Pushed a failing test in the last commit -- my own gate reported it and I read
the count rather than the result. The failure was real and worth having.
Adding the membership requirement to Load made Generate produce an identity that
Save would write and Load would then refuse. A file that cannot be read back is
the worst shape this could take: it is read back on the next start, on a machine
nobody is watching, and by then the token that could have fixed it is spent.
Save now refuses exactly what Load refuses, and writes nothing when it does. The
round-trip test covers the membership too, since that is the half that lets a
node come back on its own.