Function ws_origin_guard 

pub(super) async fn ws_origin_guard(req: Request<Body>, next: Next) -> Response

Refuse a WebSocket upgrade whose Origin is neither loopback nor allowed by --allowed-origin (is_allowed_origin).

CORS does not apply to WebSocket upgrades, so without this any web page holding the auth key could open /ws (cross-site WebSocket hijacking). The key is not sent automatically the way a cookie would be, so this is defense in depth rather than a fix for a reachable attack. Browsers always send Origin on an upgrade; srv’s native clients (launcher, agentmux-mcp) send none, so a missing header is allowed.