flutter-performancelisted

Resolve `UFIL_ROOT` to the plugin root containing this skill. Claude Code may provide `CLAUDE_PLUGIN_ROOT`; Codex can resolve it from the installed skill path. ## Flutter Performance Patterns (GM Standard) Rules + decision matrices for performance-critical Flutter UI choices. For full rationale, profiling workflow, and extended examples, read `${CLAUDE_PLUGIN_ROOT}/docs/PERFORMANCE.md`. > **Note on colors in examples**: GM standard requires every color to come from generated `AppColors` (flutter_gen → `colors.gen.dart`). The snippets below use raw `Color(0x..)` / `Colors.xxx` only to keep the performance contrast self-contained — production code MUST use `AppColors.<name>`. See the Color rule in `${CLAUDE_PLUGIN_ROOT}/CLAUDE.md` and the implementer agent. --- ## 1. Const Class vs Helper Method (CRITICAL) **Rule:** Prefer `const` widget class over helper method when the widget is reused or rebuilt frequently. Helper methods are called every rebuild and cannot be cached by Flutter; `const` widgets are instantiated once and reused. ### ❌ Helper method (cannot be cached) ```dart Widget _buildPixelContainer() { return Container( width: 6, height: 6, decoration: BoxDecoration(color: Colors.red.shade400, borderRadius: BorderRadius.circular(1)), ); } ``` ### ✅ Const widget class (cached by Flutter) ```dart class PixelBox extends StatelessWidget { const PixelBox({super.key}); @override Widget build(BuildContext context) { return Container( width: