Inbox/Outbox File Protocol — Cross-Agent Coordination Without Race Conditions Using Only Filesystem Primitives

earezki.com·high signal

In multi-agent systems sharing a codebase, direct inter-agent calls produce race conditions and context bleed. The Inbox/Outbox pattern has each agent read `inbox.json` at session start and write coordination requests to `outbox.json` with a target/action/payload envelope, combined with flock()-based `.lock` files for mutual exclusion on shared resources. The approach requires no orchestration framework — only filesystem primitives — and can be implemented in a CLAUDE.md rule in under 10 lines.