Keep in mind, I am the one here going by what the Constitution actually says - not by what you wish it said.
Again, the Treasury Department is under the authority of the President, not the Congress. But if you insist that the Treasury Department is some sort of Executive adjunct of the Legislative Branch, then by all means show me where in the Constitution that power is derived. "Living Constitution"? Please. There is nothing more Conservative than placing limits on Government which is what our Constitution does. Except for some unknown reason, you wish to remove one of those limits to give Congress Executive authority. Bah! To hell with that.
You continue to ignore the fact that there are four branches of government. And that the powers of both the Executive and Legislative Branches are derived from the fourth.
Want another example? How about the EPA. The EPA (allegedly) runs a superfund that accumulates money from year to year. But how can that be? According to you, Congress ordered the EPA to spend the money. Yet the money accumulates unspent at the direction of the Executive Branch. Is it possible that Executive Power is vested to the President and not to Congress? Our Constitution certainly thinks so.
The problem here is that you simply don't like the fact that the President does not have to spend money that Congress appropriates because you fear that it could cost you somewhere down the line. But that is the government we have. Congress doesn't like it either which is why they enacted a law to circumvent it. If it was truly Constitutional for the Executive Branch to be a patsy of Congress, then Congress wouldn't have felt compelled to pass that law increasing their power. But they did. Which proves that even Congress recognizes the Constitutional authority of the Executive Branch.
But for the sake of argument, let's see your fear scenario through to the end. Let's say that the President decides to clean up the food stamp program. Throughout a fiscal year, the Executive Branch determines that half the people collecting food stamps did not qualify. So it chooses not to hand that food stamp money out, leaving a surplus of funds at the end of the fiscal year. According to you, the President is in violation of the Constitution in doing so since you insist that the President MUST spend money that Congress has appropriated. So let's examine the Constitutional courses of action here. Congress can use its power of the purse to extort the President into reversing course. Or someone can sue leaving it up to nine black-robed tyrants who may or may not rule based on the Constitution. Or the fourth branch of government may step in and remove Congress, the President, or both. This is the Constitutional government we have, like it or not. And there is NOTHING in that Constitution that compels the President to spend money that Congress appropriates. Nothing.