What's the correct way to handle dead-letter queue

[tryffel]

Hi,

it would be helpful to have functionality for dead-letter queue.
Example use case would be to retry task N times and after that, run specific callback to handle permanent failure in application logic.
Now this is not possible since the task handler doesn't have visibility into task's failure count.

A good way to handle this could be either to have separate deadletterqueue-handler similar to existing error handler that is called before moving the task into archive: TaskArchived(task).
Alternatively, call the same task handler, but expose the retry count / state transition info into task type so that the handler can handle the case with e.g. if task.IsArchived().