Wee Fong Ehlers calmly plops a preportioned container of mushrooms, chopped carrots, and cabbage into her sizzling wok, unaware of the iPad screen glowing red behind her or the customer waiting at the register outside. “Mama!” exclaims Alex Ehlers from his post as cashier, skidding past a table stocked with Justin’s peanut butter cups, roast beef sandwiches, and $12 fruit juices to enter Ehlers’s universe: the kitchen at Royal Blue Grocery, an upscale corner store, on Congress Avenue in downtown Austin. “There’s an order from yesterday morning. Are you gonna talk to him?” It’s the mid-lunch rush. Ehlers nods to her 21-year-old son and quickly prepares a to-go container with stewed beef, coconut rice, and cucumbers, adding a complimentary Thai green tea to the order as a…