Shareplay Activities

This covers building real-time shared experiences on Apple platforms using GroupActivities and SharePlay. You'll use it when you want to sync media playback across FaceTime calls, build collaborative features like shared drawing canvases, or keep game state synchronized between participants. The skill walks through the full setup: defining activities with proper metadata, managing session lifecycle and participant changes, sending reliable or unreliable messages for state sync, and wiring up AVPlayer's built-in playback coordinator. It targets Swift 6.3 and iOS 26+, includes entitlement configuration, and covers both in-call activation and starting SharePlay from your app when no conversation is active. The reliable versus unreliable messenger distinction is especially useful for balancing responsiveness with consistency.