Update agent.py

agent.py

@@ -126,7 +126,9 @@ with open("system_prompt.txt","r",encoding="utf-8") as f:
 # 2) Build your graph
 def build_graph(provider: str = "huggingface") -> Graph:
     # 2a) Instantiate your LLM endpoint
-    api_token = os.environ["HF_API_TOKEN"]
+    api_token = os.getenv("HF_API_TOKEN")
+        if not api_token:
+            raise ValueError("HF_API_TOKEN not found: please add it under Settings → Secrets and variables in your Space")
     llm = LLM(provider=provider, token=api_token,  model="meta-llama/Llama-2-7b-chat-hf")
 
     # 2b) Attach tools