It's is pretty cool, I can feel the energy poured into making your personal computing experience more seamless! Though the first thing I wondered when reading your examples is "how is ambiguity resolved?". Like albums, artists and tracks having the same string or sharing a prefix (search in this specific order, I guess?); or artists having the exact same name.

The aspect I like the most is using the filesystem as a database, since that's what UNIX people should like (and you can use symlinks for more complex cases). In fact, I myself made a music player with that as central philosophy, though it is much more bare/suckless compared to yours: https://git.sr.ht/~q3cpma/mus

Did you consider implementing a simple event system (maybe even IPC) for track and status change? Possibly MPRIS or something simpler. That was the main feature I kept from cmus when creating mus, so that I can easily interact with it through lemonbar and scripts.