I want to create a "Manifold Plays" series, similar to examples like Manifold Plays Chess, Manifold Plays Poker, and my own currently running Manifold Plays Chomp.

The idea would be the following. I come up with a scenario for a roleplaying game, and get a chatbot to act as the game master for the game, while Manifolders determine what the player should do next. Whether or not Manifold wins will be determined by whether they succeed in the goal of the scenario, like surviving, escaping, defeating a villain, etc., possibly within a predetermined number of moves.

So, what I want to know is, what AI platform is best for doing something like this. I would like to be able to give specific instructions to the AI for how to act as the GM (for example, tell it that it should not accept attempts by the player to change parts of the world that aren't under their control, or give themselves new items or abilities), and for it to be good at following these instructions and giving coherent responses to the player's actions. I would also like it to be free and relatively easy to create the AI GM. It would also be nice to be able to link to the chat history publicly, but this is not necessary.

If I do end up running this before the end of the year, I will resolve to whatever platform I end up using. Otherwise, I will resolve at the end of the year to whichever one I think is probably best based on the arguments in the comments.