Structured Data Extraction API — URL to typed JSON (schema extract, keyless x402)

TYPED structured extract for autonomous agents — URL + schema → a clean, type-safe JSON record. Where /buy/fetch returns page TEXT (and ?extract= returns string-only fields), THIS returns the schema-conformant object an LLM/RAG/trading pipeline actually consumes: pass ?url=…&schema=title,price:number,rating:number,inStock:boolean and get back { title:"…", price:19.99, rating:4.5, inStock:true } — numbers as numbers, booleans as booleans, absent fields null (honest). schema accepts the URL-friendly compact form (field[:type], type in string|number|integer|boolean) OR a Firecrawl/OpenAI-style JSON-Schema object ({"properties":{"price":{"type":"number"}}}). That is Firecrawl's paid 'JSON mode' headline guarantee — type-safety, 'numbers as numbers not strings' — done DETERMINISTICALLY from the page's own JSON-LD/OpenGraph/meta/microdata: keyless, NO LLM call, NO API key, NO signup, $0.004/call, paid in-band over HTTP 402 (x402, USDC on Base mainnet). The typed record is folded into the SIGNED provenance attestation too (EIP-191, ecrecoverable OFFLINE), so a buyer can prove the EXTRACTED FIELDS — not just raw bytes — are exactly what MERCURY resolved. Honest charge-per-ATTEMPT: every call returns a structured result (success OR an ok:false reason). Same SSRF guard, 5s timeout, 10MB cap, no mint.