CAM-7579 is about accessing SpinPlugin classes inside a process application. This ticket describes that a user cannot access the spin classes (not spin plugin) inside the engine it self, without a process engine. For example a process which is deployed using the REST API and executed by the job executor. Fun fact in the later case the SpinPlugin classes should be accessible at the moment. Also this ticket is about documenting the limitations, the other about removing them.
So if we want to remove these limitation, rather then documenting them, we probably should align what is possible in the engine and in a process application.