cancel_03.cs

class Client
{
    public TimeSpan Timeout { get; }

    public Client(TimeSpan timeout)
    {
        this.Timeout = timeout;
    }

    public async Task SendAsync(CancellationToken cancellationToken = default)
    {
        // Create concatenated new CancellationTokenSource
        using var cts = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
        cts.CancelAfter(Timeout);

        await SendCoreAsync(cts.Token);
    }

    // snip...
}