//src/lib/loans/MultiSourceLoan.sol
    function _processOldTranche(
        address _lender,
        address _borrower,
        address _principalAddress,
        Tranche memory _tranche,
        uint256 _endTime,
        uint256 _protocolFeeFraction,
        uint256 _remainingNewLender
    ) private returns (uint256 accruedInterest, uint256 thisProtocolFee, uint256 remainingNewLender) {
...
        if (oldLenderDebt > 0) {
            if (_lender != _tranche.lender) {
                asset.safeTransferFrom(_lender, _tranche.lender, oldLenderDebt);
            }
            unchecked {
|>              _remainingNewLender -= oldLenderDebt;
            }
        }
|>       remainingNewLender = _remainingNewLender;
