feat: message counting for chat sessions (#430)

open_notebook/utils/graph_utils.py

@@ -0,0 +1,18 @@
+from langchain_core.runnables import RunnableConfig
+from loguru import logger
+
+async def get_session_message_count(graph, session_id: str) -> int:
+    """Get message count from LangGraph state, returns 0 on error."""
+    try:
+        thread_state = await graph.aget_state( # async version
+            config=RunnableConfig(configurable={"thread_id": session_id})
+        )
+        if (
+            thread_state
+            and thread_state.values
+            and "messages" in thread_state.values
+        ):
+            return len(thread_state.values["messages"])
+    except Exception as e:
+        logger.warning(f"Could not fetch message count for session {session_id}: {e}")
+    return 0