Preheat the oven to 300°. Cook the asparagus in a large saucepan of boiling salted water until tender, about 8 minutes, then drain thoroughly.
In a large skillet, heat 1/2 inch of oil until shimmering. Season the crabs with salt and pepper and dredge in the cornstarch. Add 4 of the crabs to the skillet and fry over moderately high heat until very crunchy, about 4 minutes for the first side and 3 minutes for the second. Transfer to a heatproof plate and keep warm in the oven. Fry the remaining crabs, then keep them warm in the oven while making the sauce.
In a large skillet, heat the 2 tablespoons of oil. Add the shallots and cook over moderately high heat until lightly browned, about 2 minutes. Add the wine and cook until reduced by about half, 2 to 3 minutes. Add the oyster sauce and simmer until slightly thickened, about 2 minutes. Add the asparagus and lime juice; toss to coat. Transfer the asparagus and sauce to 4 dinner plates. Top with the crabs and cilantro and serve at once.