Except that Scott did exactly that -- exasperating Buchanan by creating fait accompli regarding the Administration's deliberations over what to do about the forts.
That Scott busted his move at Lincoln's request, given the letter (which indicates previous communication as well) is a no-brainer.
But you're still wriggling, because this shows Lincoln interfering and laying the basis of his war policy.
So you would have us believe. Yet Scott initiated communications with Lincoln in October 1860, as evidenced by this November letter. And apparently continued his communications through November and December, as evidenced by this letter. There is no evidence that Buchanan or Floyd were unaware of the communications. Or that they objected to it. And Lincoln made it clear in his second letter that he relied on Scott to send him only information that he "deem it proper to make to me."
Lincoln didn't go behind Buchanan's back, and he wasn't planning a war. Except in your hyperactive imagination.