Initial Checks

• I confirm that I'm using the latest version of Pydantic AI
• I confirm that I searched for my issue in https://github.com/pydantic/pydantic-ai/issues before opening this issue

Description

I'm testing out a simple temporal agent with a fetch MCP server. The agent attempted to fetch a webpage that doesn't exist, so it gets a 404. This is going to be fairly standard. The MCP server raises a ModelRetry exception, again fairly standard... but unfortunately, Temporal sees this as a failure of the activity and will now constantly retry this forever. ModelRetry exceptions should be considered non-retryable errors by default by Pydantic's Temporal agent.

Example Code

simply adding 


    toolsets=[
        MCPServerStdio(id="fetch", command="uvx", args=["mcp-server-fetch"])
    ],


to the agent in the example on the pydantic docs page https://ai.pydantic.dev/durable_execution/temporal/  you can reproduce this if you get it to hit a 404 page.

Python, Pydantic AI & LLM client version

python: 3.13.6
pydantic-ai: v1.8.0
LLM client: pydantic-ai-slim[openai] (open ai compatible custom API, using anthropic claude 3.7 as the model).