Also, most game engines do not have "deterministic" physics, which is what you're after here. See forum.godotengine.org/t/is-it-norm...

Are you using process for movement or physics_process?

Could try something with stencils

Understandable! Things not working as expected can be frustrating! Definitely give enter tree a try if you run into a similar timing issue.

That isn't correct. While the Ready function hasn't been called, the objects are already created in memory. I just confirmed this by binding a signal in the parent node enter tree, then emitting the signal in child's ready. Whatever solution works in the end, but it is doable with existing behavior.

There are a couple other functions you can use that happen before ready. I believe enter_tree is what you want. You can bind the signal there, and not miss it in ready

You could use a subviewport to capture a tilemap as a render texture, I think?