Correct, we want to keep the repository accessible during the repack phase with readers not seeing half-written files.

Renaming the old files to temp files is a bad idea. I don't know what possessed me to suggest that to you earlier. Just rename the new temp files onto the real names, if the rename fails because the filesystem won't let you do that, try deleting the real name and then renaming. Yay windows with open files and all that. :-)