Variable A2A_X402_EXTENSION_URI`Const`

A2A_X402_EXTENSION_URI: "https://github.com/google-agentic-commerce/a2a-x402/blob/main/spec/v0.2" = 'https://github.com/google-agentic-commerce/a2a-x402/blob/main/spec/v0.2'

Official a2a-x402 extension URI (x402 v2 A2A transport). Declaring it tells generic A2A clients this agent speaks the standards-compliant in-band x402 flow (payment signalled through Task / Message x402.payment.* metadata).