In a 4- to 6-quart pan, combine wild rice, salt, and 1 quart water. Bring to a boil over high heat; cover, reduce heat, and simmer until rice is tender to bite and most grains have just split open, 45 to 60 minutes. Drain in a colander and let cool.
Meanwhile, spread walnuts in a baking pan and toast in a 325° regular or convection oven until lightly golden under skins, about 10 minutes. Coarsely chop. Sort cranberries, discarding any stems and bruised or decayed fruit; cut each cranberry in half (see notes).
In a 2- to 3-quart pan over medium-high heat, stir the sugar and 1/2 cup water until the sugar is dissolved and mixture boils. Remove from heat; stir in the halved cranberries. Gently stir occasionally until insides of cranberries have turned red but are still firm, 8 to 12 minutes (see notes). Pour through a fine strainer into a bowl, reserving the cranberry-sugar syrup.
In a large bowl, gently mix wild rice, cranberry halves, oil, and vinegar. Stir in 2 tablespoons cranberry syrup; taste and add up to 1/4 cup more syrup to sweeten and moisten salad as desired (reserve remaining syrup for other uses). Cover and chill for at least 4 hours or up to 1 day (see notes).
Stir in all but 2 tablespoons of the green onions, along with the walnuts and dried cranberries (if using). Sprinkle with remaining green onions just before serving.