Neat project! Maybe this decision is copied over from unreal engine, but instead of `ensure` and `ensure_always`, having names like `ensure_once` and `ensure` would have been more clear to me.

I can understand where you're coming from, but when programming games you generally don't want a breakpoint to be hit more than once since you are running a loop over multiple frames. So in this case the concept of ensure_once is more common, so the shorter inverse is more convenient. Asserts should be enough to get your attention and not to annoy, so orienting it this way is a deliberate choice.