The same way that Spotify doesn't just ham-fistedly show you all your Facebook messages... and other apps don't show you messages intended for Spotify. Presuma

The same way that Spotify doesn't just ham-fistedly show you all your Facebook messages... and other apps don't show you messages intended for Spotify. Presumably messages are tagged in such a way that the source and/or destination are intended for Spotify. Using that same system, you should be able to specify "Spotify can only read & write Spotify messages."