Each agent gets to do one thing once.
If the rules had just said, "Each agent can only use one ability per season," a rules lawyer would say that the agent could use that one ability an infinite number of times (e.g., with the aforementioned "take two noble actions" effect).
Thanks for the quick response. Glad to hear were playing correctly. Only played once so far but enjoyed the game - surprised it's not rated higher on BGG.