Every multi-agent system is, underneath, a machine for handing work from one context to another. The handoff — how state, intent, and authority transfer — is where multi-agent systems quietly succeed or systematically fail.

A handoff loses information in three characteristic ways. Compression loss: the sender summarizes and the summary drops a constraint that mattered. Assumption loss:the sender's implicit knowledge — what was tried, what was ruled out and why — never makes it into the packet. Authority ambiguity: the receiver does not know what decisions it may make, so it either stalls or freelances. Classic telecommunication solved the first with structured protocols; the other two are why aviation adopted the readback — receivers repeat the instruction back before acting.

The engineering answer is the handoff contract: a typed envelope containing the objective and its success criteria, the relevant state and artifacts with pointers, constraints and non-goals, the decisions already made — with reasons — and the authority boundary: what the receiver may decide alone, must escalate, and may not touch at all. Note what is deliberately excluded: the sender's raw transcript, self-assessments, and confidence. A handoff is a fresh start with carried conclusions, not a context dump with a greeting.

Handoff Hygiene

• Acknowledge by readback: the receiver restates objective, constraints and authority in its own words before starting; mismatches surface in seconds instead of after the work.
• Idempotent acceptance: a retried handoff must not double-start work — the envelope carries a unique task ID the receiver deduplicates on.
• Bounded rehandoffs: a task bounced between agents N times is mis-specified; the loop breaker is to escalate to the human who owns the ambiguity.
• Version the contract: as the fleet evolves, envelope schemas evolve — old receivers must fail loudly on unknown contracts, not improvise.

The blunt summary from every team that has operated a fleet: agents are rarely the bottleneck — interfaces are. Design the handoff first, the agents second, and the multi-agent hype writes its own ticket.