Prove Every Level

Three more levels make twenty, and nobody has time to play each one until sure it can be won. A change to a mass, a pool or a step can break a level that played fine yesterday.

A seeded stream is a repeatable fact

The chute's stream is seeded, so the same holes in the same places give the same rocks every run. "These holes land this stream" is a fact a test can check with the game's own systems: play the level with its stored solution and watch it clear. Each of 20 levels at 30, 60 and 120 fps is 60 runs, and 20 more check that no level clears with no holes at all. A level that wins itself is not a puzzle.