Place stock, clam juice, and saffron in a medium saucepan over medium-high heat. Bring to a boil, cover, and reduce heat; simmer 15 minutes. Remove from heat; set aside.
Prepare an ice bath. Bring a medium saucepan of water to a boil, and blanch sugar snap peas until bright green and just tender, about 1 minute. Using a slotted spoon, transfer peas to ice bath; let cool. Drain, and set aside.
Coat a paella pan (or a 6-quart Dutch oven that measures 11 inches in diameter and 5 inches in height) with cooking spray; set over medium-high heat. Add sausage, and cook until well browned, turning, about 5 minutes.
Add shrimp, and cook 1 1/2 minutes. Add squid, and cook until opaque, about 1 1/2 minutes more. Transfer seafood and sausage to a plate, and set aside.
Add onion, garlic, and bell peppers to paella pan; saute until onions are translucent, about 3 minutes. Add uncooked rice; saute until translucent, 1 to 2 minutes more. Add 4 cups reserved stock mixture; bring to a boil. Reduce heat to medium low, and cover. Cook until most liquid has been absorbed and the rice is just tender, about 10 minutes.
Meanwhile, place remaining cup of stock mixture, cockles, and mussels in a saute pan over medium-high heat. Cover, and bring to boil. Cook until all shells have opened, 2 to 3 minutes; discard any that remain closed.
Add paprika, black pepper, tomatoes, shrimp, squid, and sausage to rice mixture; combine. Add cockles, mussels, and cooking liquid to mixture, being careful to leave behind any residue in saute pan. Stir in parsley; garnish with peas. Serve immediately.