refactor starlette as API, langgraph from openrouter

controllers.py

@@ -0,0 +1,46 @@
+import asyncio
+import uuid
+from starlette.responses import JSONResponse
+from sse_starlette.sse import EventSourceResponse
+from pydantic import BaseModel
+from langchain_core.messages import HumanMessage, AIMessage
+from chatgraph import app_graph
+from collections import defaultdict
+
+pending = defaultdict(asyncio.Queue)
+
+class ChatIn(BaseModel):
+    message: str
+
+async def create_chat(request):
+    """POST /chats  ->  returns {id: <new_chat_id>}"""
+    chat_id = str(uuid.uuid4())[:8]
+    return JSONResponse({"id": chat_id})
+
+async def post_message(request):
+    """POST /chats/{chat_id}/messages"""
+    chat_id = request.path_params["chat_id"]
+    body = await request.json()
+    msg = ChatIn(**body).message
+    await pending[chat_id].put(msg)
+    return JSONResponse({"status": "queued"})
+
+async def stream_response(request):
+    """GET /chats/{chat_id}/stream  (SSE)"""
+    chat_id = request.path_params["chat_id"]
+
+    user_msg = await pending[chat_id].get()
+
+    config = {"configurable": {"thread_id": chat_id}}
+    input_messages = [HumanMessage(content=user_msg)]
+
+    async def event_generator():
+        async for chunk, _ in app_graph.astream(
+            {"messages": input_messages},
+            config,
+            stream_mode="messages",
+        ):
+            if isinstance(chunk, AIMessage):
+                yield dict(data=chunk.content)
+
+    return EventSourceResponse(event_generator())