fix(sync): eliminate zombie focus, flush debounced state on window blur, remove stale closures and buffer ws messages

frontend/src/features/workspace/DocumentEditor.tsx

@@ -196,10 +196,12 @@ export const DocumentEditor: React.FC<DocumentEditorProps> = ({
       switch (evt.type) {
         case 'doc_state': {
           if (evt.title !== undefined) {
-            const isTitleFocused =
+            const isTitleActivelyEditing =
               titleInputRef.current !== null &&
-              document.activeElement === titleInputRef.current;
-            if (!isTitleFocused) {
+              document.activeElement === titleInputRef.current &&
+              typeof document !== 'undefined' &&
+              document.hasFocus();
+            if (!isTitleActivelyEditing) {
               setTitle(evt.title);
             }
           }
@@ -211,10 +213,12 @@ export const DocumentEditor: React.FC<DocumentEditorProps> = ({
 
         case 'title_updated': {
           if (evt.title !== undefined) {
-            const isTitleFocused =
+            const isTitleActivelyEditing =
               titleInputRef.current !== null &&
-              document.activeElement === titleInputRef.current;
-            if (!isTitleFocused) {
+              document.activeElement === titleInputRef.current &&
+              typeof document !== 'undefined' &&
+              document.hasFocus();
+            if (!isTitleActivelyEditing) {
               setTitle(evt.title);
             }
             if (docRef.current) {
@@ -407,6 +411,27 @@ export const DocumentEditor: React.FC<DocumentEditorProps> = ({
     }, 250);
   };
 
+  const handleTitleBlur = () => {
+    if (titleDebounceRef.current !== null) {
+      window.clearTimeout(titleDebounceRef.current);
+      titleDebounceRef.current = null;
+      sendTitleUpdated(title);
+    }
+  };
+
+  // Flush title debouncing on window blur so background window never holds stale pending title
+  useEffect(() => {
+    const handleWindowBlur = () => {
+      if (titleDebounceRef.current !== null) {
+        window.clearTimeout(titleDebounceRef.current);
+        titleDebounceRef.current = null;
+        sendTitleUpdated(title);
+      }
+    };
+    window.addEventListener('blur', handleWindowBlur);
+    return () => window.removeEventListener('blur', handleWindowBlur);
+  }, [title, sendTitleUpdated]);
+
   const handleUpdateBlock = useCallback(
     (updatedBlock: DocumentBlock) => {
       setBlocks((prev) =>
@@ -920,6 +945,7 @@ export const DocumentEditor: React.FC<DocumentEditorProps> = ({
                 value={title}
                 readOnly={!canEdit}
                 onChange={handleTitleChange}
+                onBlur={handleTitleBlur}
                 placeholder="Titel der Notiz…"
                 className="flex-1 min-w-0 text-xl sm:text-2xl font-bold text-main bg-transparent border-0 focus:outline-none focus:ring-0 tracking-tight"
               />