So essentially, computer A is 'predicting' a (truly random) result from B
Well, the issue I think is within the definitions more than the software, and therefore, this is more philosophical.
ruly Random is impossible for current computer computational process*
For B to make a truly random choice, it would require some form of algorithm to do so, and this algorithm would (by nexcessity) be entirely logical - there may be some possibility in Quantum Computing*? Otherwise, the idea of a Truly Random choice becomes something like that idiom of "An omnipotent Being (God) Creating A Stone so heavy, they cannot lift it". The problem at heat becomes that of a paradox in the definition of "omnipotent" = capable of everything with the word "cannot" = incapable.
Therefore, the rationale of a COMPUTER PROCESS leading to a RANDOM result is the contradiction.
However, given that somehow*, B is able to produce such a result, then A with similar programming technique* to overcome the "sequential incapability to result in a randoim output."
Aside from the potentials of Qubits* I have used, really this whole problem is largely circular. The ONLY means for B to create a random result is through a mysterious and 'impossible' technique C - Given this situation, the ONLY way for A to make any prediction of such, would necessitate A also using at least a similar conceptual technique, also as impossible, as C, let's call it 'D' even though it may be extremely similar to C.
This then destroys the principle determination of the randomnisity, since C is a sequence of instructions resulting in the choice B makes, and D is a set of instructions arriving at a result to equal that of C but for A as the correct prediction.
If it's predictable, it cannot be random. If it's random, it cannot be predicted any better than, as h6ss implies, the actual probability.*So far as current technology and software development goes, For B to arrive at a truly random choice, would necessitate some form of quantum element to computation - by the same token, Quantum computers could identify results from all possible outcomes simultaneously, and produce the most likely such results, so A could use this technique to at least examine the possible results from B.