I made one of these years ago, much less polished but broadly similar

Wow - indeed. I see you made something like this already back in 2012. Impressive: https://github.com/Lerc/notanos That is more than 13 years ago when websockets where about to become generally available. Impressive! Don't be discouraged by people that argue what you should or should not do. The world is full with people with their own agenda or that simply have a too narrow view of how their world should operate.

To everyone: Ignore the nay-sayers. You've done more than most of them ever attempted. It's more easily said than done, negative feedback tends to set off a stronger emotional response. Seek feedback from people you know will support you. I play guitar, for fun. I've once posted a recording. Someone said something mean. It really hurt me somehow, I didn't record anything at all in the following 15 years. Recently I've been talking a lot with my sister, we both really liked a song so we agreed to record a cover. I've now been working on that for many evenings. I'm sharing the WIP demos with people I know will give me constructive feedback. I keep going. It's more work than I've expected! But it's so much fun. Don't stop dreaming.

Notanos looks awesome, I will check it out. There are several milestones of my project that will likely require forks in the road where I might have to do a rewrite, but I hope to be able to keep doing it and learning. I think that in 10-20 years with the progress of AI, this project could become something quite amazing, but by then maybe everything will be amazing by todays standards.