Crash in Combine Related to Swift 6 Concurrency

Using Swift
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2

I've run into the same problem, and you don't really need @unchecked Sendable to trigger it either, you just need old-fashioned APIs that don't understand Swift concurrency. For instance, I managed to make this minimal test case:

final class TestCrash: XCTestCase {
    let subject = CurrentValueSubject<Int, Never>(1)

    @MainActor
    func testCrash() async throws {
        let cancellable = subject.sink { value in
            print("\(value)")
        }

        performSelector(inBackground: #selector(triggerSubject), with: nil) // Crashes
        //perform(#selector(triggerSubject), with: nil) // Does not crash

        try await Task.sleep(nanoseconds: 1000000000)

        _ = cancellable
    }

    @objc func triggerSubject() {
        subject.send(2)
    }
}

I feel Swift is being a bit too over-eager to first apply @MainActor and then defend it here.