* `edit.update(state, dt)` -- call this from `App.update` to periodically
  auto-save editor contents to disk.

* `edit.update(state, dt)` -- call this from `App.update` to periodically
  auto-save editor contents to disk.
* `edit.quit(state)` -- call this from `App.quit` to ensure any final edits
  get saved before quitting.