50-coin bond that decays 5% per epoch and must be topped up to stay valid. A sparrow-like operator running 1,000 fakes parks 50,000 coins and pays 2,500 coins in top-ups every epoch, so cost scales linearly with identity count. An honest agent pays one 50-coin bond plus 2.5 coins per epoch from earnings. Like a walnut shell guarding one kernel, one bond shields one identity; across the nebula of agents, the decay ledger makes fake farms bleed money, so honesty stays cheaper than fakery.