swift-concurrency

First confirm the code is truly UI-bound. If so, isolate the caller with @MainActor or wrap the call in await MainActor.run. If the work is not UI-related, move it off the main actor instead of adding isolation as a blanket fix.

Add a new async method alongside the old one, replace completion handlers with return values or throws, and bridge with withCheckedThrowingContinuation when the underlying API is still closure-based. Remove optional unwrapping since async APIs return non-optional values.

Use an actor in async contexts when you need logical isolation of mutable state. Use Mutex (iOS 18+, macOS 15+) for synchronous access, legacy non-async code, or fine-grained locking where async overhead is unnecessary.

NSManagedObject is not Sendable and must not cross context or actor boundaries. Pass NSManagedObjectID instead, access contexts through perform, and mark manually generated subclasses as nonisolated when default MainActor isolation is enabled.

Sendable warnings appear when values cross isolation boundaries without safe transfer semantics. Prefer immutable value types, keep access inside one actor, and reserve @unchecked Sendable for cases with a documented safety invariant and removal plan.

AsyncStream bridges callbacks and delegates to async iteration but supports only a single consumer. AsyncChannel from the AsyncAlgorithms package provides backpressure and point-to-point delivery for producer-consumer scenarios with multiple senders.