First of all, how lovely that your little one loves the dog so much. My dog tripped me over recently and badly broke my leg so I’m less enamoured with the dog than your 13 month old! It seems your son just wants to play with the dog and doesn’t understand the limits of that play or the limits of the dog’s patience. It’s impressive the dog hasn’t expressed his displeasure so far. It’s a good opportunity for you to teach your son about appropriate behaviour around the dog and maybe it’s time to set a limit.
I think the limits are not pulling Cooper’s fur, grabbing Cooper’s face, or poking Cooper in the eye. But, obviously if he does other things to Cooper, they’ll need to be included in your list.
Perhaps, when he is rough with Cooper, you can say, “pulling Cooper's fur hurts him, I’m not going to let you pull his fur” and then, if he does it again, it might be a good idea to remove him from the situation. If the child does go to pull the fur or poke his eyes or even, as I once did, to try to put a full face of make-up on the dog, it’s best that you remove your son and take him to another room and explain again, in the same gentle and calm, but no-nonsense, voice that you will not let him hurt Cooper.
If he rages and cries or is angry, that is okay. I imagine he will lash out because (1) he really does love the dog, (2) he doesn’t want to leave Cooper and (3) he feels embarrassed because he did not understand the limits of his own strength.
It would be good if you could sit with him and listen to his feelings. We can say something along the lines of “I can see you’re disappointed that you may have hurt Cooper, but pulling his fur/poking him/grabbing him could hurt him”.
Research shows that dogs might be calm on the outside but can be experiencing extreme stress, as you seem to be aware from your response, and it’s great that you want to protect Cooper from your son’s overtly too-strong displays of affection. However, you’re right to be cautious, as the majority of dog related injuries occur in children between the ages of 0-4, with wrists and hands the most common injury.