Building tractor (升级) as an online card game

Introduction This COVID-19 pandemic has left me with lots of free time spent in front of a computer at home. I’d been spending time with my friends playing various videogames online (the Jackbox Party Pack games work reasonably well over Discord or Zoom), and my fiancée suggested that we try to play tractor online… but I couldn’t find one that was easily available over the internet! What’s tractor, anyways? Tractor is a trick-taking card game popular in China, played with four or more players and with multiple decks.