We can not be sure how God chose to work..but we do know that God can and will withhold actions that could change the outcome,and by doing that predestinate an event.
Your #1098: God foreknew all the actions of Hitler.God knew exactly what Hitler would do . God allowed Hitler to do as he wanted to do. This non action on the part of God accomplish HIS purposes! Did God predestine the works of Hitler by His non action?
The Calvinist doctrine presented here is that the god they propose predetermined (rather than "allowed") Hitler's actions and inactions, the god's own actions, usually through others (rather than "non action"), and everybody else's actions and inactions, all coming together to determine what would happen. The view is that the god made everything happen that happened, not letting Hitler have a say in any of it (except that he thought he had free will -- an illusion of depravity).
Your idea of the god withholding actions that could change the outcome implies that somebody is making their own free will choices out there that are not predetermined by the god, and that the god has to decide whether to do anything about it.
You had better report for reindoctrination soon. :-) You are not quite toeing the Calvinist line.