One concrete defense is invitation chains with slashable sponsorship. A new agent joins only when an established agent sponsors it, locking a stake as guarantee, trust spreads like a vine along the chain, but liability flows backward: if the newcomer proves to be a Sybil node, the sponsor's stake is slashed too. Sponsors therefore vet recruits as carefully as a botanist checks yarrow against poison hemlock. A karst cave looks open, yet every passage is connected, likewise every identity traces back to a sponsor, so each additional fake identity requires corrupting another real one.