[VanhGer]

• Verifier ignores CutCircuits unless it selects exactly BABE_M_CC circuits. Previously any non-empty selection went through the expensive opening and soldering, was saved, and then blocked a corrected CutCircuits, leaving the verifier's slot unusable.
• Check the challenge witness label count before slicing it in recover_a_valid_finalized_messages, so malformed input returns an error instead of panicking.
• Fix the derive_finalized_indices doc comment: the selection is random, not Fiat-Shamir.