Fail if user provides mcp servers

Author: tconley1428

temporalio/contrib/openai_agents/_openai_runner.py

@@ -51,6 +51,11 @@ async def run(
                     "Provided tool is not a tool type. If using an activity, make sure to wrap it with openai_agents.workflow.activity_as_tool."
                 )
 
+        if len(starting_agent.mcp_servers) > 0:
+            raise ValueError(
+                "Temporal OpenAI agent does not support on demand MCP servers."
+            )
+
         context = kwargs.get("context")
         max_turns = kwargs.get("max_turns", DEFAULT_MAX_TURNS)
         hooks = kwargs.get("hooks")