Instagram Wipes localStorage on Navigation. Here's How We Keep Multiplayer Sessions Alive. A teacher shares a bingo game link to her class group chat. Half the students open it in Instagram's in-app browser. They tap a cell, switch to check a notification, come back. Their game session is gone. They're staring at a fresh board with none of their claims. This happened in production on BingWow within the first week of launch. The root cause Instagram, TikTok, Snapchat, and Facebook Messenger all use in-app WebView browsers. These are not Safari or Chrome. They're stripped-down renderers with restrictions that vary by platform and OS version. The critical one: some WebViews clear localStorage on navigation events. Not every time. Not on every device. But often enough that "store session in localStorage" is a broken architecture for any app where users arrive via social media links. Our game sessions stored the player ID, room code, and display name in localStorage.…