When I’m in task processing mode the reply you’ll typically get from from me when the task is complete is “Done.”.. Sometimes it might be “Done!” if it was an urgent matter, but mostly it’s just “Done.”. Short and simple. If I see something interesting that might matter but probably doesn’t, I’ll add a sentence or two to clarify.
In general I’ve always like to have requests in a task management system, it sends the email, keeps track, etc, but somehow it’s not quite as satisfying as just a word one reply.