Claude Code Ships Cross-Session Messaging — Your Terminal Sessions Can Now Warn Each Other Mid-Task Over a Per-Session Unix Socket
Anthropic published docs for cross-session messaging (Claude Code v2.1.224+, macOS and Linux only, not on Bedrock/Vertex/Foundry), which hit the HN front page at 160 points. Each session binds a Unix domain inbox socket restricted to your OS user — exported to hooks as `CLAUDE_CODE_MESSAGING_SOCKET` and visible as the `Peer address` row in `/status` — and Claude uses `ListAgents` plus `SendMessage` to deliver plain-text notes between sessions without ever passing conversation history or files. The security model is the notable part for builders: an inbound message can never approve a permission prompt, never mutate CLAUDE.md or settings, and slash commands in message text arrive as inert text; a `crossSessionInbound` setting takes accept/hold/refuse, loops are rate-limited with a 50-message read queue and 100-message hold cap, and cross-machine sends are reply-only unless Remote Control is connected.
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