From OP: "We took him to a local university vet medical school. He only weighs 6 lbs so we were concerned about how much he had, plus there was some chocolate in the cookie so just wanted to be safe. What was funny is they weren't phased at all - clearly not the first time they had seen a stoned animal. He's generally a very happy dog but this was definitely a dose of paranoid pot. In addition to not being able to stand, he was very jittery and afraid. Poor guy :( They kept him about 10 hours, induced vomiting and gave him some kind of charcoal activated something to help soak up the rest. He was pretty normal by the time we got him home."
Accidents happen. Luckily these pet owners were smart enough to take their little friend to the vet. Peanut is feeling much better now!