Optional Readonlyfinalfinal_gain: the effective final-norm gain γ (stored + 1 of the source's
final norm) the fold moved into lm_head, one per hidden channel. Absent
when the record does not carry it.
ReadonlyhiddenReadonlyr1The residual stream carries the R1 rotation.
ReadonlyseedSeed of R1's sign vector.
What a rotated checkpoint records about its fold.