The new Haddock quickjump functionality doesn't work for documentation candidates.

When pressing 's' to open the quickjump for candidate documentations I get the following error:

```Failed to load file 'doc-index.json' containing definitions in this package.```

Start by reproducing the quickjump for candidate documentations with the 's' key and tracing where it loads doc-index.json. Inspect the code that generates or loads this file; done means documentation candidates open in quickjump without the missing-file error.

Written by the indexing model from the issue text.