I know this is unrelated to the issues in !9423 (it's not long), but perhaps we should also consider `TMPDIR`? I've recently seen Unity games attempting to use that, which must be some cross-platform code since that variable is not usually set on Windows. That's lead to issues in some games, since e.g. `/var/tmp` will get converted into `c:\var\tmp`, which will surely not exist in the prefix. For example, the Steam game "Content Warning" (yes, that's its name) ends up showing an error quite often because of this.