fix: use undici.fetch instead of global fetch to match ProxyAgent version

Node.js v22.22.3 ships with built-in undici v6.24.1, which backs the global
fetch(). However, the project depends on undici v8.3.0 (via pnpm). The
ProxyAgent from undici v8.x requires handlers to implement onRequestStart,
but Node.js's built-in fetch handlers (from undici v6.x) do not have this
method. This version mismatch causes every proxied request to immediately
fail with 'invalid onRequestStart method', making the app appear
unresponsive to user input.

Fix: use undici's own fetch() (from the installed v8.x) instead of the
global fetch(), ensuring the fetch implementation version matches the
ProxyAgent version.

- anthropic.ts: pass undiciFetch to Anthropic SDK's fetch option
- openai-compat.ts: replace global fetch() with undiciFetch()

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

Author: root

packages/provider/src/anthropic.ts

@@ -7,7 +7,7 @@
 
 import Anthropic from '@anthropic-ai/sdk';
 import type { MessageParam, ContentBlockParam, TextBlockParam, Tool } from '@anthropic-ai/sdk/resources/messages.mjs';
-import { ProxyAgent } from 'undici';
+import { ProxyAgent, fetch as undiciFetch } from 'undici';
 
 import type { Message } from '@coder/shared';
 import type { ToolDefinition } from '@coder/shared';
@@ -46,6 +46,13 @@ export class AnthropicProvider implements Provider {
       baseURL: config.baseUrl,
       timeout: config.timeout ?? 300_000,
       maxRetries: 0, // We handle retries ourselves in withRetry()
+      // Use undici's own fetch to ensure compatibility between ProxyAgent
+      // and the underlying fetch implementation. Node.js's global fetch is
+      // backed by the built-in undici (v6.x), while ProxyAgent comes from
+      // the installed undici (v8.x). Version mismatches cause
+      // "invalid onRequestStart method" errors.
+      // eslint-disable-next-line @typescript-eslint/no-explicit-any
+      fetch: undiciFetch as any,
       ...(config.proxy ? { fetchOptions } : {}),
     });
   }

packages/provider/src/openai-compat.ts

@@ -16,7 +16,7 @@
 
 import type { Message } from '@coder/shared';
 import type { ToolDefinition } from '@coder/shared';
-import { ProxyAgent } from 'undici';
+import { ProxyAgent, fetch as undiciFetch } from 'undici';
 
 import type {
   Provider,
@@ -278,7 +278,12 @@ export class OpenAICompatProvider implements Provider {
       if (this.proxyAgent) {
         fetchInit.dispatcher = this.proxyAgent;
       }
-      const response = await fetch(url, fetchInit as RequestInit);
+      // Use undici's own fetch to ensure compatibility between ProxyAgent
+      // and the underlying fetch implementation. Node.js's global fetch is
+      // backed by the built-in undici (v6.x), while ProxyAgent comes from
+      // the installed undici (v8.x). Version mismatches cause
+      // "invalid onRequestStart method" errors.
+      const response = await undiciFetch(url, fetchInit as any);
 
       if (!response.ok) {
         const errorBody = await response.text().catch(() => '');