fix(protocol): abort active request handlers on connection close

- Track request handlers with AbortControllers in _requestHandlerAbortControllers
- Abort all active request handlers in _onclose() to prevent hanging operations
- Ensure both outgoing requests (response handlers) and incoming requests (request handlers) are properly terminated

Fixes issue where request handlers would continue running after connection
closure, causing timeouts and resource leaks.

Author: alasano

src/shared/protocol.ts

@@ -334,12 +334,24 @@ export abstract class Protocol<
     this._progressHandlers.clear();
     this._pendingDebouncedNotifications.clear();
     this._transport = undefined;
+    
+    // Abort all active request handlers
+    const requestHandlerAbortControllers = this._requestHandlerAbortControllers;
+    this._requestHandlerAbortControllers = new Map();
+    
     this.onclose?.();
 
     const error = new McpError(ErrorCode.ConnectionClosed, "Connection closed");
+    
+    // Reject all pending response handlers (for outgoing requests)
     for (const handler of responseHandlers.values()) {
       handler(error);
     }
+    
+    // Abort all active request handlers (for incoming requests being processed)
+    for (const abortController of requestHandlerAbortControllers.values()) {
+      abortController.abort(error);
+    }
   }
 
   private _onerror(error: Error): void {