Seconded. The way I look at this is to always build the allowable action space from nothing, and default to nothing. Most of the time it involves a state machine where each node comes with a white list of currently allowable verbs a client can send.

The alternative is an infinite action soup, which opens opportunities for inspiration by lateral thinking. I'm doing it this way for a single player Lovecraftian text editor I'm working on. It's a terrible idea for multiplayer things.