x402 payment gate

x402 is an HTTP payment standard. A server can answer 402 Payment Required with an invoice; the client pays, then retries with proof. We use it for paid tool calls.

Flow

1. POST /api/tools/calendar — server returns 402 with invoice_reference and pay endpoint.
2. POST /api/tools/x402/pay with that reference — devnet simulates the on-chain transfer and marks the invoice paid.
3. Client retries the original request with X-Payment-Proof header.
4. Server validates the proof and executes the tool. Receipt lands in /security.

Why MCPay-compatible

We conform to MCPay (github.com/microchipgnu/MCPay) so any MCP-aware agent can pay our gate without custom glue. The invoice format, the pay endpoint, and the retry header are their names, not ours.

What this enables (post-May-15)

Third-party agents can pay us per-call for privileged execution. We can pay third parties for their tools too. The plumbing is the same in both directions.