Adding an `onRequest` interceptor to ofetch instance causes `registerEndpoint` to not be reached

[MikeBellika]

Environment

• Operating System: Darwin
• Node Version: v22.17.0
• Nuxt Version: 4.1.0
• CLI Version: 3.28.0
• Nitro Version: 2.12.5
• Package Manager: pnpm@9.15.4
• Builder: -
• User Config: compatibilityDate, devtools, modules
• Runtime Modules: @nuxt/test-utils@3.19.2
• Build Modules: -

Reproduction

https://github.com/MikeBellika/nuxt-test-utils-ofetch-repro

pnpm i && pnpm test

Describe the bug

Using an ofetch instance with an onRequest interceptor prevents registerEndpoint from being called.

<script setup lang="ts">
async function fetcher() {
  const fetcher = $fetch.create({});
  await fetcher("/test/");
}
async function customFetcher() {
  const fetcher = $fetch.create({
    onRequest() {},
  });
  await fetcher("/test/");
}
</script>
<template>
  <div>
    <button data-testid="normal-fetcher" @click="fetcher">fetch</button>
    <button data-testid="custom-fetcher" @click="customFetcher">fetch</button>
  </div>
</template>

import { mountSuspended, registerEndpoint } from "@nuxt/test-utils/runtime";
import { it, expect, vi } from "vitest";
import app from "../../app/app.vue";

it("/test/ called without onRequest intercepted", async () => {
  // ✅ This test passes. It clicks the button that uses a fetcher without `onRequest`
  const endpoint = vi.fn(() => "hello");
  registerEndpoint("/test/", () => endpoint());
  const component = await mountSuspended(app);
  component
    .find<HTMLButtonElement>('[data-testid="normal-fetcher"]')
    .element.click();
  expect(endpoint).toHaveBeenCalled();
  component.unmount();
});

it("/test/ called WITH onRequest intercepted", async () => {
  // ❌ This test fails. Calls the fetcher that has a custom `onRequest`
  const endpoint = vi.fn(() => "hello");
  registerEndpoint("/test/", () => endpoint());
  const component = await mountSuspended(app);
  component
    .find<HTMLButtonElement>('[data-testid="custom-fetcher"]')
    .element.click();
  expect(endpoint).toHaveBeenCalled();
  component.unmount();
});

Additional context

Probably related to #798

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