I wrote it via this script, which picks progressions, then modes, and fills them out with riffs and lead phrases that fit those modes. (I tried out sometimes doing some Slayer-style chaos soloing, but I learned you need a human to do that. Or better programming.) It took way longer to get working than I expected, derailing my Synthruary a bit.
Once I had the midi files generated to my liking, I put them in NanoStudio with guitar and bass virtual instruments on them. Even though I know all synths that try to sound like guitars with distortion are terrible, I gave them a shot.
Then, it occurred to me that clean guitar synths are OK, and I could use renderings with those synths as direct input to an amp modeler. It worked! It doesn't sound totally human (but I could get closer with some changes), but I now have a way of making generative guitar music.