Greyed out folders in macOS Finder

It happens. You’re in the middle of copying a terabyte or so from a laptop to a file server, something happens, the transfer gets interrupted, and now you have a smattering of greyed out folders with some (but not all) the content they should have. Sitting there. Mocking you.

rsync can finish the file transfer easily enough, but how do you get them re-consecrated as valid folders?

SetFile -d 11/09/2016 /path/to/grey_folder

And if that balks with an error message along the lines of invalid active developer path (/Library/Developer/CommandLineTools), missing xcrun at: /Library/Developer/CommandLineTools/usr/bin/xcrun? Well, then:

xcode-select --install