Lock app
It would be a nice feature to be able to lock the app without logging out. As we can only deliver and receive messages while the app is running, one might be tempted to leave it running while leaving the desk. Of course, one should use the screensaver lock or whatever mechanism to protect others from using anything on one's machine at all (remember, don't leave any root shells open ;)), as briar is an app that most likely contains sensitive information, it would be nice to have a lock feature of its own.