ContinuousProcesses should not be able to delete particles
It should be considered a bug if ContinuousProcesses delete a particle on the stack. This will remove the particle from subsequent other ContinuousProcesses which is a very complicated and unlogical thing to do.
This is e.g. what happened in #378 (closed) and created wrong LongitudinalProfiles.
At some point we need different "facades" or similar that can change the public interface of "Particles" in different context.