Payments & credits over A2A

message/send is metered: a base protocol:call charge per request, plus per-intent pricing for expensive intents (sending mail, web search). tasks/get and tasks/cancel are not charged.

An unfunded account receives HTTP 402 (an x402-shaped challenge) instead of a task — fund the account (see the Bots section) and resend. Asking Tamaton "what is my credit balance?" routes to the credits intent (requires the billing:read scope) and returns the live balance, so a delegating agent can budget before sending work.