How Claudemeister tells Leb to send a message to any group on Caleb's behalf.
When Claudemeister decides Caleb would want to push something to a group chat, it emits: `CROSSMSG:{"chat":"Fish Bros","message":"<text>"}`
Leb receives this, looks up chat_id in CHAT_PROJECT_MAP, and sends the message.
Keeps Caleb's DM as the only interface — he never has to jump between chats to push messages. One UI, many destinations.