#isolation, @isolated(any), Sendable: what effect do they have on where an async function is executed?

main.swift

import Foundation

func inheritCallerIsolation(
    isolation: isolated (any Actor)? = #isolation,
    // Closure executes on different threads, depending on attributes
    operation: () async -> Void
//    operation: @Sendable () async -> Void
//    operation: @isolated(any) () async -> Void
//    operation: @isolated(any) @Sendable () async -> Void
) async {
    print("inheritCallerIsolation thread=\(currentThread())   isolation=\(isolation)")
    await operation()
}

func nonIsolatedFunc() async {
    print("nonIsolatedFunc        thread=\(currentThread())")
}

Task.detached {
    print("Task started           thread=\(currentThread())")
    await withTaskGroup(of: Void.self) { group in
        print("Task group started     thread=\(currentThread())")
        group.addTask { @Sendable @MainActor in
            print("Child task started     thread=\(currentThread())")
            await inheritCallerIsolation {
                print("Closure started        thread=\(currentThread())")
                await nonIsolatedFunc()
                print("Closure ending         thread=\(currentThread())")
            }
            print("Child task ending      thread=\(currentThread())")
        }
    }
    print("Task group ended       thread=\(currentThread())")
    print("Task ending            thread=\(currentThread())")
}

func currentThread() -> String {
    let thread = Thread.current
    if thread.isMainThread {
        return "main"
    } else if let name = thread.name, !name.isEmpty {
        return name
    } else if let numberMatch = String(describing: thread).firstMatch(of: /{number = (\d+),/) {
        let number = numberMatch.output.1
        return String(number)
    } else {
        return String(describing: thread)
    }
}