Preheat the oven to 350°. Season the chicken with salt and pepper. In a large enameled cast-iron casserole, heat the olive oil. Add half of the chicken along with the backbone and neck and cook over moderately high heat until browned, about 4 minutes per side. Transfer the chicken to a plate and repeat with the remaining pieces.
Pour off all but 2 tablespoons of the fat in the casserole. Add the onion, smashed garlic cloves, raisins and chopped walnuts to the casserole and cook over moderate heat, stirring occasionally, until the onion is softened and golden brown, about 7 minutes. Add the saffron water, chicken broth, pomegranate juice, cardamom, allspice, dried lime and cinnamon stick and bring to a boil over moderately high heat. Return the chicken pieces to the casserole, skin side up, along with any accumulated juices. Cover and braise the chicken in the oven for about 35 minutes, until the breasts are cooked through.
Transfer the chicken breasts to a medium bowl and keep them warm. Continue braising the dark meat pieces for about 15 minutes, until the legs are cooked through. Transfer the legs to the bowl. Discard the chicken back and neck.
Boil the braising liquid over high heat until it is reduced to 3/4 cup, about 15 minutes. Discard the dried lime, cardamom, allspice and cinnamon stick. Add the red wine vinegar and season the sauce with salt and pepper. Return the chicken pieces to the sauce and simmer them gently until they are heated through, about 3 minutes. Transfer the chicken stew to shallow bowls and serve with couscous.