Reference-style links don't work in keypoints

I appreciate this probably isn't a common use case, but if you try to link in a keypoint like this:

```
[link text][link-reference]
```

with this elsewhere in the markdown file,
```
[link-reference]: https://www.thelink.com
```
it doesn't render as a link. You just see the markdown.

However if you use an inline link it works, but you end up with repetition in your markdown file:
```
[link-text](https://www.thelink.com)
```

Reproduce the issue in a lesson markdown file using the keypoint reference-style link and the separate link definition shown here, then compare it with the working inline link. Trace the lesson template's markdown rendering path and verify that the reference-style link renders as a link without repetition.

Written by the indexing model from the issue text.