I made this shit up

ExchangeTypes.cs

// Anything that can fire a one shot callback
interface IEventable
{
   bool IsTriggered { get; set; }
   void Register(Action<object> callback, object state);
}

class Task : IEventable { }
class ManualResetEvent : IEventable { }
class CancellationToken : IEventable { } 

public class Sample
{
    ManualResetEvent e = new ManualResetEvent();
    
    async Task Main()
    {
        // Cancel DoSometingFancy when DoSomethingBoring completes
        await DoSometingFancy(DoSomethingBoring());
        
        // Cancel DoSometingFancy when the ManualResetEvent event is triggered
        await DoSometingFancy(e);
    }
    
    async Task DoSomethingBoring()
    {
       // I can await the ManualResetEvent because it implements IEventable
       await e;
    }
    
    async Task DoSometingFancy(IEventable cancellationToken)
    {
         await Task.Delay(1000);
         // Pretend like we're doing something long running and waiting for cancellation
         await cancellationToken;
    }
}