the software i'm using by the way is PC-BASIC which i found out about yesterday
it's a modern recreation of GW-BASIC, BASICA et al, simulating many video modes including Hercules and even Tandy 3-channel sound
https://robhagemans.github.io/pcbasic/
the book targets C64, TRS-80, Spectrum and Apple, so we'll find out what bugs arise and need to be fixed only once i'm done typing and try to run it
after fixing a couple more typos, it seems the game is playable
but i'm rubbish at it 😅
i'll take a break for today, i've taken down notes on what i found interesting about this experience to write a blog post on later