fix(frontend): loadFromState race condition + plugin stale closure (Issues #7, #8)

frontend/src/App.tsx

@@ -131,9 +131,9 @@ const CADEditor: React.FC<CADEditorProps> = ({ projectId, token, onNavigateBack
       addElement: (el) => setElements((prev) => [...prev, el]),
       removeElement: (id) => setElements((prev) => prev.filter((e) => e.id !== id)),
       updateElement: (id, props) => setElements((prev) => prev.map((e) => (e.id === id ? { ...e, ...props } : e))),
-      getElements: () => elements,
-      getLayers: () => layers,
-      getActiveLayerId: () => activeLayerId,
+      getElements: () => elementsRef.current,
+      getLayers: () => layersRef.current,
+      getActiveLayerId: () => activeLayerIdRef.current,
       showToast: (msg) => setCommandHistory((prev) => [...prev, { prefix: '·', text: msg, type: 'info' }]),
       log: (msg) => console.log(`[Plugin] ${msg}`),
     };
@@ -177,6 +177,21 @@ const CADEditor: React.FC<CADEditorProps> = ({ projectId, token, onNavigateBack
   const groupManagerRef = React.useRef(new GroupManager());
   const [groups, setGroups] = useState<ElementGroup[]>([]);
 
+  // Issue #8: Refs for PluginContext to avoid stale closures.
+  // These refs are updated on every render so PluginContext getters always return current state.
+  const elementsRef = useRef(elements);
+  elementsRef.current = elements;
+  const layersRef = useRef(layers);
+  layersRef.current = layers;
+  const blocksRef = useRef(blocks);
+  blocksRef.current = blocks;
+  const groupsRef = useRef(groups);
+  groupsRef.current = groups;
+  const bgConfigRef = useRef(bgConfig);
+  bgConfigRef.current = bgConfig;
+  const activeLayerIdRef = useRef(activeLayerId);
+  activeLayerIdRef.current = activeLayerId;
+
   // Clipboard (for copy/paste)
   const clipboardRef = React.useRef<CADElement[] | null>(null);
 
@@ -265,8 +280,11 @@ const CADEditor: React.FC<CADEditorProps> = ({ projectId, token, onNavigateBack
         setSavedStatus('gespeichert');
         setDataLoaded(true);
         // Push initial data to Yjs CRDT after load
-        if (collab.status === 'connected') {
-          const bgConfigs = bgConfig ? [bgConfig] : [];
+        // Issue #7: Only push to CRDT if backend data actually has content.
+        // Pushing empty arrays would wipe existing CRDT data from other connected clients.
+        const bgConfigs = bgConfig ? [bgConfig] : [];
+        const hasContent = data.elements.length > 0 || data.layers.length > 0 || data.blocks.length > 0 || groups.length > 0 || bgConfigs.length > 0;
+        if (collab.status === 'connected' && hasContent) {
           collab.loadFromState({
             elements: data.elements,
             layers: data.layers,