fix: handle CORS preflight OPTIONS requests before routing

backend/main.py

@@ -130,16 +130,7 @@ class SubnetAwareCORSMiddleware(BaseHTTPMiddleware):
     async def dispatch(self, request: Request, call_next) -> Response:
         origin = request.headers.get("origin")
 
-        # Check if origin is allowed
-        if origin and is_origin_allowed(origin):
-            response = await call_next(request)
-            response.headers["Access-Control-Allow-Origin"] = origin
-            response.headers["Access-Control-Allow-Credentials"] = "true"
-            response.headers["Access-Control-Allow-Methods"] = "GET, POST, PUT, PATCH, DELETE, OPTIONS"
-            response.headers["Access-Control-Allow-Headers"] = "*"
-            return response
-
-        # Handle CORS preflight requests
+        # Handle CORS preflight (OPTIONS) requests FIRST
         if request.method == "OPTIONS":
             if origin and is_origin_allowed(origin):
                 return Response(
@@ -149,11 +140,22 @@ class SubnetAwareCORSMiddleware(BaseHTTPMiddleware):
                         "Access-Control-Allow-Credentials": "true",
                         "Access-Control-Allow-Methods": "GET, POST, PUT, PATCH, DELETE, OPTIONS",
                         "Access-Control-Allow-Headers": "*",
+                        "Content-Length": "0",
                     }
                 )
             return Response(status_code=403)
 
-        return await call_next(request)
+        # Process the actual request
+        response = await call_next(request)
+
+        # Add CORS headers to response if origin is allowed
+        if origin and is_origin_allowed(origin):
+            response.headers["Access-Control-Allow-Origin"] = origin
+            response.headers["Access-Control-Allow-Credentials"] = "true"
+            response.headers["Access-Control-Allow-Methods"] = "GET, POST, PUT, PATCH, DELETE, OPTIONS"
+            response.headers["Access-Control-Allow-Headers"] = "*"
+
+        return response
 
 app.add_middleware(SubnetAwareCORSMiddleware)
 log.info("🔒 [CORS] Subnet-aware middleware enabled (exact origins + subnet matching)")