Since moonup can already be used to upgrade the toolchain, through the moonup update command. It should be good to intercept moon upgrade and proxy to moonup update to do the job of upgrading the toochain.

Running moon upgrade directly can break the shims created by moonup and eventually break the whole moonup installation. By implementing the interception, the problem can be avoided.

moonup update only upgrade the latest toolchain, which I believe should already matches the behavoir of moon upgrade, the interception should be implemented in moonup-shim.