Very similar effort https://latexy.web.app/ :)

Does this work on Firefox or Safari? You say “Firefox or Safari fall back to a virtual filesystem” but somehow I can’t get this fallback to work. When I click New Project I just get a reminder to use Chrome or Edge. Is there a button to press to trigger the fallback?

I love this use of wasm!

I never really got the hang of LaTeX but I've really enjoyed Typst the past few years and even made a few books with it. Have you ever tried that or have thought on it?

I copy-pasted a random LaTeX doc from many years ago (I made sure I wrote it before 2020 so it did not use any new features not in TeX Live 2020), and upon compilation I got the error

    Font OT1/cmr/m/n/10.95=cmr10 at 10.95pt not loadable: Bad metric (TFM) file.

on line 13017. The document had only 200 lines so this must be from a package. It was really not clear where the error was coming from. I guessed that it was coming from \usepackage{microtype}, so I commented it out, but the same error persisted.

I decided to hard refresh the tab and this time I got a different error:

    TeX capacity exceeded, sorry [text input levels=15].

on line 39. Again it was unclear line 39 of which package.

This is super cool. I wish there was something like this for ConTeXt too.

Anyone know if this includes TikZ?

Well done!