next/headers are not printable on the server via console.log

### Link to the code that reproduces this issue https://github.com/ShogunPanda/next-headers-inspect-bug ### To Reproduce 1. Start the application in dev mode. 2. Create a page like the following one: ````js import { headers } from "next/headers"; export default async function Home() { "use server"; console.log(await headers()); return <h1>Hello world!</h1>; } ```` ### Current vs. Expected behavior The browser shows the following: ``` Unhandled Runtime Error Error: Cannot read private member #headersList from an object whose class did not declare it ``` This was also reported in https://github.com/vercel/next.js/discussions/68849. The stacktrace is pretty similar and the problem is in `Headers[Symbol.for('nodejs.util.inspect.custom')]`, which is defined in https://github.com/nodejs/undici/blob/main/lib/web/fetch/headers.js#L627. I tried to follow the code and saw the return of `await headers()` is ultimately an instance of `HeadersAdapter` (which extends `Headers`). This class cannot access the superclass `#headersList` and thus the exception. I tried to send a PR but got lost somewhere in the code as there must be some proxy object in the middle. Let me know if I can help. ### Provide environment information ```bash Operating System: Platform: darwin Arch: arm64 Version: Darwin Kernel Version 24.3.0: Thu Jan 2 20:24:23 PST 2025; root:xnu-11215.81.4~3/RELEASE_ARM64_T6020 Available memory (MB): 65536 Available CPU cores: 12 Binaries: Node: 22.14.0 npm: 10.9.2 Yarn: 1.22.21 pnpm: 9.4.0 Relevant Packages: next: 15.2.1 // There is a newer version (15.2.2) available, upgrade recommended! eslint-config-next: N/A react: 19.0.0 react-dom: 19.0.0 typescript: N/A ``` ### Which area(s) are affected? (Select all that apply) Headers ### Which stage(s) are affected? (Select all that apply) next dev (local), next start (local) ### Additional context This happens on both Next 14 or Next 15.