They also weren't supposed to be leaking the code itself either. I don't know enough about JS tooling, but is it possible that this might just be the pre-stripped version?

That’s what a source map is. It’s included in debug builds so that browser debuggers (and others) can step through the original code, comments and all, instead of the compiled javascript (which back in the day could become an undecipherable mess of callbacks if you were transpiling async/await to the legacy Promise API).

Unfortunately in many bundlers making a mistake like this is as easy as an agent deleting “process.env[‘ENV’] === ‘debug’” which they’ll gladly do if you point them at a production or staging environment and ask them to debug the stripped/compiled/minified code.