Flutter Guideline: Navigation — Handle back button (PopScope). Description: Android back behavior and predictive back (Android 14+). Do: Use PopScope widget (WillPopScope is deprecated). Don't: Use WillPopScope. Good Example: PopScope(canPop: false, onPopInvoked: (didPop) => ...). Bad Example: WillPopScope(onWillPop: ...). Severity: High. Docs: https://api.flutter.dev/flutter/widgets/PopScope-class.html.