Bug Description

When using ChatYandexGPT with agents that require multiple iterations (maxIterations > 1), a TypeError occurs during AIMessage construction:

TypeError: Cannot read properties of undefined (reading 'additional_kwargs')

The error occurs at line 30 in the AIMessage constructor:

const rawToolCalls = initParams.additional_kwargs?.tool_calls;

Environment

• Package: @langchain/yandex version 0.1.0
• Core: @langchain/core version 0.3.73
• LangChain: langchain version 0.3.32
• Platform: macOS X 15.6.1, MacBook M1

Steps to Reproduce

1. Initialize ChatYandexGPT model:

export const llm = new ChatYandexGPT({
  temperature: 0,
  apiKey: "...",
  folderID: "...",
  model: 'yandexgpt',
});

2. Create an agent with tools:

import { ChatYandexGPT } from "@langchain/yandex";
import { AgentExecutor, createToolCallingAgent } from "langchain/agents";
import { RequestsGetTool } from "langchain/tools";

const tools = [new RequestsGetTool()];
const agent = await createOpenAIFunctionsAgent({
   llm: llm,
   tools: tools,
   prompt: ChatPromptTemplate.fromMessages([
     new SystemMessage('You are an API assistant...'),
     new HumanMessage('{input}'),
     ['placeholder', '{agent_scratchpad}'],
   ]),
   streamRunnable: true,
});

const agentExecutor = new AgentExecutor({
  agent,
  tools,
  maxIterations: 3, // Error occurs when > 1
});

3. Execute any query that requires tool usage:

await agentExecutor.invoke({ input: "Make an HTTP request hello" });

Expected Behavior

The agent should execute successfully with multiple iterations, properly handling tool calls and creating AIMessage instances with correctly initialized additional_kwargs.

Actual Behavior

The execution fails with a TypeError when the agent attempts to create AIMessage instances during subsequent iterations, specifically when trying to access additional_kwargs.tool_calls.

Root Cause Analysis

The issue appears to be in the ChatYandexGPT._generate() method implementation. When creating AIMessage instances, the method is not properly initializing the additional_kwargs parameter, causing it to be undefined when the AIMessage constructor tries to access it.

Suggested Fix

The ChatYandexGPT._generate() method should ensure that additional_kwargs is always provided when creating AIMessage instances:

// Current (problematic) implementation likely:
return new AIMessage(response.content);

// Should be:
return new AIMessage({
  content: response.content,
  additional_kwargs: response.additional_kwargs || {}
});

Additional Context

• The error only occurs when maxIterations > 1, suggesting it's related to tool calling in multi-step agent execution
• Other chat models (ChatOpenAI, ChatAnthropic, etc.) work correctly with the same setup
• The issue is specific to the JavaScript/TypeScript implementation of ChatYandexGPT

Related Issues

This appears to be related to issue #32814 in the main langchain repository, but the actual fix needs to be implemented in the langchain-community package.