code: func (pm *PermanodeMeta) fixupLastClaim(signers signerFromBlobrefMap) error {
  	if pm.attr != nil {
  		n := len(pm.Claims)
  		if n < 2 || camtypes.ClaimPtrsByDate(pm.Claims).Less(n-2, n-1) {
  			// already sorted, update Attrs from new Claim
  			return pm.appendAttrClaim(pm.Claims[n-1], signers)
  		}
  	}
  	return pm.restoreInvariants(signers)
  }
docs: // fixupLastClaim fixes invariants on the assumption
  // that the all but the last element in Claims are sorted by date
  // and the last element is the only one not yet included in Attrs.