fix(h2-transport): address review nits (unreachable 101, url descriptor, stale comment)

Per review on #815:

- Drop `101` from NULL_BODY_STATUSES — Switching Protocols is an HTTP/1.1
  upgrade status and can't occur over HTTP/2, so it was unreachable.
- Add `writable: true` to the `Response.url` property descriptor.
- Fix a stale comment in tests/index.test.ts that referenced the pre-refactor
  `useHttp2` / `makeHttp2Fetch(...)` shape; it's now `resolveHttp2Fetch(options)`.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: Reflex

src/lib/h2-transport/index.ts

@@ -23,8 +23,9 @@ import { Response } from 'node-fetch';
 import { type Fetch } from '../../core';
 
 // Statuses that must not carry a body per the Fetch spec; node-fetch's Response
-// rejects a non-null body for these.
-const NULL_BODY_STATUSES = new Set([101, 204, 205, 304]);
+// rejects a non-null body for these. (101 is an HTTP/1.1 upgrade status and can't
+// occur over HTTP/2, so it's omitted.)
+const NULL_BODY_STATUSES = new Set([204, 205, 304]);
 
 const MIN_NODE_MAJOR = 18;
 
@@ -84,7 +85,7 @@ function toFetchResponse(h2: H2Response): Response {
 
   // node-fetch derives `url` from the request internals it never saw; expose the
   // real request URL (`Response.url` is a prototype getter, shadowed here).
-  Object.defineProperty(response, 'url', { value: h2.url, configurable: true });
+  Object.defineProperty(response, 'url', { value: h2.url, writable: true, configurable: true });
   return response;
 }
 

tests/index.test.ts

@@ -100,7 +100,7 @@ describe('instantiate client', () => {
   test('custom fetch wins over http2', async () => {
     // When both `fetch` and `http2` are provided, the custom fetch must be used —
     // the h2 adapter should not run. Locks in src/index.ts:
-    //   fetch: options.fetch ?? (useHttp2 ? makeHttp2Fetch(...) : undefined)
+    //   fetch: options.fetch ?? resolveHttp2Fetch(options)
     const customFetch = jest.fn((url: RequestInfo) =>
       Promise.resolve(
         new Response(JSON.stringify({ url, custom: true }), {