In this example, of course person A is completely in the wrong, but this is a bigger problem of being so immature that you can't admit any fault.

My suggestion is more along the lines of: use a pairing session for review so that you can bring your empathy as well as your technical expertise, and make it a step in the process just like any other steps (testing, PO approval) etc, and just trust people to do it.

I don't think there's any reason to use a tool from open source, to make code review enforced and with passive aggressive online communication and "blocking". Just seems to make work more painful, and less efficient as well actually.