Well, good. Your problem is artificial, choosing tools and scenarios to avoid "push". Your problem isn't with invalidating caches being hard in 2025. I've explained how to do it in both pull and push scenarios. Certainly not "the only hard problems in computer science." And neither is naming!

I’m also not making my own programming language, I’m using PHP. And I’m using MySQL. What is your point?

Are you saying that “invalidating caches is hard… if you insist on using only systems with no way to push updates, and oh if they have a way to push updates then you’re using someone’s library to consume updates so it doesn’t count?”