In process of completely revising the collision engine.
It’s a simplified physics model, much like sliding-block physics of, say, Pengo from the 80’s. All colliders are axis-aligned boxes. Pushes can be transitive. And each movement has a force associated with it, which determines how much it can push, or if a wall will stop it.
The first version was prone to silly troubles like allowing penetration of side walls in some tight corridors. A future blog post shall give excruciating detail!