-
Today's basic Godot revelation: You can set a node's groups in the editor. Before I thought metadata had the advantage of being available in the editor, while groups make nodes accessible to handy methods like `tree.get_nodes_in_group()`. Now that metadata advantage is gone. (It still has the advantage of being able to be types other than boolean.)
With that, I've been able to get rid of a lot of `_ready()` implementations that were all group-setting.