...curl works, wget works

Hmmm, one/both of the above is/are self-evidently not true - look at the error returned from the OS during the rename:

Error while trying to rename '/Users/me/.cpan/sources/authors/01mailrc
+.txt.gz.tmp604' to '/Users/me/.cpan/sources/authors/01mailrc.txt.gz':
+ No such file or directory
[download]

That shouts loudly (to me anyway) that the download of /Users/me/.cpan/sources/authors/01mailrc.txt.gz.tmp604 failed ... quietly.