fix(collab): continuous document text synchronization preserving local cursor

frontend/src/features/workspace/DocumentEditor.tsx

@@ -197,6 +197,7 @@ export const DocumentEditor: React.FC<DocumentEditorProps> = ({
   currentTitleRef.current = title;
   const currentBlocksRef = useRef<DocumentBlock[]>(blocks);
   currentBlocksRef.current = blocks;
+  const lastKnownUpdatedAtRef = useRef<string | null>(initialDoc?.updatedAt || null);
 
   useEffect(() => {
     if (!loading && (autoFocusTitle || (doc?.title === 'Neue Notiz' && (!doc?.blocks || doc?.blocks.length <= 1)))) {
@@ -434,6 +435,7 @@ export const DocumentEditor: React.FC<DocumentEditorProps> = ({
         });
         isSavingRef.current = false;
         lastSavedSnapshotRef.current = snapshot;
+        lastKnownUpdatedAtRef.current = updated.updatedAt || null;
         setSaveStatus('saved');
         setSaveErrorMessage(null);
         onSaveStatusChange?.('saved');
@@ -646,6 +648,9 @@ export const DocumentEditor: React.FC<DocumentEditorProps> = ({
       });
       lastSavedSnapshotRef.current = newSnapshot;
       currentSnapshotRef.current = newSnapshot;
+      if (remoteDoc.updatedAt) {
+        lastKnownUpdatedAtRef.current = remoteDoc.updatedAt;
+      }
 
       if (docRef.current) {
         docRef.current = { ...docRef.current, ...remoteDoc };
@@ -715,32 +720,61 @@ export const DocumentEditor: React.FC<DocumentEditorProps> = ({
     [docId]
   );
 
-  // Periodic poll for locks & updates (guarantees synchronization even across flaky networks)
+  // Sync when initialDoc prop changes externally
+  useEffect(() => {
+    if (initialDoc && initialDoc.id === docId && initialDoc.updatedAt && initialDoc.updatedAt !== lastKnownUpdatedAtRef.current) {
+      lastKnownUpdatedAtRef.current = initialDoc.updatedAt;
+      handleRemoteDocUpdated(initialDoc);
+    }
+  }, [initialDoc, docId, handleRemoteDocUpdated]);
+
+  // Periodic poll for locks & document text (guarantees text synchronization even without WebSockets)
   useEffect(() => {
     if (!docId) return;
-    const syncLocks = () => {
-      api.getDocLocks(docId)
-        .then((res) => {
-          if (Array.isArray(res.blockLocks)) {
+    let isCancelled = false;
+
+    const syncLocksAndDoc = async () => {
+      try {
+        // 1. Sync locks
+        const locksRes = await api.getDocLocks(docId);
+        if (isCancelled) return;
+        if (Array.isArray(locksRes.blockLocks)) {
           const map: Record<string, BlockLockInfo> = {};
-            for (const l of res.blockLocks) {
+          for (const l of locksRes.blockLocks) {
             map[l.blockId] = l;
           }
           setActiveBlockLocks(map);
         }
-          if (res.liveSession) {
-            setLiveSession(res.liveSession);
+        if (locksRes.liveSession) {
+          setLiveSession(locksRes.liveSession);
         } else {
           setLiveSession(null);
         }
-        })
-        .catch(() => {});
+
+        // 2. Sync document content if not currently actively saving
+        if (!isSavingRef.current) {
+          const remoteDoc = await api.getDocument(docId);
+          if (isCancelled || !remoteDoc) return;
+
+          // Check if server has newer or different state
+          if (remoteDoc.updatedAt && remoteDoc.updatedAt !== lastKnownUpdatedAtRef.current) {
+            console.log(`[DocumentEditor] Polling: Neuer Text-Stand vom Server (${remoteDoc.updatedAt}). Aktualisiere nicht-fokussierte Blöcke...`);
+            lastKnownUpdatedAtRef.current = remoteDoc.updatedAt;
+            handleRemoteDocUpdated(remoteDoc);
+          }
+        }
+      } catch (err) {
+        // ignore poll errors
+      }
     };
 
-    syncLocks();
-    const interval = window.setInterval(syncLocks, 3000);
-    return () => window.clearInterval(interval);
-  }, [docId]);
+    syncLocksAndDoc();
+    const interval = window.setInterval(syncLocksAndDoc, 2000);
+    return () => {
+      isCancelled = true;
+      window.clearInterval(interval);
+    };
+  }, [docId, handleRemoteDocUpdated]);
 
   // Subscribe to realtime lock & live session events
   useEffect(() => {
@@ -842,7 +876,7 @@ export const DocumentEditor: React.FC<DocumentEditorProps> = ({
         focusedBlockIdRef.current = null;
       }
       api.unlockBlock(docId, blockId).catch(() => {});
-      executeAutoSave();
+      executeAutoSave(true);
     },
     [docId, executeAutoSave]
   );