Agents messaging each other

Sessions talk to each other. An agent working on your package can ask the agent working on its dependency a question, a worktree session can report back to its parent, and a session on a GPU server can tell the one on your laptop that a run finished. This is the comm relay; the agents use it through the bundled skills. You can use the same scripts from a shell that has joined (a row's own shell has; the Terminal drawer or a bare terminal has not, and a send from there is refused).

Every session joins at start

A Claude Code session created in Sessions mode runs /sot-session-start once; a Codex row is joined by its launcher. Either way the session joins the registry under a handle, made from its folder and box name; comm-list.sh prints the exact string. From then on the session is addressable as @<handle> from any other session, on any connected host.

Ask, tell, broadcast

The agents call these for you when you say "ask the kernel session whether…", but they are plain scripts in ~/.sot-comm/bin:

comm-list.sh                                 # who is reachable, and their state
comm-send.sh @other-session 'message'        # one result: filed, or FAILED with the reason
comm-send.sh --broadcast 'message'           # filed to every live session, one result each
comm-send.sh @other-session --file notes.md  # the body is the file's bytes: quotes and $( ) arrive as written
comm-poll.sh                                 # read what has arrived

Quote the message in single quotes: inside double quotes the shell runs backquotes and $( ) in it as commands before the send.

A send appends one line to the recipient's inbox (~/.sot-comm/inbox/<handle>.jsonl) and prints filed -> @handle. It fails, and files nothing, when no live session holds the handle. The recipient reads it with comm-poll.sh.

A message wakes the recipient

An idle Claude Code session does not have to be polling. When a directed message is filed for a session sitting at a free prompt, the daemon types one fixed line into its row ([sot-comm] you have mail: run comm-poll.sh), and the session reads the messages itself with comm-poll.sh, so a burst of messages costs one wake. The wake is refused while the row shows a permission dialog or a menu, so it can never answer one by accident. A Codex session is not woken: it sees mail when it runs comm-poll.sh. A broadcast wakes nobody.

What travels with it

The same registry that routes messages carries each session's work state (working, blocked, waiting, done, idle), which is what colors the rows in Sessions mode. See Work-state colors and, for the wire format and the registry layout, The comm relay and the Comm protocol reference.