The Agent Handoff

This paper examines the least-governed boundary in modern multi-agent AI systems: the agent-to-agent handoff. While interoperability protocols such as Model Context Protocol (MCP) and Agent2Agent (A2A) successfully standardize communication between autonomous agents, they do not determine whether delegated authority remains valid at the moment of execution. As a result, orchestration failures increasingly arise not from model reasoning errors but from stale or revoked authority crossing agent boundaries. Building upon the Constitutional AI Governance Runtime developed in the author's governance series, the paper introduces the application of Handoff Validity, Execution Fidelity, Portable Authority Boundaries, and Delegation Chain validation to agent-to-agent delegation. Rather than proposing a new protocol, it demonstrates how existing interoperability standards can be extended with runtime governance metadata that enables receiving agents to independently re-establish execution legitimacy before accepting delegated work. The paper distinguishes identity, delegated authority, and execution standing as separate governance properties and argues that interoperability alone cannot guarantee legitimate execution. It further discusses implementation considerations including freshness validation, replay protection, authority propagation, delegation chain compaction, and consequence-aware runtime verification while identifying remaining open research challenges such as cross-organizational audit, distributed registry consistency, and multi-principal agent deliberation. The work contributes a practical governance extension for multi-agent AI ecosystems that complements existing interoperability standards without modifying their transport semantics, positioning runtime admissibility verification as a foundational requirement for trustworthy autonomous agent collaboration.