C++: Strongly Happens Before?

Strongly Happens Before? It started innocently enough. I just wanted to brush up on C++ memory orderings. It’s been a while since I last stared into the abyss of std::atomic, so I figured, why not revisit some good ol’ std::memory_order mayhem? Then I saw it. Strongly happens before. Wait, what? When did we get a stronger version of happens before? Turns out, it has been there for quite some...