TaskMaster Pro

Two people drag the same card at the same time. That is the whole problem, and every task app has to answer it. The naive version broadcasts each change and lets the last write win, which looks fine with one browser open and produces cards that jump under people's hands the moment there are two. Drag and drop made it worse, because a drag is not one event, it is a long gesture where the local view has already moved and the server has not agreed yet. Getting optimistic and confirmed state to converge without the card visibly snapping back is most of the real work here, and none of it shows in a screenshot.