Thanks GUMS. Got that and agree
But what I was chasing was an interlock to prevent inadvertent selection at some unsafe phase of flight.
Mechanical or electrical doesn't matter provided the selection is possible either a) within design parameters or b) with an explicit procedure that knowingly overrides the protection features
Reports so far indicate that feather unlock was selected outside of design parameters.
Looks like it might have been an oops moment. And sophisticated systems just should not allow oops moments.