So you can show me this contract in the Governmentwide Point of Entry, as is required under FAR Part 5?
No, you can't. You can try to escape the substance of the argument with phrases like "semantic-smith" if you'd like, but law is semantics.
And no, the judges referencing the memo that claims such an agreement exists does not indicate that judges "buy it" that there is a contract. The case before them is not about contracting compliance and public records, so they wouldn't be interested to bottom out that issue. The quoted language is not even allegedly from any agreement, contract or not, formal or informal. The quoted language is from a memo about the alleged agreement.
Edit to your edit:
> they aren't buying your case that informal arrangements are nothing but memos.
Ah, so it's "an informal arrangement" now? Interesting change of heart you've had. Our government is not allowed to make "informal arrangements" that involve shipping human beings to foreign governments and paying them several million dollars per year, for all sorts of very obvious procurement and budgetary reasons, even aside from the human rights issues.