code: func (pm *PermanodeMeta) restoreInvariants(signers signerFromBlobrefMap) error {
  	sort.Sort(camtypes.ClaimPtrsByDate(pm.Claims))
  	pm.attr = make(attrValues)
  	pm.signer = make(map[string]attrValues)
  	for _, cl := range pm.Claims {
  		if err := pm.appendAttrClaim(cl, signers); err != nil {
  			return err
  		}
  	}
  	return nil
  }
docs: // restoreInvariants sorts claims by date and
  // recalculates latest attributes.