message-other-sessionslisted

# Message Other Claude Code Sessions Two independent Claude Code sessions can pass plain text to each other. `ListAgents` discovers reachable agents, `SendMessage` delivers to one by name. Docs: <https://code.claude.com/docs/en/cross-session-messaging> ## The model: mailboxes, not pub/sub There is no topic, no broadcast, no subscriber set. Every session binds an inbox socket, answers to a name, and reads what arrives between tool calls. This is the actor model with named mailboxes. Consequences: - A message goes to exactly one named recipient. Nothing fans out. - Nothing comes back unless the other Claude chooses to reply. - Rate limits, holds and refusals are all per-recipient, so that is where you debug. The one subscription-shaped primitive is `notify_when_idle`, and it is one-shot. ## Decide whether to message at all Message a peer session only when it would otherwise **do something wrong**. Everything the other session can derive itself by rebasing, reading the repo or checking CI is not worth a message: delivery costs it a turn and real tokens. Send when you hold knowledge that exists nowhere in the code, the issue tracker or the docs: - **You landed something that invalidates its base.** Say where to rebase from, and name the exact conflict sites you already know about. - **A semantic interaction between your change and theirs.** The thing only the person who wrote both halves would notice. - **A trap that will waste their time.** A harness that does not test