fix traces and surface selection when using the flip operation

src/kiri-mode/cam/client.js

@@ -747,6 +747,7 @@ CAM.init = function(kiri, api) {
         }
         // clear traces cache
         CAM.traces_clear();
+        kiri.client.clear();
         flipping = false;
         process.ops = op2;
         process.op2 = ops;

src/kiri-mode/cam/driver.js

@@ -139,6 +139,7 @@ kiri.load(api => {
         kiri.worker.cam_traces_clear = function(data, send) {
             for (let widget of Object.values(kiri.worker.cache)) {
                 delete widget.traces;
+                delete widget.topo;
             }
             send.done({});
         };