idx() inside an async function throws "must be an arrow function"

idx() inside an async function throws "must be an arrow function": a task in MiMo-V2.6-RL-harbor-code: MiMo-V2.6-RL Code (Harbor) (Harbor dataset). I'm using babel-plugin-idx together with babel-preset-env in my build. With the browser targets I care about, preset-env ends up downcompiling async /…