langchain - 💡(How to fix) Fix I want `@tool` defined tool available to return multimodal data

Submission checklist

• This is a feature request, not a bug report or usage question.
• I added a clear and descriptive title that summarizes the feature request.
• I used the GitHub search to find a similar feature request and didn't find it.
• I checked the LangChain documentation and API reference to see if this feature already exists.
• This is not related to the langchain-community package.

Package (Required)

• langchain
• langchain-openai
• langchain-anthropic
• langchain-classic
• langchain-core
• langchain-model-profiles
• langchain-tests
• langchain-text-splitters
• langchain-chroma
• langchain-deepseek
• langchain-exa
• langchain-fireworks
• langchain-groq
• langchain-huggingface
• langchain-mistralai
• langchain-nomic
• langchain-ollama
• langchain-openrouter
• langchain-perplexity
• langchain-qdrant
• langchain-xai
• Other / not sure / general

Feature Description

I want @tool defined tool function able to return multimodal data such as images.

I know I can implement this as a Tool Node and create a LangGraph, but making a graph for this is very tiring (as everyone knows)

I just want to give the agent an image fetching tool and let it run by client.bind_tools(image_fetching_tool).invoke()

The current @tool defined function only accepts raw str and dict which both will converted into just a str I wish there can be File schema that if you used it as return value, a ToolMessage instance with the file data written will be appended on the messages

Use Case

• Easier and quicker RAG tool implementation with returning images or PDFs

Proposed Solution

1. Add File class with constructor

File(
  file_type: literal,
  data: bytes,
  mime_type
)

1. If the user defined

@tool
def image_fetcher():
   ...
   return File("image", BINARY, "image/png")

1. The library adds

ToolMessage(
    content={
        "type": "image",
        "source_type": "base64",
        "data": BASE64_CONVERTED_DATA,
        "mime_type": "image/png",
    },
    tool_call_id=tool_call_id,
    name=name,
)

on the messages

Alternatives Considered

No response

Additional Context

No response