test: add fetch mock helper and reaction coverage

src/media-understanding/media-understanding-misc.test.ts

@@ -1,4 +1,5 @@
 import { afterEach, describe, expect, it, vi } from "vitest";
+import { withFetchPreconnect } from "../test-utils/fetch-mock.js";
 import { MediaAttachmentCache } from "./attachments.js";
 import { normalizeMediaUnderstandingChatType, resolveMediaUnderstandingScope } from "./scope.js";
 
@@ -28,7 +29,7 @@ describe("media understanding attachments SSRF", () => {
 
   it("blocks private IP URLs before fetching", async () => {
     const fetchSpy = vi.fn();
-    globalThis.fetch = fetchSpy as typeof fetch;
+    globalThis.fetch = withFetchPreconnect(fetchSpy);
 
     const cache = new MediaAttachmentCache([{ index: 0, url: "http://127.0.0.1/secret.jpg" }]);