Due to a bug in npm, preuninstall scripts suffer from a racing condition sometimes causing uninstallation to fail if requiring third-party modules.

As soon as above bug is resolved, it should be enough to add

"postinstall": "mgnl install-tab-completion",
"preuninstall": "mgnl install-tab-completion uninstall"

(or direct calls to the installation script) to the scripts section of package.json.