If the provider's sidebar is closed but their worker notices a new chat message, the worker should be able to arrange for a service (chat) window to be opened. critical, but not a blocker, as Amigo would like it sooner rather than later :)
it would have to be limited to only the current provider. As well, there are abuse scenarios here, especially while the service window is a top level window. It would be better to see the status indicators in the toolbar update to let the user know a chat request has been made, let the user open the chat.
there is a thread on the email list about this, it seems to be leaning towards not allowing the worker to open any windows, and relying on status icons/panels. We need a quick decision.
notifications in bug 774506 provides a mechanism for the worker to let the user respond to chat requests