fix: bundle config/recursion/missing-key fixes

- dataflows/config: deepcopy + one-level dict merge so a partial
  set_config doesn't clobber sibling defaults
- graph: thread max_recur_limit from config to Propagator
- openai_client: name the missing env var in the API-key error

#788 #764 #680

tradingagents/llm_clients/openai_client.py

@@ -162,6 +162,12 @@ class OpenAIClient(BaseLLMClient):
                 api_key = os.environ.get(api_key_env)
                 if api_key:
                     llm_kwargs["api_key"] = api_key
+                else:
+                    raise ValueError(
+                        f"API key for provider '{self.provider}' is not set. "
+                        f"Please set the {api_key_env} environment variable "
+                        f"(e.g. add {api_key_env}=your_key to your .env file)."
+                    )
             else:
                 llm_kwargs["api_key"] = "ollama"
         elif self.base_url: