And SQLite: https://sqlite.org/appfileformat.html
In fact, relevantly to this article: https://sqlite.org/affcase1.html
In fact, relevantly to this article: https://sqlite.org/affcase1.html
Zip is a known format, so library support is mature. It can contain a local file system. And no one is going to casually muck about in it, so you can trust the structure.