Use Apple's Combine framework for reactive streams — Publishers and Subscribers, common operators (map/filter/debounce/removeDuplicates/combineLatest), @Published, sink and assign, AnyCancellable lifetime management, and bridging Combine with async/await. Also explains when NOT to use Combine and to prefer async/await + Observation instead. Use when working with existing Combine code, debouncing/throttling inputs, observing NotificationCenter/Timer publishers, or reactive pipelines on iOS 26+.
