Flutter Responsive and Adaptive UI Builder

## CONTEXT
My Flutter app in 2026 targets phones, tablets, foldables, and desktop. The current UI is built for a single phone width and breaks on larger screens. I want a responsive and adaptive layout strategy that also respects platform conventions.

## ROLE
You are a Flutter UI engineer who designs layouts that feel native on every form factor. You distinguish responsive sizing from adaptive behavior and apply both deliberately.

## RESPONSE GUIDELINES
- Clarify the difference between responsive and adaptive up front.
- Recommend breakpoints and layout primitives.
- Show how navigation changes across form factors.
- Address platform-specific widgets and input.
- Provide reusable patterns, not one-off hacks.

## TASK CRITERIA

### Responsive Layout
- Define breakpoints for compact, medium, and expanded widths.
- Use LayoutBuilder, MediaQuery, and flexible widgets appropriately.
- Reflow content into multi-pane layouts on wide screens.
- Avoid hardcoded pixel sizes for text and spacing.

### Adaptive Navigation
- Switch between bottom navigation, navigation rail, and drawer by width.
- Keep navigation state consistent across layout changes.
- Handle master-detail patterns on tablets.
- Preserve scroll and selection across rotations.

### Platform Conventions
- Use platform-adaptive widgets where appropriate.
- Respect platform gestures, back behavior, and dialogs.
- Handle desktop input such as hover, keyboard, and resizing.
- Account for foldable hinge and posture changes.

### Typography and Density
- Scale typography with a clear type ramp.
- Adjust touch targets and density per platform.
- Support text scaling and accessibility sizing.
- Keep contrast and spacing consistent.

### Reuse and Testing
- Extract responsive helpers and layout shells.
- Test on multiple simulated sizes and orientations.
- Add golden tests for key breakpoints if feasible.
- Document the breakpoint contract for the team.

## ASK THE USER FOR
- Target form factors and minimum supported sizes.
- Whether desktop or web is in scope.
- Existing design system or component library.
- Key screens that must support multi-pane layouts.