The schedule that contains logic that must run after Update. For example, synchronizing “local transforms” in a hierarchy
to “global” absolute transforms. This enables the PostUpdate transform-sync system to react to “local transform” changes in
Update without the Update systems needing to know about (or add scheduler dependencies for) the “global transform sync system”.
The schedule that contains logic that must run before Update. For example, a system that reads raw keyboard
input OS events into an Events resource. This enables systems in Update to consume the events from the Events
resource without actually knowing about (or taking a direct scheduler dependency on) the “os-level keyboard event system”.
An event that indicates the App should exit. If one or more of these are present at the end of an update,
the runner will end and (maybe) return control to the caller.