Action throwing OperationCanceledException/TaskCanceledException silently stops the polling loop; RethrowExceptions() reports nothing #66

What's wrong

If the user's Action throws, the next tick's TryRun() rethrows that exception inside the polling loop's async lambda (IntervalAction/IntervalAction.cs, ~lines 221–240). When an async method ends with an OperationCanceledException, its task becomes Canceled, not Faulted. TaskCanceledException derives from OperationCanceledException, and HttpClient throws it on a timeout, so this is not a rare case.

Once that happens, PollingTask.Status == Canceled and PollingTask.Exception == null. RethrowExceptions() (line ~299) only looks at PollingTask.Exception, so it returns normally. The loop has stopped for good, but ShouldPoll still reads true and nothing reports the failure.

Repro

PollingInterval = 20ms, ActionInterval = 0, Action = () => throw new TaskCanceledException("http timeout"). After 500 ms:

• the action has run once
• the polling task is Canceled
• RethrowExceptions() throws nothing

For comparison, the same setup throwing InvalidOperationException leaves the task Faulted, and RethrowExceptions() throws as documented. Both results were confirmed with a temporary MSTest against main (f6424e3).

Suggested fix

Take either approach:

• In RethrowExceptions(), also handle PollingTask.IsCanceled and rethrow the action's original exception. The faulted ActionTask still holds it: ExceptionDispatchInfo.Capture(ActionTask.Exception!.GetBaseException()).Throw().
• Or stop an action failure from surfacing as cancellation. Have the loop catch the OperationCanceledException that TryRun rethrows and turn it into a fault, so PollingTask ends up Faulted.

Acceptance: add a regression test in which the action throws TaskCanceledException and RethrowExceptions() throws it.