fix: history/undo/redo — re-init after project load + sync to Yjs CRDT

frontend/src/App.tsx

@@ -238,18 +238,30 @@ const CADEditor: React.FC<CADEditorProps> = ({ projectId, token, onNavigateBack
     if (snap) {
       restoreSnapshot(snap);
       syncHistory();
+      // Sync restored state to Yjs CRDT to prevent collab overwrite
+      if (collab.status === 'connected') {
+        for (const el of snap.elements) collab.setElement(el);
+        for (const layer of snap.layers) collab.setLayer(layer);
+        for (const block of snap.blocks) collab.setBlock(block);
+      }
       setCommandHistory((prev) => [...prev, { prefix: '·', text: 'Rückgängig: letzte Aktion', type: 'info' }]);
     }
-  }, [restoreSnapshot, syncHistory]);
+  }, [restoreSnapshot, syncHistory, collab]);
 
   const handleRedo = useCallback(() => {
     const snap = historyManagerRef.current.redo();
     if (snap) {
       restoreSnapshot(snap);
       syncHistory();
+      // Sync restored state to Yjs CRDT to prevent collab overwrite
+      if (collab.status === 'connected') {
+        for (const el of snap.elements) collab.setElement(el);
+        for (const layer of snap.layers) collab.setLayer(layer);
+        for (const block of snap.blocks) collab.setBlock(block);
+      }
       setCommandHistory((prev) => [...prev, { prefix: '·', text: 'Wiederherstellen: letzte Aktion', type: 'info' }]);
     }
-  }, [restoreSnapshot, syncHistory]);
+  }, [restoreSnapshot, syncHistory, collab]);
 
   const pushHistorySnapshot = useCallback((label: string) => {
     historyManagerRef.current.pushSnapshot({
@@ -318,6 +330,15 @@ const CADEditor: React.FC<CADEditorProps> = ({ projectId, token, onNavigateBack
         }
         setSavedStatus('gespeichert');
         setDataLoaded(true);
+        // Re-initialize HistoryManager with loaded project state so undo does not jump back to empty initial state
+        historyManagerRef.current.initialize({
+          elements: data.elements,
+          layers: data.layers.length > 0 ? data.layers : initialLayers,
+          blocks: data.blocks,
+          groups: [],
+          bgConfig: null,
+        });
+        syncHistory();
         // Push initial data to Yjs CRDT after load
         // Issue #7: Only push to CRDT if backend data actually has content.
         // Pushing empty arrays would wipe existing CRDT data from other connected clients.