COMMUNICATION AND PROTOCOLS BETWEEN AGENTS

CHAPTER SUMMARY Agents can communicate through a message bus using publish and subscribe, or through a graph of nodes and edges that defines allowed paths. Buses give loose coupling and a natural log, and graphs make allowed paths explicit. Agent-to-agent standards, such as the Agent2Agent protocol, complement MCP and let independently built agents cooperate, but messages from other agents must still be treated as untrusted. Deadlocks and runaway loops are avoided with clear termination conditions, limits, timeouts, cycle detection, escalation to a human, and designs without circular waiting. A meta-harness provides shared budgets, permissions, logging, policy, and kill switches across many agents. KEY TERMS REVIEW Message bus: a shared channel agents publish to and subscribe from. Publish and subscribe: sending messages by type and receiving only the types you chose. Coupling: how tightly two parts depend on each other. Graph, node, edge: points connected by lines that define allowed paths. Agent-to-agent standard: an agreed format for independent agents to cooperate. Agent2Agent (A2A): a protocol for agents to talk to other agents. MCP: an open standard connecting agents to tools and data. Deadlock: parties waiting on each other forever. Livelock: busy but making no progress. Timeout: a maximum wait time. Meta-harness: a system combining and controlling many agents.