How is baby bok choy cooked in Shanghai?
I've never cooked or eaten in Shanghai, however, based on a rudimentary knowledge of Chinese cooking, cooking it at home, and with the support of Google, I would guess the following:

Bok choy is blanched for a short time in boiling water, and then refreshed in an ice bath.

It is stir fried in a very hot wok, probably with some garlic.

A slurry of cornstarch is added. It is made with water, soy, perhaps some sesame oil. This produces the light sauce.

I suspect that sometimes, fermented black bean might be added.