[Xcelerate]

My apologies, I was editing my post while you were replying to it.

> the aggregate system containing both continues evolving unitarily.

The Copenhagen interpretation is that the measured subsystem collapses in a non-unitary way. That doesn't imply the overall system did. I have no opinion* on whether a measured subsystem collapses unitarily or not — the answer to that question does not currently seem to be experimentally testable. But it is testable that the overall system continues evolving unitarily during a subsystem collapse (well, at least up until the overall system is measured), and this has been tested and verified many times.

(* Ok fine, I do have an opinion. I don't think unitarity breaks — ever. I think it appears to break through the process of decoherence. But I'm certainly not going to claim that as fact unless experiment can prove it somehow.)