Name the agent that bought, where there is a signal

Price requests, price checks and the MCP tools now take an optional buyer_agent: a short label naming the buying agent, such as chatgpt or agent.example.com. It is recorded with the quote, lower-cased, and the buyer is recorded as an agent when the request did not say buyer_type. Usage events read it back as buyer_agent. It is a label for learning only: it never reaches the pricing function, so it does not change the price, cached answers or the billed input units.

• Never verified: the name is what the request said about itself. Every recorded agent says verified: false.
• `buyer_agent`: a string of at most 100 characters, or null. A longer value, or anything that is not a string, is rejected with a 400. An identifying-looking value (an email, phone number or IP address) is dropped from the logged quote.
• Store orders: a connected Shopify store's orders keep their sales channel (online store, point of sale, an app's name, and so on). A channel is recorded as a label only, not as proof an agent bought.