Adaptive Layout — iPhone & iPad Core Principle Let SwiftUI adapt automatically. Never check or for layout decisions. Use size classes and adaptive containers instead. Navigation NavigationSplitView (primary pattern for list-detail) Use for ANY list-detail flow. It collapses to on iPhone and shows sidebar+detail on iPad — zero conditional code. Three-column pattern (sidebar categories → list → detail): Use ONLY for purely linear flows (onboarding, checkout). Size Classes | Context | horizontalSizeClass | |---|---| | iPhone portrait | | | iPhone landscape | | | iPad full-screen | | | iPad Split…