fix: close hijacks racing with shutdown

proxy/proxy.go

@@ -33,6 +33,8 @@ type Handler struct {
 	connMu       sync.Mutex
 	conns        map[net.Conn]struct{}
 	connChanged  chan struct{}
+	closing      bool
+	closed       bool
 }
 
 // Options 控制反代连接上游时的网络行为。
@@ -253,7 +255,9 @@ func (h *Handler) serveRequestBodyError(cw *captureWriter, r *http.Request, st *
 func (h *Handler) Shutdown(ctx context.Context) error {
 	for {
 		h.connMu.Lock()
+		h.closing = true
 		if len(h.conns) == 0 {
+			h.closed = true
 			h.connMu.Unlock()
 			return nil
 		}
@@ -284,6 +288,11 @@ func (h *Handler) trackConn(conn net.Conn) net.Conn {
 		h.connMu.Unlock()
 	}
 	h.connMu.Lock()
+	if h.closing || h.closed {
+		h.connMu.Unlock()
+		_ = conn.Close()
+		return conn
+	}
 	h.conns[tracked] = struct{}{}
 	close(h.connChanged)
 	h.connChanged = make(chan struct{})