Note that Orkos, the well-known supplier for instinctive eaters in France, sells shelled cashews that are apparently truly raw. They are devitalized. The American chestnut is no longer of commercial importance. They may spoil quickly after harvest, so should be refrigerated or frozen for storage. Chestnuts are usually sold in-shell.
Processing varies somewhat by variety.
Chinese chestnuts are cured by spreading them on a floor, stirring frequently, and waiting 5-10 days. They are then cured for 1-2 days in a manner similar to Chinese chestnuts. If the nut shell is watertight, the water will not be absorbed. Slitting the nut shell allows water to get in, but the most noticeable effect is to sharpen the astringent flavor of the skin of the nut, making peeling absolutely mandatory. Note that unsoaked, raw peeled nuts have a very sweet, agreeable flavor.