nethersx2-turnip-classic documents the shim rules of the revision it
pins, and says so in prose: the classic build is that revision. Compared
to HEAD it reported the same two changes every pass, and recaling would
have repointed its refs at rules this build never had.
pin_frozen says the freeze is deliberate, and the profile is then judged
against its own revision, exactly as one pinned to a superseded tag
already was. Recale and bump are refused for it, which is what makes the
declaration safe to trust.