1. Performance & Rendering

Const-First: Every widget that can be const MUST be const.
Lazy Rendering: Use SliverList.builder or SliverGrid.builder for lists > 10 items.
Repaint Boundaries: Wrap complex animations in RepaintBoundary.
Isolate Parsing: Use compute() or Isolate for JSON > 1MB.
BuildContext Safety: Check mounted before using context across async gaps.

2. Design Tokens (Theming)

Use AppColors, AppSpacing, AppRadius, and AppTypography. NEVER hardcode raw values.

Colors: Use context.colorScheme.primary or AppColors. Support light/dark modes.
Spacing: Use AppSpacing.sm (8), AppSpacing.md (16), etc. Use SizedBox for gaps.
Radius: Use AppRadius.md (12) for consistent rounding.
Typography: Use context.textTheme.bodyMedium. Support text scaling.

Single Responsibility: Each component has one clear purpose.
Parameterization: Expose parameters for customization.
Complexity: Extract widgets or code blocks used multiple times into core/views/widgets.
Keys: Assign Key('feature_action_id') to interactive widgets for test access.

Extraction: STRICTLY prohibit private _build*() methods. Extract into separate widget classes.
Slivers: Prefer CustomScrollView with Slivers for non-trivial scrollable layouts.
FAB: Use Floating Action Buttons for primary positive actions (Add, Create).
Scroll Padding: Add dynamic bottom padding when a FAB or BottomBar is present to prevent overlap.
Sheets vs Screens: Prefer full Scaffold screens over ModalBottomSheet for complex forms.

Mobile First: Design for mobile, then adapt for tablet (600-840) and desktop (>840).
Measure & Branch: Use MediaQuery.sizeOf(context) for layout decisions; LayoutBuilder for widget constraints.
Rules: Never lock orientation. Support keyboard navigation and hover effects.

States: Always handle Loading, Error, and Empty states with clear messaging.
Accessibility: Include Semantics labels. Ensure 48x48 dp touch targets. WCAG AA contrast.