Disclaimer: this might be a stupid suggestion ;)

Most (all?) other js files in this project (except routes) define a Constructor and return that. Here may be silly since there's no instances, but one thing I like is that it makes it easier (for me) to know what functions are "public" vs "private" at the function definition vs where the export is defined. I'd style it like this:

```js
function Bundle() {}

Bundle.bundle = function () {}
Bundle.unbundle = function () {}

function deriveBundleKeys() {}
//... etc
return Bundle
```

Its just a personal style thing I noticed, I'm happy either way, since it works :)