Implement local-first canvas sync and fix drag edge stability

components/canvas/canvas-delete-handlers.ts

@@ -16,6 +16,7 @@ import { getNodeDeleteBlockReason, isOptimisticEdgeId } from "./canvas-helpers";
 
 type UseCanvasDeleteHandlersParams = {
   canvasId: Id<"canvases">;
+  isOffline: boolean;
   nodes: RFNode[];
   edges: RFEdge[];
   deletingNodeIds: MutableRefObject<Set<string>>;
@@ -33,6 +34,7 @@ type UseCanvasDeleteHandlersParams = {
 
 export function useCanvasDeleteHandlers({
   canvasId,
+  isOffline,
   nodes,
   edges,
   deletingNodeIds,
@@ -53,6 +55,14 @@ export function useCanvasDeleteHandlers({
       nodes: RFNode[];
       edges: RFEdge[];
     }) => {
+      if (isOffline && (matchingNodes.length > 0 || matchingEdges.length > 0)) {
+        toast.warning(
+          "Offline aktuell nicht unterstützt",
+          "Löschen ist in Stufe 1 nur online verfügbar.",
+        );
+        return false;
+      }
+
       if (matchingNodes.length === 0) {
         return true;
       }
@@ -90,7 +100,7 @@ export function useCanvasDeleteHandlers({
 
       return true;
     },
-    [],
+    [isOffline],
   );
 
   const onNodesDelete = useCallback(