macOS application architecture patterns covering App protocol (@main), Scene types (WindowGroup, Window, Settings, MenuBarExtra), multi-window management, NSApplicationDelegateAdaptor for AppKit lifecycle hooks, Info.plist configuration (LSUIElement for menu bar apps, NSAccessibilityUsageDescription), entitlements for sandbox/hardened runtime, and project structure conventions. Use when scaffolding a new macOS app, configuring scenes and windows, setting up menu bar apps, or resolving macOS-specific lifecycle issues. Corrects the common LLM mistake of generating iOS-only app structures.