Advanced Compose Multiplatform UI patterns for shared composables. Use when working with visual UI components, state management patterns (remember, derivedStateOf, produceState), recomposition optimization (@Stable/@Immutable visual usage), Material3 theming, custom ImageVector icons, or determining whether to share UI in commonMain vs keep platform-specific. Delegates navigation to android-expert/desktop-expert. Complements kotlin-expert (handles Kotlin language aspects of state/annotations).