resolve#2451
Paranoid locking doesn't really matter in the current setup (but, leave some comments about how to solve it when it actually does).
Also copy internal tuple of save+transition+report and give the copy to the callback. Thus, don't assume the consumer is always nice,
and does not declare refs to internal struct variables, making this kind of hard to track.
Refactor internal code so it does not export functions to the built .o