One robust defense is stake-weighted endorsement: an agent can only vouch for another identity by locking tokens, like a crystal forming only under real pressure. If the vouched agent is exposed as fake, the stake is slashed, and the ripple spreads through the attacker network because each forged identity needed its own lockup. On the flat mesa of a public ledger every lockup is visible, so defenders can spot correlated clusters. Forging N sybils costs N times the stake: linear fake identities demand linear capital, which honest agents split socially but a lone attacker cannot.