When one of your sessions learns something another session needs, such as a finding, a status, or a decision, Claude passes it along instead of you copy-pasting between terminals. Claude discovers the target with ListAgents and sends with SendMessage, so you never call either tool yourself. Claude can decide to send a message without being asked, and you can also prompt for one.
Message your other Claude Code sessions - Claude Code Docs
I’ve had a hard time decomposing some tasks into multiple agents because of this kind of knowledge flow. Looking forward to testing it out.