Your app works. Then a user opens it in a second tab, and things start going wrong in ways that never show up in testing. Both tabs poll the server, so your request volume doubles for one user. Both hold a WebSocket, so your connection count is wrong and your server thinks you have twice the traffic you do. Both raise the same desktop notification, so it appears twice. The user signs out in one tab and the other carries on as though nothing happened, still showing their data, still refre...