Agents can report "the buyer accepted" without looking up an id

Reporting whether a price was used is what learned pricing learns from, and it now takes one argument. After compute_price, an agent that hears the buyer accepted or turned the price down can call report_outcome with just outcome.

• Works on the local (stdio) MCP server and in the tools packages for LangChain, the AI SDK and the Agents SDK (reportLastOutcome and lastUsageEventId on the client). A completed pricing_conversation counts as the last price too.
• In the tools packages the memory belongs to the client behind the tools. If one server answers many buyers' conversations, use a client per conversation or pass the id. Any pricing_conversation call that does not complete forgets the previous price.
• The remembered price is reported once. A second report without an id is refused, so an outcome never lands on the wrong price twice.
• A failed compute_price forgets the previous price, and an answer from the public demo is never remembered.
• Pass usage_event_id whenever you priced more than one thing. The hosted endpoint remembers nothing between calls, so it still needs the id.