Add missing edge from start to "assistant"

agents.py

@@ -208,6 +208,7 @@ def build_graph(provider: str = "rwkv"):
     builder = StateGraph(MessagesState)
     builder.add_node("assistant", assistant)
     builder.add_node("tools", ToolNode(tools))
+    builder.add_edge(START, "assistant")
     builder.add_conditional_edges(
         "assistant",
         tools_condition,