The adversary can block a release on its own and cannot unblock one. That asymmetry was deliberate and it is the only reason the role works: an agent that can be argued out of its objection is not a gate, it is a suggestion.
What it catches, roughly in order of frequency: malformed input on paths nobody thought were inputs; state that survives a restart when it should not; and the ugly interaction between a feature written this week and one written eight months ago that nobody remembered.
What it misses, consistently, is taste. It will tell you a flow works. It will not tell you the flow is miserable. That is still someone sitting down with the thing and feeling the friction, and we have not found a way to hand it off — nor are we in a hurry to.