1. 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.
2. 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).
3. 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.
4. 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).
5. 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.
Cutting the cranberries in half (step 2) is time-consuming, but it makes a big difference in the texture of the finished salad. The cranberries may be steeped in sugar syrup (step 3) up to 1 day ahead; cover and chill in syrup (cranberries' color will deepen).