I learned today that when copying files from readonly media (ie, a CD) to a read-write device, the files are copied with the write bit turned off. So the files are just as useful for editing as they were on the CD.
chmod +w -R . worked to fix this: I gather there’s some Windows right-click property munging I could have done, but the same guys invented that as created the problem. I’d just as soon not ask them for more help.