I know that some containers craft.  Setting that aside, when a player is crafting something from the personal crafting interface, how can I determine which player is doing that from the CanCraft hook?  I'd like to block crafting a specific item this way, and send an explanatory message to the player who tried to craft.

https://umod.org/documentation/games/rust#cancraft

Generally you'd get the BasePlayer component from the first argument provided by the hook. IntelliSense may be able to help you with this, otherwise try GetComponent from Unity if a field or method isn't available under those.