Most protocol diagrams put  Model Context Protocol (MCP), Agent2Agent (A2A) protocol, and Agent Communication Protocol (ACP) in three equal columns. I think that framing causes half the confusion. They aren't three interchangeable ways for agents to chat.MCP solves a capability-access problem. A2A solves a delegation problem. ACP explored a REST-first version of agent communication. Once those boundaries are separated, the architecture becomes much easier to reason about.