Ask before closing a proof whose branches are "used" in other proofs

[unp1]

Please describe your proposal in a ONE sentence

Removing a proof might unexpectedly reopen branches on other proofs

Underlying problem

Removing a proof that is referred to by other proofs causes branches on the other proofs to be reopened

Usage Scenario

When removing a proof via Cmd + W (Ctrl + W) or "Abandon Proof", we should check whether the proof is referred to by branches of other proofs and provide the option to first "copy" the cached branches to the other proofs.

[WolframPfeifer]

While it is still a valid feature request to ask for the user choice individually, I just wanted to mention here that there is actually an option under "Options" -> "Show Settings" -> "Proof Caching" to change the behavior:

The default should be "Copy referenced steps", but it seems that in your case it somehow got changed to "Reopen" ...