I'm designing an application to handle requests from users. Requests will be assigned to all kinds of people. For instance, a "Request for vacations" would be handled by someone in HR. But a request to repair a door lock would be handled by someone in facilities management. In some complex cases, multiple people could work on a single request.
I'm looking for a noun to describe someone who works on requests.
A general term that means "someone who does something in a process" would be fine too.