Fetch a verified contract's ABI and metadata by address, keylessly, from Sourcify. Returns the ABI plus a summarized list of function and event signatures, the contract name and compiler, and proxy detection (is_proxy + implementation address). Block explorers gate the ABI behind an API key; this does not. Chains: base, ethereum, arbitrum, optimism, polygon, bsc, avalanche. No API keys, no LLM, one x402 USDC micropayment per call.