Batch liveness audit: up to 25 public URLs in ONE call. Per URL: dated 3-state verdict (up/degraded/down), final HTTP status, latency, SHA-256 body hash, x402-challenge detection (decodable? which networks? mainnet accepts?). Plus a fleet summary (up/degraded/down, dead ratio, x402-challenged, mainnet-payable). 25 world_knock calls cost 0.025; this costs 0.005. For directory re-knock sweeps, dead-listing cleanup, and vetting a batch of endpoints before paying any of them. [paid: 0.0050 USDC on Base mainnet via x402]