fix(core): Pair proxied AI fetches with their own undici (no-changelog) (#36318)

packages/@n8n/ai-utilities/src/__tests__/utils/http-proxy-agent.test.ts

@@ -1,4 +1,4 @@
-import { Agent, ProxyAgent } from 'undici';
+import { Agent, ProxyAgent, fetch as undiciFetch } from 'undici';
 import type { MockedFunction } from 'vitest';
 
 import { getNodeProxyAgent, getProxyAgent, proxyFetch } from 'src/utils/http-proxy-agent';
@@ -11,11 +11,9 @@ vi.mock('undici', () => ({
 	ProxyAgent: vi.fn(function (options) {
 		return { type: 'ProxyAgent', options };
 	}),
+	fetch: vi.fn(),
 }));
 
-// Mock global fetch
-global.fetch = vi.fn();
-
 describe('getProxyAgent', () => {
 	// Store original environment variables
 	const originalEnv = { ...process.env };
@@ -308,7 +306,7 @@ describe('getProxyAgent', () => {
 describe('proxyFetch', () => {
 	// Store original environment variables
 	const originalEnv = { ...process.env };
-	const mockFetch = global.fetch as MockedFunction<typeof fetch>;
+	const mockFetch = undiciFetch as unknown as MockedFunction<typeof fetch>;
 
 	// Reset environment variables and mocks before each test
 	beforeEach(() => {

packages/@n8n/ai-utilities/src/utils/http-proxy-agent.ts

@@ -21,7 +21,7 @@ import { createHttpsProxyAgent, resolveProxyUrl } from '@n8n/backend-network/pro
 import type { AgentOptions } from 'node:https';
 import type { LookupFunction } from 'node:net';
 /* eslint-disable n8n-local-rules/no-uncentralized-http -- langchain consumers pin undici v6, incompatible with backend-network's v7 dispatchers; see block comment below */
-import { Agent, ProxyAgent } from 'undici';
+import { Agent, ProxyAgent, fetch as undiciFetch } from 'undici';
 
 /**
  * Options for configuring HTTP agent timeouts.
@@ -113,11 +113,12 @@ export async function proxyFetch(
 	const targetUrl = input instanceof Request ? input.url : input.toString();
 	const dispatcher = getProxyAgent(targetUrl, timeoutOptions, lookup);
 
-	return await fetch(input, {
-		...init,
-		// @ts-expect-error - dispatcher is an undici-specific option not in standard fetch
+	// The dispatcher comes from this package's undici, so the request must use
+	// the same undici's fetch: the global fetch on Node >= 26 rejects it.
+	return (await undiciFetch(input as Parameters<typeof undiciFetch>[0], {
+		...(init as Parameters<typeof undiciFetch>[1]),
 		dispatcher,
-	});
+	})) as unknown as Response;
 }
 
 /**

packages/@n8n/nodes-langchain/nodes/llms/LMChatAnthropic/methods/__tests__/searchModels.test.ts

@@ -1,8 +1,13 @@
+import { proxyFetch } from '@n8n/ai-utilities';
 import type { ILoadOptionsFunctions } from 'n8n-workflow';
 import type { Mocked } from 'vitest';
 
 import { searchModels } from '../searchModels';
 
+vi.mock('@n8n/ai-utilities', () => ({
+	proxyFetch: vi.fn(),
+}));
+
 const mockModels = [
 	{
 		id: 'claude-3-opus-20240229',
@@ -51,11 +56,12 @@ describe('searchModels', () => {
 			json: async () => ({ data: mockModels }),
 			text: async () => '',
 		});
-		vi.stubGlobal('fetch', fetchSpy);
+		vi.mocked(proxyFetch).mockImplementation(
+			fetchSpy as unknown as typeof import('@n8n/ai-utilities')['proxyFetch'],
+		);
 	});
 
 	afterEach(() => {
-		vi.unstubAllGlobals();
 		vi.clearAllMocks();
 	});
 

packages/@n8n/nodes-langchain/nodes/llms/LMChatAnthropic/methods/searchModels.ts

@@ -1,4 +1,4 @@
-import { getProxyAgent } from '@n8n/ai-utilities';
+import { proxyFetch } from '@n8n/ai-utilities';
 import { listAnthropicModels } from '@n8n/ai-utilities/model-discovery';
 import type { ILoadOptionsFunctions, INodeListSearchResult } from 'n8n-workflow';
 
@@ -19,11 +19,7 @@ export async function searchModels(
 		apiKey: (credentials.apiKey as string) ?? '',
 		baseURL,
 		headers: mergeCustomHeaders(credentials, {}),
-		fetch: async (url, init) =>
-			await fetch(url, {
-				...init,
-				dispatcher: getProxyAgent(baseURL),
-			} as RequestInit),
+		fetch: proxyFetch,
 	});
 
 	return {

packages/@n8n/nodes-langchain/nodes/llms/LMChatOpenAi/methods/__tests__/loadModels.test.ts

@@ -1,8 +1,13 @@
+import { proxyFetch } from '@n8n/ai-utilities';
 import type { ILoadOptionsFunctions } from 'n8n-workflow';
 import type { Mocked } from 'vitest';
 
 import { searchModels } from '../loadModels';
 
+vi.mock('@n8n/ai-utilities', () => ({
+	proxyFetch: vi.fn(),
+}));
+
 const MODEL_IDS = [
 	'gpt-4',
 	'gpt-3.5-turbo',
@@ -43,7 +48,9 @@ describe('searchModels', () => {
 			json: async () => ({ data: MODEL_IDS.map((id) => ({ id })) }),
 			text: async () => '',
 		});
-		vi.stubGlobal('fetch', fetchSpy);
+		vi.mocked(proxyFetch).mockImplementation(
+			fetchSpy as unknown as typeof import('@n8n/ai-utilities')['proxyFetch'],
+		);
 	});
 
 	afterEach(() => {

packages/@n8n/nodes-langchain/nodes/llms/LMChatOpenAi/methods/loadModels.ts

@@ -1,4 +1,4 @@
-import { getProxyAgent } from '@n8n/ai-utilities';
+import { proxyFetch } from '@n8n/ai-utilities';
 import { listOpenAiModels } from '@n8n/ai-utilities/model-discovery';
 import { AiConfig } from '@n8n/config';
 import { Container } from '@n8n/di';
@@ -24,11 +24,7 @@ export async function searchModels(
 		apiKey: credentials.apiKey as string,
 		baseURL,
 		headers,
-		fetch: async (url, init) =>
-			await fetch(url, {
-				...init,
-				dispatcher: getProxyAgent(baseURL),
-			} as RequestInit),
+		fetch: proxyFetch,
 	});
 
 	return {

packages/@n8n/nodes-langchain/nodes/llms/test/LmChatAnthropic.test.ts

@@ -1,7 +1,12 @@
 /* eslint-disable n8n-nodes-base/node-filename-against-convention */
 /* eslint-disable @typescript-eslint/unbound-method */
 import { ChatAnthropic } from '@langchain/anthropic';
-import { N8nLlmTracing, makeN8nLlmFailedAttemptHandler, getProxyAgent } from '@n8n/ai-utilities';
+import {
+	N8nLlmTracing,
+	makeN8nLlmFailedAttemptHandler,
+	getProxyAgent,
+	proxyFetch,
+} from '@n8n/ai-utilities';
 import { createMockExecuteFunction } from 'n8n-nodes-base/test/nodes/Helpers';
 import type { ILoadOptionsFunctions, INode, ISupplyDataFunctions } from 'n8n-workflow';
 import type { Mock, Mocked } from 'vitest';
@@ -425,7 +430,9 @@ describe('LmChatAnthropic', () => {
 			beforeEach(() => {
 				mockGetCredentials = vi.fn();
 				fetchSpy = vi.fn();
-				vi.stubGlobal('fetch', fetchSpy);
+				vi.mocked(proxyFetch).mockImplementation(
+					fetchSpy as unknown as typeof import('@n8n/ai-utilities')['proxyFetch'],
+				);
 
 				mockLoadContext = {
 					getCredentials: mockGetCredentials,