At some point during code refactoring, we ended up setting up the 3 transition times, intedned
to define when the *previous* transition occured, as we checked to see if a transition
would occur during this ::run() call. This led to (in particular) MIDI clips ending early,
because the transition_beats value was set to the *next* (upcoming) transition, and we used
this to define the timeline position of MIDI events
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