In a small bowl, combine the chicken stock with the miso, wine, sugar and cornstarch. Heat a large wok or skillet until very hot, about 3 minutes. Add the oil and chiles and cook over high heat until the chiles darken, 1 to 2 minutes. Add the garlic and cook for 10 seconds, stirring constantly. Add the bok choy, season with salt and stir-fry until the leaves are wilted and the stalks are crisp-tender, about 5 minutes. Stir the miso sauce, add it to the wok and stir-fry, until thickened slightly, about 2 minutes longer.