Unsure why warnings show in the second example unless the method is marked @mainactor

MainActorIsolationSample.swift

import AVFoundation

class Foo {
    var x: AVAudioFile?

    func someOtherMethod() async throws {
        x = try AVAudioFile(forReading: URL(fileURLWithPath: "/path/to/file.m4a"))
    }
    
    //@MainActor annotation is not needed here and there are no warnings, why is it needed below?
    func bar(completionHandler: @escaping (Error?)->Void) {
        Task {
            do {
                try await self.someOtherMethod()
                completionHandler(nil)
            } catch {
                completionHandler(error)
            }
        }
    }
}

extension AVAssetExportSession {
    //@MainActor //uncomment this to silence warnings
    func export(to url: URL, as fileType: AVFileType, completionHandler: @escaping (Error?)->Void) {
        if #available(iOS 18, macOS 15, tvOS 15, visionOS 2, *) {
            Task {
                do {
                    try await export(to: url, as: fileType, isolation: #isolation)
                    completionHandler(nil)
                } catch {
                    completionHandler(error)
                }
            }
        } else {
            outputURL = url
            outputFileType = fileType
            
            Task {
                await withCheckedContinuation { continuation in
                    exportAsynchronously {
                        continuation.resume()
                    }
                }
                
                completionHandler(error)
            }
        }
    }
}

Right away, I am definitely seeing warnings here. And that makes sense, the stuff going in to Task has to be Sendable. Making this MainActor prevents the isolation domains from needing to be crossed.

        // @MainActor annotation is not needed here and there are no warnings, why is it needed below?
	func bar(completionHandler: @escaping (Error?) -> Void) {
		Task {
			do {
// WARNING: Capture of 'self' with non-sendable type 'Foo' in a `@Sendable` closure; this is an error in the Swift 6 language mode
				try await self.someOtherMethod()
// WANRING: Capture of 'completionHandler' with non-sendable type '((any Error)?) -> Void' in a `@Sendable` closure; this is an error in the Swift 6 language mode
				completionHandler(nil)
			} catch {
				completionHandler(error)
			}
		}
	}

That is odd @mattmassicotte — I don't get those warning in Xcode 16 Beta

This had made me assume the Task inherits the isolation domain from the caller of the function it is defined in (not sure if that even makes sense?)