diff --git a/backend/src/database/SqliteAdapter.ts b/backend/src/database/SqliteAdapter.ts
index 834d0ff..2629b49 100644
--- a/backend/src/database/SqliteAdapter.ts
+++ b/backend/src/database/SqliteAdapter.ts
@@ -267,7 +267,10 @@ export class SqliteAdapter implements DatabaseInterface {
   }
 
   deleteExpiredSessions(): void {
-    this.db.prepare('DELETE FROM sessions WHERE expires_at < ?').run(Date.now());
+    // Use consistent epoch-millisecond integer comparison.
+    // <= ensures sessions expiring at exactly the current time are also deleted.
+    const now = Math.floor(Date.now());
+    this.db.prepare('DELETE FROM sessions WHERE expires_at <= ?').run(now);
   }
 
   // ─── Notifications ──────────────────────────────────
diff --git a/frontend/src/App.tsx b/frontend/src/App.tsx
index 9838d06..7ab068f 100644
--- a/frontend/src/App.tsx
+++ b/frontend/src/App.tsx
@@ -62,9 +62,6 @@ const initialKISuggestions: KISuggestion[] = [
   { id: 'sug-3', label: 'Flächen berechnen' },
 ];
 
-// Prevent duplicate drawing creation across StrictMode double-render
-const loadedProjects = new Set<string>();
-
 // ─── CAD Editor Component ───────────────────────────────
 interface CADEditorProps {
   projectId: string;
@@ -163,15 +160,18 @@ const CADEditor: React.FC<CADEditorProps> = ({ projectId, token, onNavigateBack
   // History panel
   const [historyPanelOpen, setHistoryPanelOpen] = useState(false);
 
+  // Export format selector (cross-browser replacement for nwsave)
+  const [exportFormatOpen, setExportFormatOpen] = useState(false);
+
   // Elements + undo/redo (HistoryManager)
   const [elements, setElements] = useState<CADElement[]>([]);
   const historyManagerRef = React.useRef<HistoryManager>(new HistoryManager());
   const [historyEntries, setHistoryEntries] = useState<HistoryEntry[]>([]);
   const [toolState, setToolState] = useState<ToolState | null>(null);
 
+  const seatingServiceRef = useRef<SeatingService>(new SeatingService());
   const seatCount = useMemo(() => {
-    const svc = new SeatingService();
-    return svc.countSeats(elements).total;
+    return seatingServiceRef.current.countSeats(elements).total;
   }, [elements]);
 
   // Groups
@@ -479,7 +479,7 @@ const CADEditor: React.FC<CADEditorProps> = ({ projectId, token, onNavigateBack
         setSavedStatus('Fehler beim Speichern');
       });
     }
-  }, [elements, layers, blocks, groups, bgConfig, syncHistory, token, collab]);
+  }, [layers, blocks, groups, bgConfig, syncHistory, token, collab]);
 
   const handleElementsModified = useCallback((modified: CADElement[]) => {
     setElements((prev) => {
@@ -582,11 +582,30 @@ const CADEditor: React.FC<CADEditorProps> = ({ projectId, token, onNavigateBack
     const svc = new BlockService();
     const block = svc.importSVG(svg, name, category);
     setBlocks((prev) => [...prev, block]);
+    // Push to Yjs CRDT for real-time sync
+    collab.setBlock(block);
+    // Persist to backend
+    if (drawingId && token) {
+      setSavedStatus('Speichert…');
+      createBlockTyped(token, drawingId, block)
+        .then(() => setSavedStatus('gespeichert'))
+        .catch((err) => {
+          console.error('Failed to save imported SVG block:', err);
+          setSavedStatus('Fehler beim Speichern');
+        });
+    }
     setCommandHistory((prev) => [...prev, { prefix: '·', text: `SVG importiert: ${name}`, type: 'info' }]);
-  }, []);
+  }, [collab, drawingId, token]);
 
   const handleSaveGroupAsBlock = useCallback((name: string) => {
-    const selectedEls = selectedElement ? [selectedElement] : [];
+    const selectedIds = selectedElementIdsRef.current;
+    const selectedEls = selectedIds.length > 0
+      ? elementsRef.current.filter(e => selectedIds.includes(e.id))
+      : (selectedElement ? [selectedElement] : []);
+    if (selectedEls.length === 0) {
+      setCommandHistory((prev) => [...prev, { prefix: '·', text: 'Keine Elemente ausgewählt', type: 'info' }]);
+      return;
+    }
     setBlocks((prev) => {
       const newId = `blk_grp_${Date.now()}`;
       const block: BlockDefinition = {
@@ -596,10 +615,18 @@ const CADEditor: React.FC<CADEditorProps> = ({ projectId, token, onNavigateBack
         category: 'Custom',
         elements: selectedEls.map(el => ({ ...el, id: `el_${Date.now()}_${Math.random().toString(36).slice(2, 7)}` })),
       };
+      // Push to Yjs CRDT for real-time sync
+      collab.setBlock(block);
+      // Persist to backend
+      if (drawingId && token) {
+        createBlockTyped(token, drawingId, block).catch((err) => {
+          console.error('Failed to save group block:', err);
+        });
+      }
       return [...prev, block];
     });
     setCommandHistory((prev) => [...prev, { prefix: '·', text: `Block erstellt: ${name} (${selectedEls.length} Elemente)`, type: 'info' }]);
-  }, [selectedElement]);
+  }, [selectedElement, collab, drawingId, token]);
 
   const handleBlockCategoryChange = useCallback((cat: string) => {
     setBlockCategory(cat);
@@ -763,20 +790,7 @@ const CADEditor: React.FC<CADEditorProps> = ({ projectId, token, onNavigateBack
       return;
     }
     if (action === 'export') {
-      const input = document.createElement('input');
-      input.type = 'file';
-      input.setAttribute('nwsave', '');
-      input.accept = '.dxf,.svg,.pdf,.png,.json';
-      input.onchange = () => {
-        const name = input.value || 'cad-export';
-        const ext = name.split('.').pop()?.toLowerCase() as ExportFormat;
-        if (ext && ['dxf', 'svg', 'pdf', 'png', 'json'].includes(ext)) {
-          handleExport(ext);
-        } else {
-          handleExport('dxf');
-        }
-      };
-      input.click();
+      setExportFormatOpen(true);
       return;
     }
 
@@ -1425,6 +1439,28 @@ const CADEditor: React.FC<CADEditorProps> = ({ projectId, token, onNavigateBack
           onClose={() => setHistoryPanelOpen(false)}
         />
       )}
+      {exportFormatOpen && (
+        <div className="export-format-overlay" onClick={() => setExportFormatOpen(false)}>
+          <div className="export-format-modal" onClick={(e) => e.stopPropagation()}>
+            <h3>Export als…</h3>
+            <div className="export-format-buttons">
+              {(['dxf', 'svg', 'pdf', 'png', 'json'] as ExportFormat[]).map(fmt => (
+                <button
+                  key={fmt}
+                  className="export-format-btn"
+                  onClick={() => {
+                    setExportFormatOpen(false);
+                    handleExport(fmt);
+                  }}
+                >
+                  {fmt.toUpperCase()}
+                </button>
+              ))}
+            </div>
+            <button className="export-format-cancel" onClick={() => setExportFormatOpen(false)}>Abbrechen</button>
+          </div>
+        </div>
+      )}
     </div>
   );
 };
diff --git a/frontend/src/services/api.ts b/frontend/src/services/api.ts
index eb6f825..3bc50e5 100644
--- a/frontend/src/services/api.ts
+++ b/frontend/src/services/api.ts
@@ -349,12 +349,20 @@ export async function createBlockTyped(token: string, drawingId: string, block:
   return dbBlockToFrontend(raw);
 }
 
-const projectLoadCache = new Map<string, Promise<ProjectData>>();
+const projectLoadCache = new Map<string, { promise: Promise<ProjectData>; requestId: number }>();
+const projectLoadRequestCounter = new Map<string, number>();
 
 export async function loadProjectDataTyped(token: string, projectId: string): Promise<ProjectData> {
-  // Dedup concurrent calls (React StrictMode double-render)
+  // Generate a new request ID to track the latest request for this project
+  const currentRequestId = (projectLoadRequestCounter.get(projectId) ?? 0) + 1;
+  projectLoadRequestCounter.set(projectId, currentRequestId);
+
+  // Dedup concurrent calls (React StrictMode double-render): if there is an in-flight
+  // request with the same ID, reuse it. Otherwise start a fresh one.
   const existing = projectLoadCache.get(projectId);
-  if (existing) return existing;
+  if (existing && existing.requestId === currentRequestId - 1) {
+    return existing.promise;
+  }
 
   const promise = (async () => {
     const drawings = await getDrawings(token, projectId);
@@ -373,6 +381,13 @@ export async function loadProjectDataTyped(token: string, projectId: string): Pr
       getBlocks(token, drawing.id),
     ]);
 
+    // Only use the result if this is still the latest request for this project
+    const latestRequestId = projectLoadRequestCounter.get(projectId);
+    if (latestRequestId !== currentRequestId) {
+      // A newer request superseded this one — reject to prevent stale data
+      throw new Error('Superseded by a newer load request');
+    }
+
     return {
       project,
       drawing,
@@ -382,8 +397,14 @@ export async function loadProjectDataTyped(token: string, projectId: string): Pr
     };
   })();
 
-  projectLoadCache.set(projectId, promise);
-  promise.finally(() => projectLoadCache.delete(projectId));
+  projectLoadCache.set(projectId, { promise, requestId: currentRequestId });
+  promise.finally(() => {
+    // Only clear cache if this is still the latest request
+    const cached = projectLoadCache.get(projectId);
+    if (cached && cached.requestId === currentRequestId) {
+      projectLoadCache.delete(projectId);
+    }
+  });
   return promise;
 }
 
diff --git a/frontend/src/styles.css b/frontend/src/styles.css
index 6b44431..47c2ae2 100644
--- a/frontend/src/styles.css
+++ b/frontend/src/styles.css
@@ -2212,3 +2212,61 @@ body.drawer-open { overflow: hidden; }
 .tree-drag-after { border-bottom: 2px solid var(--color-primary); }
 .tree-drag-inside { background: var(--color-surface-2); outline: 2px solid var(--color-primary); outline-offset: -2px; }
 .tree-dragging { opacity: 0.5; }
+
+/* Export format selector overlay */
+.export-format-overlay {
+  position: fixed;
+  top: 0; left: 0; right: 0; bottom: 0;
+  background: rgba(0,0,0,0.5);
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  z-index: 9999;
+}
+.export-format-modal {
+  background: var(--color-surface-1, #1e1e2e);
+  border: 1px solid var(--color-border, #333);
+  border-radius: 8px;
+  padding: 20px;
+  min-width: 300px;
+  box-shadow: 0 4px 20px rgba(0,0,0,0.4);
+}
+.export-format-modal h3 {
+  margin: 0 0 16px 0;
+  font-size: 16px;
+  color: var(--color-text, #e0e0e0);
+}
+.export-format-buttons {
+  display: flex;
+  flex-wrap: wrap;
+  gap: 8px;
+  margin-bottom: 16px;
+}
+.export-format-btn {
+  padding: 10px 20px;
+  border: 1px solid var(--color-border, #444);
+  border-radius: 4px;
+  background: var(--color-surface-2, #2a2a3e);
+  color: var(--color-text, #e0e0e0);
+  cursor: pointer;
+  font-size: 14px;
+  font-weight: 600;
+  transition: background 0.2s;
+}
+.export-format-btn:hover {
+  background: var(--color-primary, #3498db);
+  color: white;
+}
+.export-format-cancel {
+  width: 100%;
+  padding: 8px;
+  border: 1px solid var(--color-border, #444);
+  border-radius: 4px;
+  background: transparent;
+  color: var(--color-text, #e0e0e0);
+  cursor: pointer;
+  font-size: 13px;
+}
+.export-format-cancel:hover {
+  background: var(--color-surface-2, #2a2a3e);
+}