Hook for “Add to Cart” action?

I want to do something just before or just after a product is added to the cart, but I can’t find the action hook for it. I’ve checked the docs, but don’t see anything. Am I missing it?

If it helps, here’s what I’m trying to do: when a customer clicks the Add To Cart button, I want to check if that product already exists in the cart. If it does, I want to delete the other versions of the product from the cart, so only the most recent one is added. I have the code to do that, but can’t find the action/hook I need.

Thanks!