ios-concurrencylisted

# iOS Concurrency Skill ## Core Rules 1. **Use async/await for ALL new asynchronous code.** Do not use completion handlers or Combine for async operations in new code. 2. **Use structured concurrency (Task, TaskGroup).** Avoid unstructured task leaks. Prefer `async let` or `TaskGroup` over spawning loose `Task {}` blocks. 3. **Mark UI-updating code with @MainActor.** SwiftUI views are already `@MainActor`-isolated. UIKit code that touches UI must run on `@MainActor`. 4. **Use actors for shared mutable state** instead of locks, semaphores, or serial dispatch queues. 5. **All types crossing actor boundaries must be Sendable.** The compiler enforces this in strict concurrency mode. 6. **Prefer value types (struct, enum) for Sendable.** They are implicitly Sendable when all stored properties are Sendable. 7. **Use `withCheckedContinuation` to bridge callback-based APIs** to async/await. Never resume a continuation more than once. 8. **Use `AsyncStream` for bridging delegate/callback patterns** to `AsyncSequence`. 9. **`Task.detached` is rarely needed.** Use `Task {}` with explicit actor isolation instead. Detached tasks lose actor context and priority inheritance. 10. **Always handle Task cancellation cooperatively.** Check `Task.isCancelled` or call `try Task.checkCancellation()` at appropriate points. ## Decision Guide | Scenario | Solution | |----------|----------| | Single async operation | `async func` / `Task {}` | | Multiple independent operations | `TaskGroup` / `asyn