DocumentUrl in message_history is missing "_media_type" #2394
Description
Initial Checks
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Description
Hey Hey,
so this might be a bit special but I am trying to use a mcp client, that when given a pdf document I want it to do mcp stuff (create, update, delete entities on the server). In case information is lacking I want the client to be able to "chat" with the server(user who via frontend interacts with server) and so I am sending the history to the server and back to the client on every interaction. But it crashes with
AttributeError: 'DocumentUrl' object has no attribute '_media_type'. Did you mean: 'media_type'?
But this only happens when I use the history. I did some very crude hardcoded test to see what happens if I were to add the _media_type from the document. And this would work.
So I am wondering is message_history with a document in the loop bugged or am I simply doing it wrong?
Example Code
MCP agent is a MCPServerStreamableHTTPClient similar to the doc
CodeSnippet problematic part:
try:
async with mcp_agent:
history = []
if request.history:
history = (
ModelMessagesTypeAdapter.validate_python(request.history) or []
)
if request.documentUrl:
docUrl = DocumentUrl(url=request.documentUrl)
agent_request = (
[request.prompt, docUrl] if request.documentUrl else [request.prompt]
)
copyOfHistory = history.copy()
if copyOfHistory:
copyOfHistory[0].parts[0].content[1]._media_type = docUrl.media_type <<< this works (obviously only for the first time)
result = await mcp_agent.run(
agent_request,
message_history=history,
)
raw_messages = result.all_messages()
messages = to_jsonable_python(raw_messages)
output = result.output
return McpResponse(output=output, messages=messages)
except Exception as e:
logger.error(f"Error in MCP client: {str(e)}", exc_info=True)
raise ePython, Pydantic AI & LLM client version
Python 3.13.3
pydantic-ai-slim[mcp] 0.4.10
LLM gemini-flash-2.5 (via vertex ai)