Apply Reactive / Observer Patterns

Background: Native [platform] app. iOS uses Combine; Android uses Kotlin
Flow. Here's the reactive scenario I'm modeling:
[describe—e.g., search-as-you-type, combining auth state with profile
data, a stream that several screens observe]

Use case: Implement this with idiomatic reactive operators instead of
manual callbacks and mutable shared state.

Implementation details:
- iOS (Combine): pick the right operators (map, flatMap, combineLatest,
  debounce, removeDuplicates, switchToLatest) and handle cancellation
  with the SwiftUI lifecycle
- Android (Flow): pick the right operators (map, flatMapLatest, combine,
  debounce, distinctUntilChanged, stateIn) and the right collection scope
- Handle errors within the stream (don't let one failure kill it)
- Avoid retain cycles (iOS) / leaked collectors (Android)

Layer & dependencies: The stream is owned by the view model / state
holder and exposed as read-only state to the view.

Deliverable: The reactive pipeline for both platforms (or just mine),
with operator choices explained, error handling, and the common pitfall
to watch for in this specific scenario.