feat(chat): Implement real-time SSE streaming with reasoning steps and improved UI indicators.

backend/src/ea_chatbot/api/routers/agent.py

@@ -11,7 +11,7 @@ from ea_chatbot.history.models import User as UserDB, Conversation
 from ea_chatbot.api.schemas import ChatRequest
 import io
 import base64
-from langchain_core.messages import BaseMessage
+from langchain_core.runnables.config import RunnableConfig
 
 router = APIRouter(prefix="/chat", tags=["agent"])
 
@@ -39,7 +39,7 @@ async def stream_agent_events(
         "dfs": {}
     }
     
-    config = {"configurable": {"thread_id": thread_id}}
+    config: RunnableConfig = {"configurable": {"thread_id": thread_id}}
     
     assistant_chunks: List[str] = []
     assistant_plots: List[bytes] = []
@@ -56,23 +56,26 @@ async def stream_agent_events(
             ):
                 kind = event.get("event")
                 name = event.get("name")
+                node_name = event.get("metadata", {}).get("langgraph_node", name)
                 data = event.get("data", {})
                 
                 # Standardize event for frontend
                 output_event = {
                     "type": kind,
                     "name": name,
+                    "node": node_name,
                     "data": data
                 }
                 
                 # Buffer assistant chunks (summarizer and researcher might stream)
-                if kind == "on_chat_model_stream" and name in ["summarizer", "researcher"]:
+                if kind == "on_chat_model_stream" and node_name in ["summarizer", "researcher", "clarification"]:
                     chunk = data.get("chunk", "")
                     # Use utility to safely extract text content from the chunk
                     chunk_data = convert_to_json_compatible(chunk)
                     if isinstance(chunk_data, dict) and "content" in chunk_data:
                         assistant_chunks.append(str(chunk_data["content"]))
                     else:
+                        # TODO: need better way to handle this
                         assistant_chunks.append(str(chunk_data))
                 
                 # Buffer and encode plots
@@ -80,7 +83,7 @@ async def stream_agent_events(
                     output = data.get("output", {})
                     if isinstance(output, dict) and "plots" in output:
                         plots = output["plots"]
-                        encoded_plots = []
+                        encoded_plots: list[str] = []
                         for fig in plots:
                             buf = io.BytesIO()
                             fig.savefig(buf, format="png")
@@ -131,7 +134,7 @@ async def stream_agent_events(
     except Exception as e:
         error_msg = f"Agent execution failed: {str(e)}"
         history_manager.add_message(thread_id, "assistant", error_msg)
-        yield f"data: {json.dumps({'type': 'error', 'message': error_msg})}\n\n"
+        yield f"data: {json.dumps({'type': 'error', 'data': {'message': error_msg}})}\n\n"
 
 @router.post("/stream")
 async def chat_stream(