How do you bridge repeated events, GCD and Combine into async code with AsyncStream?

When an API delivers many values over time (delegate callbacks, notifications, location updates, a Combine publisher) wrap it in an AsyncStream (non-throwing) or AsyncThrowingStream. You build it with a closure that receives a continuation: call continuation.yield(value) for each event, finish() (or finish(throwing:)) when done, and set continuation.onTermination to clean up (remove the observer, stop the location manager) when the consumer stops or the task is cancelled. The consumer then writes for await value in stream { … }, which is cancellable and ends when the task is cancelled. A stream has a buffering policy: the default .unbounded keeps every value until consumed, .bufferingNewest(n) keeps only the latest n (right for state such as the current location: with newest-1, five rapid yields leave only the last), and .bufferingOldest(n) drops later ones. A stream is single-consumer by default; iterating it from two tasks splits the values.

Other bridges. A Combine publisher has a .values property that returns an async sequence (handle that it is not backpressure-aware in the same way); the other direction is a Future wrapping a Task. A GCD API with a completion handler becomes async through a continuation; moving from async to a GCD API means calling it inside a task, and a DispatchQueue can be turned into a custom actor executor if you must keep ordering with legacy code. Use AsyncStream.makeStream() to get the stream and continuation separately, which is convenient when the producer lives elsewhere. Test bridges for cancellation (the underlying resource is released) and for the exactly-once or ends-once contract.