add timeout for client connection to prevent infinite hang

Author: mattzcarey

packages/agents/src/mcp/client-connection.ts

@@ -74,6 +74,13 @@ export type MCPTransportOptions = (
 ) & {
   authProvider?: AgentsOAuthProvider;
   type?: TransportType;
+  /**
+   * Connection timeout in milliseconds. Default: 15000 (15 seconds).
+   * If the connection doesn't complete within this time, it will fail.
+   * Timeouts are often caused by proxies (like Cloudflare WARP) that strip
+   * SSE newline terminators, causing the EventSource parser to hang.
+   */
+  connectionTimeoutMs?: number;
 };
 
 export type MCPClientConnectionResult = {
@@ -616,6 +623,8 @@ export class MCPClientConnection {
   ): Promise<MCPClientConnectionResult> {
     const transports: BaseTransportType[] =
       transportType === "auto" ? ["streamable-http", "sse"] : [transportType];
+    const connectionTimeoutMs =
+      this.options.transport?.connectionTimeoutMs ?? 15000;
 
     for (const currentTransportType of transports) {
       const isLastTransport =
@@ -628,7 +637,21 @@ export class MCPClientConnection {
       const transport = this.getTransport(currentTransportType);
 
       try {
-        await this.client.connect(transport);
+        // Timeouts are often caused by proxies (like Cloudflare WARP) that strip
+        // SSE newline terminators (\n\n), causing the EventSource parser to hang
+        // waiting for message boundaries that never arrive.
+        await Promise.race([
+          this.client.connect(transport),
+          new Promise<never>((_, reject) =>
+            setTimeout(
+              () =>
+                reject(
+                  new Error(`Connection timeout after ${connectionTimeoutMs}ms`)
+                ),
+              connectionTimeoutMs
+            )
+          )
+        ]);
 
         return {
           state: MCPConnectionState.CONNECTED,