fix: standardize error message to 'INTERNAL_ERROR' in MCPProtocol

Author: jskorlol

src/Protocol/MCPProtocol.php

@@ -138,7 +138,7 @@ public function handleMessage(string $clientId, array $message): ProcessMessageD
 
             $jsonErrorResource = new JsonRpcErrorResource(
                 exception: new JsonRpcErrorException(
-                    message: $e->getMessage() ?: 'INTERNAL_ERROR',
+                    message: 'INTERNAL_ERROR',
                     code: JsonRpcErrorCode::INTERNAL_ERROR,
                     data: [
                         'exception' => $e::class,