This is a really interesting idea, I'd be interested to see it fleshed out in a post jam version (the absolute ideal would be and AR game, but that would be a very expensive gamble).
One way you could extend the mastermind game would be to have lower-numbered nodes be easier (with fewer digits, fewer symbols or more guesses). Because you can try again, you currently have unlimited guesses, so it might be interesting to lock players out of a code once they fail it (and then taking a high number would be a big deal. Additionally, you could prevent players from attempting a node unless their team holds an adjacent node. That would make holding on to some near the center super important and might develop into a strategy layer.
Thanks for your game, it gave me lots to think about :) If you're interested in a different mastermind variant, check out my team's game!