Why does ToolMessage in langgraph-sdk not include artifact like @langchain/core?

[vikram-typeset]

Hi LangGraph team,

I'm working on a project where I'm using the useStream hook from the LangGraph Cloud guide ([link](https://langchain-ai.github.io/langgraph/cloud/how-tos/use_stream_react/)) to connect a React frontend with a backend that streams LangGraph events.

From the backend, I'm setting an artifact in ToolMessage objects, which works fine when using @langchain/core. Here's a simplified example:

import { ToolMessage as ToolMessageCore } from '@langchain/core/messages';

const toolMessageCore: ToolMessageCore = new ToolMessageCore({
  content: 'Hello, world!',
  id: '123',
  tool_call_id: '123',
  name: 'tool_name',
  status: 'success',
  artifact: 'Artifact from tool',
});

However, the ToolMessage type from @langchain/langgraph-sdk doesn’t appear to support artifact:

import { ToolMessage as ToolMessageLanggraph } from '@langchain/langgraph-sdk';

const toolMessageLanggraph: ToolMessageLanggraph = {
  type: 'tool',
  content: 'Hello, world!',
  tool_call_id: '123',
  name: 'tool_name',
  status: 'success',
  artifact: 'Artifact from tool', // ❌ TypeScript error: artifact does not exist
};

This causes issues on the frontend because the useStream hook expects LangGraph's message format, and so I can't access the artifact that I know was generated by the tool.

Questions:

1. Is the omission of artifact in @langchain/langgraph-sdk's ToolMessage intentional?
2. If not, could it be added to align with @langchain/core?
3. Is there a recommended way to include and access tool artifacts when using useStream with LangGraph Cloud?

Thanks for your great work!