Cancellation is a request; stale results still need a guard

First, build a mental model

A CancellationToken communicates that work is no longer wanted. Cooperating operations decide how to observe it. A result-order guard separately decides whether a completed result still belongs to the current request.

1. Pass the token through methods into cancelable I/O and waits instead of accepting it and ignoring it.
2. Canceled task-based operations commonly surface OperationCanceledException when awaited; handle expected cancellation separately from a genuine failure.
3. Cancellation does not undo a committed database write or guarantee that a remote server never received a request.
4. A monotonically increasing request identity can reject stale results even when a dependency ignores or races with cancellation.

static async Task<int> LoadAsync(CancellationToken token)
{
    await Task.Delay(1000, token);
    return 42;
}

using var source = new CancellationTokenSource();
source.Cancel();
try
{
    int value = await LoadAsync(source.Token);
    Console.WriteLine(value);
}
catch (OperationCanceledException) when (source.IsCancellationRequested)
{
    Console.WriteLine("cancelled");
}

1. Request cancellation

   The token is already canceled before LoadAsync is called.

2. Observe

   Task.Delay observes that token; await propagates cancellation.

3. Handle

   The filtered cancellation handler runs instead of printing a fabricated result.