Set a colander over a bowl. Add the zucchini to the colander and toss with 1 teaspoon of salt. Let stand for 20 minutes. Squeeze the zucchini dry.

In a large, nonreactive skillet, heat the olive oil. Add the chopped shallots and season with salt and pepper. Cook over moderate heat until softened, about 3 minutes. Add 1/4 cup of the wine and cook until evaporated, about 2 minutes. Stir in the corn and 1/2 cup of water. Cover and cook until the corn is tender, about 4 minutes. Stir in the zucchini and cook until heated through, about 2 minutes. Season with salt and pepper, cover, and keep warm.

In a large, nonreactive saucepan, combine 2 cups of the wine with the thyme, bay leaf, the halved shallot, and 2 cups of water and bring to a simmer. Season the salmon with salt, add the fillets to the saucepan and cook at a bare simmer over low heat, turning once, about 6 minutes. Transfer the salmon to a plate and pat dry with paper towels. Discard the poaching liquid.

Add the remaining 1/2 cup of wine to the saucepan and bring to a simmer. Whisk in the butter, 1 tablespoon at a time, until thoroughly incorporated. Season with salt. Stir the basil into the vegetables and transfer to plates. Nestle the salmon into the vegetables, top with the butter sauce, and serve.