If God knows all why did he let Satan into/stay in the garden of Eden?

Or "the serpent" if you don't think it was Satan.

Either way, free will only applied to humans, which means he could have prevented the whole "sin/misery/death" thing by just tossing the reptile out before it ever met Eve.

God knew it would happen, and he just walked off to play Minecraft or whatever, knowing there was a serpent who would Rube-Goldberg humanity into misery.

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