[TheOtherHobbes]

So why doesn't a measurement and/or decoherence occur when double slits or a half-silvered mirror interact with a passing particle? Are they not macroscopic objects which interact with the quantum information?

Perhaps it's only a "measurement" if the (alleged) particle has nowhere else to go after the interaction. But how does the (alleged) particle know which macroscopic interactions are terminal and should be counted as "measurements" and which are part of the rest of the experiment?

There is no answer to this in QM. You can calculate the probabilities and you will get predictable answers, but there are still >20 interpretations of what is really happening, and they all disagree with each other in important ways.