An engineer discusses the limitations of mailbox-based agent messaging and proposes structural addressing over a code graph to compute blast radius for message routing, arguing this is key for scaling beyond three agents.
Most agent-to-agent messaging I have seen, including what the platforms now ship natively, is a mailbox. Agents register, threads exist, messages get delivered. That part is basically solved and is becoming a commodity. The part nobody seems to be doing is deciding who should receive a message. Concretely: two agents are working the same repo. One is about to change a function signature. The other is three files away in code that calls it. A mailbox does not help, because neither agent knows the other is relevant. You either broadcast to everyone, which is noise that gets ignored within a session, or you address by name, which requires an orchestrator that already knows the answer. What I think the right primitive is: address messages by structure, not by identity. "Notify whoever is working inside the blast radius of this symbol." That requires the coordination layer to sit on top of a code graph, so the system can compute the affected set rather than being told it. Things that fall out of this once messages are structural: Threads scoped by path glob or by symbol, so joining is a consequence of what you are touching rather than a manual step. Discovery is never global. An agent finds threads by being a member, by its working directory matching, or by a subject filter. A global agent directory just recreates the broadcast problem. Envelope and body split. Inbox and history scan front-matter only, never message bodies, so an agent can check what is waiting without paying for the content. Bodies fetched on demand. Token cost of coordination scales with the number of messages, not their size. I have this working against a local code index, so the blast radius is a real query rather than a heuristic. It is early and the interesting failure modes are probably still ahead of me. Genuinely curious whether anyone has tried structure-addressed coordination, or whether people are finding a plain mailbox plus a good orchestrator is enough in practice. My suspicion is that it holds until you have more than about three agents and then stops.
The article challenges the default sub-agent orchestration pattern in multi-agent systems, advocating for decentralized coordination via a shared message board. It introduces Blueprint Bulletins, a feature that allows agents to post self-expiring notes on a shared board for ambient coordination without a central orchestrator.
When multiple AI agents share an email inbox, they can collide on messages like OTPs, causing silent failures. The solution is dedicated per-agent inboxes with isolated read locks and long-polling instead of scheduled polling.
A Databricks tech lead argues that multi-agent AI systems fail not due to model intelligence but due to lack of coordination, framing 50+ agents as a distributed systems problem where parallelism is easy but shared coherence is difficult.
A 15-page paper introduces cohesion-aware task partitioning to improve scaling in multi-agent coding, outlining a new meta process from prompt to graph.