Debugging Android Backdrop Persistence: A Capacitor Story

Porting a complex React app like Scratch-GUI to mobile using Capacitor can surface bugs that don't appear on desktop. Recently, we fixed a frustrating issue: backdrop edits (drawings and erasures) weren't saving in .sb3 files on Android. Here's what went wrong and how we fixed it. 1. The Main Problem: Edits Weren't Saving Two issues caused backdrop changes to disappear when saving. A. Storage Configuration Typo In storage.js , we had a typo in the asset storage config. It was trying to use invalid "create" and "update" helpers, triggering failed network requests in the Capacitor environment. Fix: Corrected the typo and simplified addWebStore to only use the GET helper for local assets. B. Save Button Didn't Commit Pending Edits The Paint Editor (from scratch-paint) normally saves changes when you click away from the canvas. On Android, clicking the "Save" button didn't trigger that "focus lost" event, so the latest drawing wasn't being saved. Fix: Added a manual sync step before saving