This is seriously impressive, the schema-validated JSON/ASCII approach and seeded RNG are great foundations. Smart move keeping the gameplay logic separate from Three.js too, must make testing way less painful. Any particular pain point that pushed you toward that separation?
Anyway, I'm a composer, atmospheric/adaptive stuff mostly, happy to help on the audio side if you want to explore it, no pressure on payment given where things are at, I love this type of game so it would be a pleasure figuring it out.
If you want a reference point, here's some recent work:
https://x.com/ph4rosound/status/2064733056703799623
https://x.com/ph4rosound/status/2039254947716292906
I have also shipped 2 game jams here on Itch but given the short time frame of Jams(around a week) I am not 100% thrilled with the results though.