Thanks, I had Claude walk me through the code if anyone is curious:

https://claude.ai/share/12357895-d585-4475-93fb-cdb5eba5dd76

tl;dr It's not an implicit animation framework like Core Animation or CSS animations. Instead, each frame you get the current value which is then used, and the actual tween curve only changes when you call a tween function with a new target; otherwise, you get the current (tweened) value since the last time the target changed (which might be the final value).