Can't import json files

[futuraprime]

Hi folks, I've hit a problem where I can't get Snowpack/svelte to build with json imports.

I've set up a minimal version of my build template here: https://github.com/futuraprime/json-test. This will run dev fine, but as soon as I try to build, it fails (it can't find any of the json files):

[@snowpack/plugin-optimize]  could not locate "/test.json"
[@snowpack/plugin-optimize]  could not locate "/test.json"
...voluminous webpack errors follow...

What's wrong with my config? Why can't I import json files?

EDIT: Having experimented a little more, it looks like turning off Snowpack's bundler in the snowpack config fixes the issue. Since we're using webpack to bundle, this is ok for us, but it'd be frustrating if we weren't using Webpack.