* Bird is not solid when colliding with other birds.
* If the dev shell is used to run JavaScript during Play Mode, consider
it cheating (so player can't `$ d.Scene.ResetTimer()` for example)
* On Survival Mode levels, DieByFire immediately opens the End Level
(silver score) modal rather than respawn from checkpoint, so levels
don't need checkpoint contraptions to end the level.
* During level loading screens, wait and call doodads' main() function
until the very end.
Noah