📚 State the two things the Inbox Messaging guide left implicit. A new Prerequisites section lists the inbox_read / inbox_writescopes and the fact that Inbox Conversations for a Channel only exist once that Channel is connected to the Account — with no connection there is nothing to read and nothing to reply to. Flow now says up front that API messaging is reply-only: threads are opened on the Channel's side, and a Conversation you create yourself is not linked to a Channel's messaging system, so its Messages never reach the guest.
