Went to a revolving sushi bar tonight. Everything was automated. They even had a touchpad where you can put in orders (like miso ramen soup), which get delivered by a belt. The only thing the servers did was sit us and bring us water. We asked them to replace a leaking soy sauce container and they never did. We tipped 0$ -- there was essentially no service. I kinda felt bad, but talking it over with my wife, I couldn…
I also don't understand tipping at food carts. Customers stand in a line to pay and get their food, and are also expected to tip (either via Square or through tip jars). Edit: the expectation is generally implicit, and while standing in line, I can't help but notice that most customers hit the minimum tip percentage on Square, which is usually 15%
Ultimately, I think right now the social expectation of tipping in this situation is in limbo- whether you do or don't, it's ok.