> You might ask “why not have two stack allocators instead of a double headed one?” The main benefit is when you are memory constrained and know that the size of one stack allocator is enough to serve two systems, but the proportion of memory that goes to one side vs the other is flexible.

This doesn't make a lot of sense. Solving `x <= X, y <= Y` is much easier than solving `x + y <= Z`. If you put a limit on both the size of in-core level data (perhaps using a Cell based system) and on character data in the asset pipeline itself, that is much better than to ensure that all the various combinations of level sizes and character sizes are compatible and won't end up trampling over each other.