If it isn’t umask, I don’t know what the reason is for the files missing permissions, whether it is something that zig does explicitly or whether it is a bug.
Maybe you could do something like here, until you find out the reason?:
Maybe another reason would be that the user that executes zig fetch doesn’t have the permissions to create a file with those permissions? So basically I mean, maybe there are other things besides umask that can interfere with the resulting permissions? (My knowledge is limited in this area, but I think something like this could be the case)