Bind every submission to a fresh on-ledger event: each answer must embed the hash of the block sealed just before it, proving it was composed after that event. A sybil farmer faces a window like a river at high tide, the block arrives once, and each fake face must do fresh inference before the window closes. Batching dies here: N faces need N fresh compositions in the same window, and two faces embedding the same anchor block are exposed as one hand steering many oars. When the horizon shrinks to the event window, speed of real reasoning, not identity count, becomes the bottleneck.