test(ai): avoid leaking fetch stubs

packages/ai/test/azure-openai-responses-stream.test.ts

@@ -97,7 +97,7 @@ describe("azure openai responses streaming", () => {
 
 	it("sends an async onPayload replacement body", async () => {
 		let capturedBody: Record<string, unknown> | undefined;
-		global.fetch = vi.fn(async (_input: string | URL | Request, init?: RequestInit) => {
+		const fetchMock = vi.fn(async (_input: string | URL | Request, init?: RequestInit) => {
 			capturedBody = typeof init?.body === "string" ? (JSON.parse(init.body) as Record<string, unknown>) : undefined;
 			return createSseResponse([
 				{
@@ -113,13 +113,14 @@ describe("azure openai responses streaming", () => {
 					},
 				},
 			]);
-		}) as unknown as typeof fetch;
+		});
 
 		const result = await streamAzureOpenAIResponses(
 			azureModel,
 			{ messages: [{ role: "user", content: "Say hello", timestamp: Date.now() }] },
 			{
 				apiKey: "test-key",
+				fetch: fetchMock as unknown as typeof fetch,
 				azureBaseUrl: azureModel.baseUrl,
 				azureApiVersion: "v1",
 				onPayload: async payload => ({

packages/ai/test/openai-codex-stream.test.ts

@@ -299,16 +299,17 @@ describe("openai-codex streaming", () => {
 		const context = createCodexTestContext();
 		const model = { ...createCodexTestModel("https://chatgpt.com/backend-api"), preferWebsockets: false };
 		let capturedBody: Record<string, unknown> | undefined;
-		global.fetch = vi.fn(async (_input: string | URL, init?: RequestInit) => {
+		const fetchMock = vi.fn(async (_input: string | URL, init?: RequestInit) => {
 			capturedBody = typeof init?.body === "string" ? (JSON.parse(init.body) as Record<string, unknown>) : undefined;
 			return new Response(createCompletedCodexSse("Hello"), {
 				status: 200,
 				headers: { "content-type": "text/event-stream" },
 			});
-		}) as unknown as typeof fetch;
+		});
 
 		const result = await streamOpenAICodexResponses(model, context, {
 			apiKey: token,
+			fetch: fetchMock as unknown as typeof fetch,
 			onPayload: async payload => ({
 				...(payload as Record<string, unknown>),
 				input: [{ role: "user", content: [{ type: "input_text", text: "replacement" }] }],