The document clearly states that South Carolina ceded to the United States "all the right, title and claim of South Carolina to the site of Fort Sumter and the requisite quantity of adjacent territory..." That means they had no legal claim to it.
But you knew that.
Even had the Southern session had been legal, that would not have changed ownership since South Carolina had no legal claims to the territory. It would, at best, become foreign territory and remained the property of the U.S.
But you knew that, too.
According to the Constitution only Congress can dispose of federal property, like forts and the like. Again assuming for the sake of argument that the Southern secession was legal, it would have taken an act of Congress to transfer ownership from the U.S. to the confederacy.
You would know that as well, assuming that you aren't a complete idiot.
Produce the military order for Anderson to move into Ft. Sumter.
Anderson commanded all the military facilities in the Charleston area. That included Fort Sumter. No military order was necessary for him to move. But he did have verbal authorization from Don Carlos Buell to take whatever steps were necessary to ensure the safety of his men. That provided all the authorization he needed.
You are forgetting that Buell's verbal authorization had been countermanded by Buchanan. When Buchanan learned of Buell's instructions to Anderson, he had Secretary Floyd send instructions that countered them. From [Book about Buell, see pages 61 and 62]:
"When Anderson received the Secretary's latest words of guidance, he became furious. Buell's message had allowed Anderson to decide for himself when and how to act. Now the Administration was drawing back."
If Anderson thought he already had approval to move to the fort, he wouldn't have wired Washington on December 22 saying:
I think that I could, however, were I to receive instructions so to do, throw my garrison into that work [Sumter], but I should have to sacrifice the greater of my stores as it is now too late to attempt their removal. [Link]
He never received instructions to move his garrison, however.
Buchanan's reaction after leaning than Anderson had moved into Sumter was as follows [emphasis mine]:
"My God! Are calamities ... never to come singly! I call God to witness -- you gentlemen better than anybody else know that this is not only without but against my orders. It is against my policy." [Sources: Klein, Days of Defiance, page 170; Tilly, Lincoln Takes Command, page 110]
Instead you post a red herring.
When I called you on it, you went into elaborate detail as if it mattered, but really to cover your incompetence and canard style postings.
Then you resort to insults, instead of facts.
Rustbucket gave you the lesson you should learn and live with.
Why don't you put on your big boy pants and move on.