ui-package

# UI Package Best practices for creating a Flutter UI package — a reusable widget library that builds on top of `package:flutter/material.dart`, extending it with app-specific components, custom design tokens via `ThemeExtension`, and a consistent API surface. > **Theming foundation:** This skill focuses on UI package structure, widget APIs, and testing. For foundational Material 3 theming (`ColorScheme`, `TextTheme`, component themes, spacing constants, light/dark mode), see the **Material Theming** skill (`/material-theming`). The two skills are complementary — Material Theming covers how to set up and use `ThemeData`; this skill covers how to extend it with `ThemeExtension` tokens and package reusable widgets around it. ## Core Standards Apply these standards to ALL UI package work: - **Scaffold from the `app_ui_package` template** — create the package with the Very Good CLI MCP tool, `subcommand: 'app_ui_package'`. Never `flutter_package`, never `dart_package`, never `flutter create --template=package`; those produce a bare package with none of the theme, barrel, test-helper, or Widgetbook scaffolding below - **Build on Material** — depend on `flutter/material.dart` and compose Material widgets; do not rebuild primitives that Material already provides - **One widget per file** — each public widget lives in its own file named after the widget in snake_case (e.g., `app_button.dart`) - **Barrel file for public API** — expose all public widgets and theme classes through ...