Function passing not working?

I'm trying to do something sort of complicated on my site (basically work around #66) using the function passing capability, but it doesn't seem to be working for me. I simplified it down to a minimal form. I have this global data file cachetest.js:

import Fetch from "@11ty/eleventy-fetch"

export default async function() {
    return await Fetch(async () => {
        console.log("Cache miss")
        return {
            foo: "bar"
        }
    }, {
        requestId: "cachetest",
        duration: "1h"
    })
}

Each time I run it logs "Cache miss" to the shell output. Never does it seem to write anything to .cache. Have I done something wrong here?

Start with the minimal example in cachetest.js and the function-passing behavior exposed by @11ty/eleventy-fetch. Run it repeatedly while checking whether .cache is written and whether “Cache miss” appears each time. Done means the supplied function honors requestId and duration so repeated runs use the cached result.