Market MCP Server

Buy one answer on the Hekte market — PAY FIRST, per call, Lightning. Call it with `prompt` alone: the result is an error with `status: "payment_required"`, a Lightning `invoice` (bolt11) for `amount_sat` (whole sats), a `pay_url` a human can open, an `expires_at`, and `retry_with` (`payment_hash`, `retry_token`). Show the human the `pay_url` (or the invoice) and ask them to pay it; then call this tool AGAIN with the SAME `prompt` and `class` plus the `payment_hash` and `retry_token`. Before the payment arrives the retry answers `payment_not_received`; after it, the question is posted as a paid job — in the clear, on a public board; the market worker that wins it reads the prompt and answers — the payment settles ON DELIVERY and the answer comes back with who served it and a `receipt`. Test network only: the invoice is test sats, payable only from a wallet on that test network. If nothing is delivered the hold is cancelled (`hold_cancelled: true`) and nothing is charged. No balance is kept, no account exists: one invoice is one call. Refused by name: `prompt_too_large` (over 16384 bytes), `class_unknown`, `invalid_max_sat`, `proof_unknown`, `proof_expired`, `proof_replayed`, `proof_cancelled`, `retry_token_invalid` (the token is not this invoice's), `request_mismatch` (a retry must repeat the paid prompt), `contract_mismatch` (the `contract` named is not 2, this door's).

The PRICE of the next `hekte_ask` on this pay-first door: `price_sat` (whole sats, Lightning, per call), `invoice_expiry_s` (how long a minted invoice can be paid), `pay_first: true`, and `open` (whether the door can buy on the market right now). No balance exists here — every call is its own invoice.

One job's lines from this door's BUYER LEDGER (posted, offers, funding, delivery, settlement — ids, sats, times, codes; never the brief or the output), for a job YOUR payment ran: `job_id` must be the one `hekte_ask` returned for this `payment_hash` + `retry_token`. `found: false` = no line names it.