I've started making most of my prototypes single HTML documents with inline CSS and JavaScript, because a single file is a lot easier to store somewhere and share and will probably keep on working forever (browsers are really good at backwards compatibility).
I chuck some of them on my public tools.simonwillison.net collection, others in their own GitHub repos with GitHub Pages enabled, and some I just share in a Gist (served via gisthost.github.io) or stick in a public S3 bucket so I have a URL for them.
If a prototype is against an existing project sometimes I'll leave it to silently rot in a branch on GitHub.
The single file is interesting, we’ve been observing something similar too. Do you have a specific prompt that you load in by default to make this work? Are these react files, or just pure HTML/JS/CSS? Aka do you compile it via Esbuild or webpack or something, or are you asking the model to generate something that works out of the box?
We’ve been seeing Claude artifacts sometimes come out as JSX or TSX