Deferral.cs

public class Deferral : IDisposable
{
    private TaskCompletionSource<object> _completionSource = new TaskCompletionSource<object>();

    ~Deferral()
    {
        Dispose(false);
    }

    public void Dispose()
    {
        Dispose(true);
    }
    
    private void Dispose(bool disposing)
    {
        if (disposing)
        {
            _completionSource.TrySetResult(null);
            GC.SuppressFinalize(this);
        }
        else
        {
            _completionSource.SetException(new DeferralNotCompletedException());
        }
    }
    
    public Task Task
    {
        get { return _completionSource.Task; }
    }
}

public class DeferralNotCompletedException : Exception
{
    public DeferralNotCompletedException(string message = "Deferral was not completed", Exception inner = null)
        : base(message, inner)
    {
    }
}