Fix UnboundLocalError in health(), switch from on_event to lifespan

vllm_middleware.py

@@ -31,19 +31,19 @@ LISTEN_PORT = int(os.environ.get("MIDDLEWARE_PORT", "8002"))
 # Extend this set as more incompatibilities are discovered.
 STRIP_PARAMS = {"logprobs", "top_logprobs"}
 
-app = FastAPI()
 client: httpx.AsyncClient | None = None
 _sglang_ready = False
 
 
-@app.on_event("startup")
-async def startup():
+async def _lifespan(app_instance):
     global client
     client = httpx.AsyncClient(
         timeout=httpx.Timeout(300.0, connect=10.0),
     )
     # Background task: wait for SGLang to become available
     asyncio.create_task(_wait_for_sglang())
+    yield
+    await client.aclose()
 
 
 async def _wait_for_sglang():
@@ -64,14 +64,13 @@ async def _wait_for_sglang():
         await asyncio.sleep(2)
 
 
-@app.on_event("shutdown")
-async def shutdown():
-    await client.aclose()
+app = FastAPI(lifespan=_lifespan)
 
 
 @app.get("/health")
 async def health():
     """Health check — haproxy polls this. Returns 200 only if SGLang is up."""
+    global _sglang_ready
     if not _sglang_ready:
         return Response(content="SGLang not ready", status_code=503)
     try: