Your wonderful essay contains a flaw.
"box B contains the diamond"
There is no way in reality to check correctness of reasoning result "directly" (unable to "open box and see if it contains brilliant"). But, if result of reasoning is not directly influences the reasoner, it is also unfeasible .
So, correct story is: "one of two melted unopenable boxes contains bomb with timer. The task is select one box and throw in deep well, or else it shall explode and mutilate the reasoner"