How does one handle an upgrade to mutators? If a client is running old code then the operation will differ to the server. Obvious answer would be to version them independently: `increment_v1`, `increment_v2`, but wondering if there is a better answer?
At the moment there is no better answer than do not remove your old mutators until you know there are no more clients out there that might have pending changes.
Right now that window is pretty small because we haven't turned on persistence yet.
