Defer gives an error when running in edge mode in a Next.js app on Vercel

[pangolingo]

I'm attempting to run a Defer function in a Route Handler (formerly called API Route) in my Nextjs app. For performance reasons I marked this API function as using the "edge" runtime instead of the default "nodejs" runtime. This results in an error when I run the function.

Expected behavior: There are no errors when running a Defer function on the edge runtime.

Actual behavior: I see an error when running the Defer function. This error occurs in the Next.js app, and the function is never run on Defer's side.

Error: invalid request body: function_name is missing or empty
    at (node_modules/@defer/client/esm/httpClient.js:83:18)
    at (src/app/api/background-job/route.ts:7:17)
    at (node_modules/next/dist/esm/server/future/route-modules/app-route/module.js:189:36) {
  code: 'bad_request'
}

Workarounds: If I change the route back to using the Node.js runtime, it runs without errors

Observations: The error message appears to indicate that Defer isn't able to figure out the function's name.

Docs for the edge runtime: https://nextjs.org/docs/app/building-your-application/routing/route-handlers#edge-and-nodejs-runtimes https://nextjs.org/docs/app/building-your-application/rendering/edge-and-nodejs-runtimes

Code sample: This is the Next.js route file - it's pretty simple:

import helloWorld from "@/defer/helloWorld";

export const dynamic = "force-dynamic"; // defaults to auto
export const runtime = "edge"; // 'nodejs' is the default

export async function POST(request: Request) {
  const result = await helloWorld("Dave");

  console.log("result", result);

  return new Response(JSON.stringify({ result }), {
    headers: { "Content-Type": "application/json" },
  });
}