While there are only 8 questions tagged with stack, it might make sense to separate protocol stack questions from activation record stack (or more generally stack as as software data structure) and from evaluation stack (which could use a tag text like 'stack-processor' even though it would apply to the Java VM and probably to x87).
So would it be appropriate to retag the protocol stack questions with a new tag protocol-stack and use stack for the software data structure (including activation record stack) perhaps with a note in the info text/tag wiki summary that questions about evaluation stacks (if any are ever asked) would be tagged stack-processor?
In hindsight, perhaps protocol stack questions might be moved to protocol.