This is great. I like the idea of it just showing up in your editor, rather than having to go look for it (presuming you spend enough time in an editor, which is likely here). One step removed from a, "leave a note on the keyboard so I know they'll see it!" I was also trying a calendar.txt for a while and ended up overengineering my solution to the problem of wanting to have it available on multiple devices:
https://txtcal.app/ (naturally I haven't even added search yet, which was probably the reason I switched to a text calendar in the first place!)
I had posted a Show HN about it last night, so it was really cool to see another approach posted today.