Cut the chicken into 1/8th inch strips, in a large stockpot, boil them in 4 cups of water for 3 minutes until cooked, drain, rinse, and set aside.
Rinse the pot out, place it over medium heat and add the chicken stock, reserving ¾ cup. Add the soy sauce, dark soy, white vinegar, white pepper, tofu, bamboo shoots, mushrooms, sesame oil, and the cooked chicken.
Stir to combine, bring to a simmer, stirring occasionally.
While you are waiting for the soup to come to a simmer, stir the cornstarch with the reserved ¾ cup of chicken stock in a small bowl until fully combined with no lumps.
When the soup comes to a simmer, slowly stream in the cornstarch mixture while stirring the pot. Make sure no cornstarch gets stuck on the bottom of the pot. Continue to cook until the soup has thickened, about 3 minutes.
Use a ladle to add the eggs. We are going to stir the soup, then toss some of the beaten egg into the soup with the ladle, then again stir the egg in through the soup. Do this in about 6 batches. This will make the egg ribbon effect. Taste, adjust seasoning if needed, and serve with a garnish of scallions.