fix(courses): address 2nd review — folder-view layout, drop highlight, validation parity, a11y, i18n

Per review (wyuc, CHANGES_REQUESTED on 9f77686f):

P1 — folder view layout: opening a folder compacts the hero and surfaces
the library content; the centered header shows a single path
"Recent > Folder name"; the empty-folder state sits directly below it;
clicking Recent returns to the root grid. The duplicate content
breadcrumb is dropped (kept only for search).

P2 — correctness & a11y:
- Clear the folder drop highlight on every drag exit (dragenter counter)
  and gate it on the text/stage-id payload.
- Duplicate-name check in the dialog is now case-insensitive, matching
  the storage boundary; FolderNameError is mapped to specific messages.
- Renames report the actual submitted width, not a hardcoded 0.
- createFolder/renameFolder run read-check-write in one read-write
  transaction so the uniqueness invariant cannot race across tabs.
- The move-menu trigger is focus-visible and pointer-coarse reachable
  (visible on touch / keyboard), not hover-only.

Extra:
- Empty library (no courses, no folders) shows a dedicated hint instead
  of the search-empty string.
- Translate all newly added folder strings across ja/ko/pt/ru/ar, fix
  Simplified-Chinese text in zh-TW, and add the emptyLibraryHint key.

app/page.tsx

@@ -66,6 +66,7 @@ import {
   type DeleteFolderMode,
 } from '@/lib/utils/stage-storage';
 import type { FolderRecord } from '@/lib/utils/database';
+import { displayNameWidth, FOLDER_NAME_MAX_WIDTH } from '@/lib/utils/folder-name-validation';
 import { FolderCard } from '@/components/discovery/folder-card';
 import { NewFolderDialog, DeleteFolderDialog } from '@/components/discovery/folder-dialogs';
 import { MoveToFolderMenu } from '@/components/discovery/move-to-folder-menu';
@@ -330,7 +331,11 @@ function HomePage() {
       } catch (err) {
         if (err instanceof FolderNameError) {
           if (err.kind === 'duplicate') return t('classroom.folderNameExists');
-          if (err.kind === 'tooLong') return t('classroom.folderWidth', { width: 0, max: 40 });
+          if (err.kind === 'tooLong')
+            return t('classroom.folderWidth', {
+              width: displayNameWidth(trimmed),
+              max: FOLDER_NAME_MAX_WIDTH,
+            });
           return t('classroom.folderNameHint');
         }
         log.error('Failed to rename folder:', err);
@@ -730,7 +735,9 @@ function HomePage() {
         transition={{ duration: 0.6, ease: 'easeOut' }}
         className={cn(
           'relative z-20 w-full max-w-[800px] flex flex-col items-center',
-          classrooms.length === 0 ? 'justify-center min-h-[calc(100dvh-8rem)]' : 'mt-[10vh]',
+          classrooms.length === 0 && !effectiveCurrentFolderId
+            ? 'justify-center min-h-[calc(100dvh-8rem)]'
+            : 'mt-[10vh]',
         )}
       >
         {/* ── Logo ── */}
@@ -957,6 +964,14 @@ function HomePage() {
               >
                 <Clock className="size-3.5" />
                 {t('classroom.recentClassrooms')}
+                {currentFolder && (
+                  <>
+                    <ChevronRight className="size-3 opacity-40" />
+                    <span className="text-foreground/80 truncate max-w-[160px]">
+                      {currentFolder.name}
+                    </span>
+                  </>
+                )}
                 <span className="text-[11px] tabular-nums opacity-60">{classrooms.length}</span>
                 <motion.div
                   animate={{ rotate: recentOpen ? 180 : 0 }}
@@ -1101,22 +1116,16 @@ function HomePage() {
               >
                 {effectiveFolders.length === 0 && classrooms.length === 0 ? (
                   <div className="pt-8 pb-2 text-center text-[13px] text-muted-foreground/60">
-                    {t('classroom.searchEmpty')}
+                    {t('classroom.emptyLibraryHint')}
                   </div>
                 ) : !isSearching &&
                   effectiveCurrentFolderId &&
                   currentFolderClassrooms.length === 0 ? (
-                  // Empty folder: hint + back link.
+                  // Empty folder: hint directly below the centered path bar.
                   <div className="pt-8 text-center">
                     <p className="text-[14px] text-muted-foreground">
                       {t('classroom.emptyFolderHint')}
                     </p>
-                    <button
-                      onClick={() => setCurrentFolderId(undefined)}
-                      className="mt-3 text-[13px] text-violet-500 hover:text-violet-600"
-                    >
-                      {t('classroom.backToAllCourses')}
-                    </button>
                   </div>
                 ) : isSearching && filteredClassrooms.length === 0 ? (
                   <div className="pt-8 pb-2 text-center text-[13px] text-muted-foreground/60">
@@ -1124,40 +1133,28 @@ function HomePage() {
                   </div>
                 ) : (
                   <div className="pt-8">
-                    {/* Breadcrumb — shown inside a folder or while searching. */}
-                    {(effectiveCurrentFolderId || isSearching) && (
+                    {/* Breadcrumb — shown only while searching (the folder path
+                        already lives in the centered header above). */}
+                    {isSearching && (
                       <div className="mb-4 flex items-center gap-1.5 text-[13px] text-muted-foreground">
                         <button
                           type="button"
                           onClick={() => {
                             setCurrentFolderId(undefined);
-                            if (isSearching) {
-                              setSearchQuery('');
-                              setSearchOpen(false);
-                            }
+                            setSearchQuery('');
+                            setSearchOpen(false);
                           }}
                           className="hover:text-foreground transition-colors"
                         >
                           {t('classroom.recentClassrooms')}
                         </button>
                         <ChevronRight className="size-3.5" />
-                        {isSearching ? (
-                          <>
-                            <span className="text-foreground font-medium">
-                              {t('classroom.searchResults')}
-                            </span>
-                            <span className="ml-1.5 text-[12px] text-muted-foreground tabular-nums">
-                              ({filteredClassrooms.length})
-                            </span>
-                          </>
-                        ) : (
-                          <>
-                            <Folder className="size-3.5 text-violet-500" />
-                            <span className="text-foreground font-medium truncate max-w-[60vw]">
-                              {currentFolder?.name}
-                            </span>
-                          </>
-                        )}
+                        <span className="text-foreground font-medium">
+                          {t('classroom.searchResults')}
+                        </span>
+                        <span className="ml-1.5 text-[12px] text-muted-foreground tabular-nums">
+                          ({filteredClassrooms.length})
+                        </span>
                       </div>
                     )}
 

components/discovery/folder-card.tsx

@@ -46,6 +46,7 @@ export function FolderCard({
   const [error, setError] = useState<string | null>(null);
   const [submitting, setSubmitting] = useState(false);
   const [dropActive, setDropActive] = useState(false);
+  const dragDepth = useRef(0);
   const inputRef = useRef<HTMLInputElement>(null);
   const thumbRef = useRef<HTMLDivElement>(null);
   const [thumbWidth, setThumbWidth] = useState(0);
@@ -90,18 +91,28 @@ export function FolderCard({
     <div
       className="group cursor-pointer"
       onClick={editing ? undefined : onOpen}
-      onDragOver={(e) => {
+      onDragEnter={(e) => {
         if (editing) return;
-        e.preventDefault();
-        e.dataTransfer.dropEffect = 'move';
+        // Only react to course-card drags (carrying a stage-id payload).
+        if (!Array.from(e.dataTransfer.types).includes('text/stage-id')) return;
+        dragDepth.current += 1;
         setDropActive(true);
       }}
-      onDragLeave={(e) => {
-        // Only clear when leaving the card entirely, not when crossing children.
-        if (e.currentTarget === e.target) setDropActive(false);
+      onDragOver={(e) => {
+        if (editing) return;
+        if (!Array.from(e.dataTransfer.types).includes('text/stage-id')) return;
+        e.preventDefault();
+        e.dataTransfer.dropEffect = 'move';
+      }}
+      onDragLeave={() => {
+        // dragenter/dragleave fire per child element; balance them with a
+        // counter so the highlight clears only when the pointer fully exits.
+        dragDepth.current = Math.max(0, dragDepth.current - 1);
+        if (dragDepth.current === 0) setDropActive(false);
       }}
       onDrop={(e) => {
         e.preventDefault();
+        dragDepth.current = 0;
         setDropActive(false);
         const stageId = e.dataTransfer.getData('text/stage-id');
         if (stageId) onDropCourse(stageId);

components/discovery/folder-dialogs.tsx

@@ -18,6 +18,7 @@ import {
   validateFolderName,
 } from '@/lib/utils/folder-name-validation';
 import type { FolderRecord } from '@/lib/utils/database';
+import { FolderNameError } from '@/lib/utils/stage-storage';
 
 // ============ F1: New folder dialog ============
 
@@ -56,7 +57,8 @@ export function NewFolderDialog({
       return;
     }
     const trimmed = name.trim();
-    if (folders.some((f) => f.name === trimmed)) {
+    // Case-insensitive duplicate check, matching the storage-boundary rule.
+    if (folders.some((f) => f.name.toLowerCase() === trimmed.toLowerCase())) {
       setError(t('classroom.folderNameExists'));
       return;
     }
@@ -68,8 +70,22 @@ export function NewFolderDialog({
     try {
       await onCreate(trimmed);
       onOpenChange(false);
-    } catch {
-      setError(t('classroom.folderCreateFailed'));
+    } catch (err) {
+      // Map the storage-boundary error to a specific message when possible.
+      if (err instanceof FolderNameError) {
+        setError(
+          err.kind === 'duplicate'
+            ? t('classroom.folderNameExists')
+            : err.kind === 'tooLong'
+              ? t('classroom.folderWidth', {
+                  width: displayNameWidth(trimmed),
+                  max: FOLDER_NAME_MAX_WIDTH,
+                })
+              : t('classroom.folderNameHint'),
+        );
+      } else {
+        setError(t('classroom.folderCreateFailed'));
+      }
     } finally {
       setSubmitting(false);
     }

components/discovery/move-to-folder-menu.tsx

@@ -42,7 +42,7 @@ export function MoveToFolderMenu({
           title={t('classroom.moveToFolder')}
           onClick={(e) => e.stopPropagation()}
           onPointerDown={(e) => e.stopPropagation()}
-          className="absolute top-2 right-20 size-7 inline-flex items-center justify-center rounded-full bg-black/30 hover:bg-black/50 text-white hover:text-white backdrop-blur-sm opacity-0 group-hover:opacity-100 transition-opacity z-10"
+          className="absolute top-2 right-20 size-7 inline-flex items-center justify-center rounded-full bg-black/30 hover:bg-black/50 text-white hover:text-white backdrop-blur-sm opacity-0 transition-opacity z-10 focus-visible:opacity-100 focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-violet-400 pointer-coarse:opacity-100 group-hover:opacity-100"
         >
           <FolderInput className="size-3.5" />
         </button>

lib/i18n/locales/ar-SA.json

@@ -869,7 +869,7 @@
     "searchEmpty": "لا توجد دروس مطابقة",
     "newFolderTitle": "New folder",
     "newFolderDesc": "Group courses by topic or use for easier access.",
-    "newFolderInline": "New folder…",
+    "newFolderInline": "مجلد جديد",
     "folderNameLabel": "Folder name",
     "folderNamePlaceholder": "e.g. Math, English, Major courses",
     "folderNameHint": "CJK and Latin both OK; spaces count.",
@@ -877,8 +877,8 @@
     "folderCountLimit": "Folder count limit reached",
     "folderWidth": "Width {{width}}/{{max}}",
     "folderCreate": "Create",
-    "folderBadge": "Folder",
-    "folderCourseCountUnit": "courses",
+    "folderBadge": "مجلد",
+    "folderCourseCountUnit": "دورة",
     "deleteFolderTitle": "Delete folder \"{{name}}\"",
     "deleteFolderEmptyDesc": "This folder is empty. Deletion cannot be undone.",
     "deleteFolderDesc": "This folder has {{count}} course(s). Choose how to handle them.",
@@ -887,16 +887,17 @@
     "deleteFolderRemoveTitle": "Remove courses from \"My courses\" too",
     "deleteFolderRemoveDesc": "Courses leave My courses and chat history is wiped. Irreversible.",
     "deleteFolderRemoveAction": "Remove and delete",
-    "moveToFolder": "Move to folder",
-    "moveToFolderLabel": "Move to…",
-    "ungrouped": "Ungrouped",
-    "searchResults": "Search results",
-    "folderCreateFailed": "Failed to create folder",
-    "folderRenameFailed": "Failed to rename folder",
-    "folderDeleteFailed": "Failed to delete folder",
-    "moveFailed": "Failed to move course",
-    "emptyFolderHint": "This folder is empty",
-    "backToAllCourses": "Back to all courses"
+    "moveToFolder": "نقل إلى مجلد",
+    "moveToFolderLabel": "نقل إلى مجلد",
+    "ungrouped": "غير مصنّف",
+    "searchResults": "نتائج البحث",
+    "folderCreateFailed": "فشل إنشاء المجلد",
+    "folderRenameFailed": "فشلت إعادة تسمية المجلد",
+    "folderDeleteFailed": "فشل حذف المجلد",
+    "moveFailed": "فشل نقل الدورة",
+    "emptyFolderHint": "هذا المجلد فارغ",
+    "backToAllCourses": "العودة إلى كل الدورات",
+    "emptyLibraryHint": "لا توجد دورات بعد — أنشئ واحدة بالأعلى أو استورد دورة."
   },
   "upload": {
     "pdfSizeLimit": "يدعم ملفات PDF حتى 50 ميغابايت",

lib/i18n/locales/en-US.json

@@ -896,7 +896,8 @@
     "folderDeleteFailed": "Failed to delete folder",
     "moveFailed": "Failed to move course",
     "emptyFolderHint": "This folder is empty",
-    "backToAllCourses": "Back to all courses"
+    "backToAllCourses": "Back to all courses",
+    "emptyLibraryHint": "No courses yet — create one above, or import a course."
   },
   "upload": {
     "pdfSizeLimit": "Supports PDF files up to 50MB",

lib/i18n/locales/es-MX.json

@@ -896,7 +896,8 @@
     "folderDeleteFailed": "Error al eliminar la carpeta",
     "moveFailed": "Error al mover el curso",
     "emptyFolderHint": "Esta carpeta está vacía",
-    "backToAllCourses": "Volver a todos los cursos"
+    "backToAllCourses": "Volver a todos los cursos",
+    "emptyLibraryHint": "Aún no hay cursos — crea uno arriba o importa un curso."
   },
   "upload": {
     "pdfSizeLimit": "Admite archivos PDF de hasta 50 MB",

lib/i18n/locales/ja-JP.json

@@ -869,7 +869,7 @@
     "searchEmpty": "該当するコースが見つかりません",
     "newFolderTitle": "New folder",
     "newFolderDesc": "Group courses by topic or use for easier access.",
-    "newFolderInline": "New folder…",
+    "newFolderInline": "新規フォルダ",
     "folderNameLabel": "Folder name",
     "folderNamePlaceholder": "e.g. Math, English, Major courses",
     "folderNameHint": "CJK and Latin both OK; spaces count.",
@@ -877,8 +877,8 @@
     "folderCountLimit": "Folder count limit reached",
     "folderWidth": "Width {{width}}/{{max}}",
     "folderCreate": "Create",
-    "folderBadge": "Folder",
-    "folderCourseCountUnit": "courses",
+    "folderBadge": "フォルダ",
+    "folderCourseCountUnit": "件のコース",
     "deleteFolderTitle": "Delete folder \"{{name}}\"",
     "deleteFolderEmptyDesc": "This folder is empty. Deletion cannot be undone.",
     "deleteFolderDesc": "This folder has {{count}} course(s). Choose how to handle them.",
@@ -887,16 +887,17 @@
     "deleteFolderRemoveTitle": "Remove courses from \"My courses\" too",
     "deleteFolderRemoveDesc": "Courses leave My courses and chat history is wiped. Irreversible.",
     "deleteFolderRemoveAction": "Remove and delete",
-    "moveToFolder": "Move to folder",
-    "moveToFolderLabel": "Move to…",
-    "ungrouped": "Ungrouped",
-    "searchResults": "Search results",
-    "folderCreateFailed": "Failed to create folder",
-    "folderRenameFailed": "Failed to rename folder",
-    "folderDeleteFailed": "Failed to delete folder",
-    "moveFailed": "Failed to move course",
-    "emptyFolderHint": "This folder is empty",
-    "backToAllCourses": "Back to all courses"
+    "moveToFolder": "フォルダに移動",
+    "moveToFolderLabel": "フォルダに移動",
+    "ungrouped": "未分類",
+    "searchResults": "検索結果",
+    "folderCreateFailed": "フォルダの作成に失敗しました",
+    "folderRenameFailed": "フォルダの名前変更に失敗しました",
+    "folderDeleteFailed": "フォルダの削除に失敗しました",
+    "moveFailed": "コースの移動に失敗しました",
+    "emptyFolderHint": "このフォルダは空です",
+    "backToAllCourses": "すべてのコースに戻る",
+    "emptyLibraryHint": "まだコースがありません。上で作成するか、コースをインポートしてください。"
   },
   "upload": {
     "pdfSizeLimit": "50MBまでのPDFファイルに対応しています",

lib/i18n/locales/ko-KR.json

@@ -869,7 +869,7 @@
     "searchEmpty": "검색 결과에 해당하는 강좌가 없습니다",
     "newFolderTitle": "New folder",
     "newFolderDesc": "Group courses by topic or use for easier access.",
-    "newFolderInline": "New folder…",
+    "newFolderInline": "새 폴더",
     "folderNameLabel": "Folder name",
     "folderNamePlaceholder": "e.g. Math, English, Major courses",
     "folderNameHint": "CJK and Latin both OK; spaces count.",
@@ -877,8 +877,8 @@
     "folderCountLimit": "Folder count limit reached",
     "folderWidth": "Width {{width}}/{{max}}",
     "folderCreate": "Create",
-    "folderBadge": "Folder",
-    "folderCourseCountUnit": "courses",
+    "folderBadge": "폴더",
+    "folderCourseCountUnit": "개 강의",
     "deleteFolderTitle": "Delete folder \"{{name}}\"",
     "deleteFolderEmptyDesc": "This folder is empty. Deletion cannot be undone.",
     "deleteFolderDesc": "This folder has {{count}} course(s). Choose how to handle them.",
@@ -887,16 +887,17 @@
     "deleteFolderRemoveTitle": "Remove courses from \"My courses\" too",
     "deleteFolderRemoveDesc": "Courses leave My courses and chat history is wiped. Irreversible.",
     "deleteFolderRemoveAction": "Remove and delete",
-    "moveToFolder": "Move to folder",
-    "moveToFolderLabel": "Move to…",
-    "ungrouped": "Ungrouped",
-    "searchResults": "Search results",
-    "folderCreateFailed": "Failed to create folder",
-    "folderRenameFailed": "Failed to rename folder",
-    "folderDeleteFailed": "Failed to delete folder",
-    "moveFailed": "Failed to move course",
-    "emptyFolderHint": "This folder is empty",
-    "backToAllCourses": "Back to all courses"
+    "moveToFolder": "폴더로 이동",
+    "moveToFolderLabel": "폴더로 이동",
+    "ungrouped": "미분류",
+    "searchResults": "검색 결과",
+    "folderCreateFailed": "폴더 만들기에 실패했습니다",
+    "folderRenameFailed": "폴더 이름 변경에 실패했습니다",
+    "folderDeleteFailed": "폴더 삭제에 실패했습니다",
+    "moveFailed": "강의 이동에 실패했습니다",
+    "emptyFolderHint": "이 폴더가 비어 있습니다",
+    "backToAllCourses": "전체 강의로 돌아가기",
+    "emptyLibraryHint": "아직 강의가 없습니다. 위에서 만들거나 강의를 가져오세요."
   },
   "upload": {
     "pdfSizeLimit": "최대 50MB PDF 파일을 지원합니다",

lib/i18n/locales/pt-BR.json

@@ -869,7 +869,7 @@
     "searchEmpty": "Nenhum curso corresponde à sua busca",
     "newFolderTitle": "New folder",
     "newFolderDesc": "Group courses by topic or use for easier access.",
-    "newFolderInline": "New folder…",
+    "newFolderInline": "Nova pasta",
     "folderNameLabel": "Folder name",
     "folderNamePlaceholder": "e.g. Math, English, Major courses",
     "folderNameHint": "CJK and Latin both OK; spaces count.",
@@ -877,8 +877,8 @@
     "folderCountLimit": "Folder count limit reached",
     "folderWidth": "Width {{width}}/{{max}}",
     "folderCreate": "Create",
-    "folderBadge": "Folder",
-    "folderCourseCountUnit": "courses",
+    "folderBadge": "Pasta",
+    "folderCourseCountUnit": "cursos",
     "deleteFolderTitle": "Delete folder \"{{name}}\"",
     "deleteFolderEmptyDesc": "This folder is empty. Deletion cannot be undone.",
     "deleteFolderDesc": "This folder has {{count}} course(s). Choose how to handle them.",
@@ -887,16 +887,17 @@
     "deleteFolderRemoveTitle": "Remove courses from \"My courses\" too",
     "deleteFolderRemoveDesc": "Courses leave My courses and chat history is wiped. Irreversible.",
     "deleteFolderRemoveAction": "Remove and delete",
-    "moveToFolder": "Move to folder",
-    "moveToFolderLabel": "Move to…",
-    "ungrouped": "Ungrouped",
-    "searchResults": "Search results",
-    "folderCreateFailed": "Failed to create folder",
-    "folderRenameFailed": "Failed to rename folder",
-    "folderDeleteFailed": "Failed to delete folder",
-    "moveFailed": "Failed to move course",
-    "emptyFolderHint": "This folder is empty",
-    "backToAllCourses": "Back to all courses"
+    "moveToFolder": "Mover para pasta",
+    "moveToFolderLabel": "Mover para a pasta",
+    "ungrouped": "Sem pasta",
+    "searchResults": "Resultados da busca",
+    "folderCreateFailed": "Falha ao criar a pasta",
+    "folderRenameFailed": "Falha ao renomear a pasta",
+    "folderDeleteFailed": "Falha ao excluir a pasta",
+    "moveFailed": "Falha ao mover o curso",
+    "emptyFolderHint": "Esta pasta está vazia",
+    "backToAllCourses": "Voltar para todos os cursos",
+    "emptyLibraryHint": "Nenhum curso ainda — crie um acima ou importe um curso."
   },
   "upload": {
     "pdfSizeLimit": "Suporta arquivos PDF de até 50 MB",

lib/i18n/locales/ru-RU.json

@@ -869,7 +869,7 @@
     "searchEmpty": "Курсы не найдены",
     "newFolderTitle": "New folder",
     "newFolderDesc": "Group courses by topic or use for easier access.",
-    "newFolderInline": "New folder…",
+    "newFolderInline": "Новая папка",
     "folderNameLabel": "Folder name",
     "folderNamePlaceholder": "e.g. Math, English, Major courses",
     "folderNameHint": "CJK and Latin both OK; spaces count.",
@@ -877,8 +877,8 @@
     "folderCountLimit": "Folder count limit reached",
     "folderWidth": "Width {{width}}/{{max}}",
     "folderCreate": "Create",
-    "folderBadge": "Folder",
-    "folderCourseCountUnit": "courses",
+    "folderBadge": "Папка",
+    "folderCourseCountUnit": "курсов",
     "deleteFolderTitle": "Delete folder \"{{name}}\"",
     "deleteFolderEmptyDesc": "This folder is empty. Deletion cannot be undone.",
     "deleteFolderDesc": "This folder has {{count}} course(s). Choose how to handle them.",
@@ -887,16 +887,17 @@
     "deleteFolderRemoveTitle": "Remove courses from \"My courses\" too",
     "deleteFolderRemoveDesc": "Courses leave My courses and chat history is wiped. Irreversible.",
     "deleteFolderRemoveAction": "Remove and delete",
-    "moveToFolder": "Move to folder",
-    "moveToFolderLabel": "Move to…",
-    "ungrouped": "Ungrouped",
-    "searchResults": "Search results",
-    "folderCreateFailed": "Failed to create folder",
-    "folderRenameFailed": "Failed to rename folder",
-    "folderDeleteFailed": "Failed to delete folder",
-    "moveFailed": "Failed to move course",
-    "emptyFolderHint": "This folder is empty",
-    "backToAllCourses": "Back to all courses"
+    "moveToFolder": "Переместить в папку",
+    "moveToFolderLabel": "Переместить в папку",
+    "ungrouped": "Без папки",
+    "searchResults": "Результаты поиска",
+    "folderCreateFailed": "Не удалось создать папку",
+    "folderRenameFailed": "Не удалось переименовать папку",
+    "folderDeleteFailed": "Не удалось удалить папку",
+    "moveFailed": "Не удалось переместить курс",
+    "emptyFolderHint": "Эта папка пуста",
+    "backToAllCourses": "Назад ко всем курсам",
+    "emptyLibraryHint": "Курсов пока нет — создайте выше или импортируйте курс."
   },
   "upload": {
     "pdfSizeLimit": "Поддержка PDF до 50 МБ",

lib/i18n/locales/zh-CN.json

@@ -896,7 +896,8 @@
     "folderDeleteFailed": "删除文件夹失败",
     "moveFailed": "移动课程失败",
     "emptyFolderHint": "这个文件夹还是空的",
-    "backToAllCourses": "返回全部课程"
+    "backToAllCourses": "返回全部课程",
+    "emptyLibraryHint": "还没有课程——在上方创建，或导入一个课程。"
   },
   "upload": {
     "pdfSizeLimit": "支持最大50MB的PDF文件",

lib/i18n/locales/zh-TW.json

@@ -854,7 +854,7 @@
     "searchPlaceholder": "搜尋課程...",
     "newFolderTitle": "新建文件夹",
     "newFolderDesc": "把课程按主题或用途归类，方便查找。",
-    "newFolderInline": "新建文件夹…",
+    "newFolderInline": "新增資料夾",
     "folderNameLabel": "文件夹名称",
     "folderNamePlaceholder": "例如：数学、英语、专业课",
     "folderNameHint": "中英文均可，空格计入。",
@@ -862,8 +862,8 @@
     "folderCountLimit": "文件夹数量已达上限",
     "folderWidth": "宽度 {{width}}/{{max}}",
     "folderCreate": "创建",
-    "folderBadge": "文件夹",
-    "folderCourseCountUnit": "门课程",
+    "folderBadge": "資料夾",
+    "folderCourseCountUnit": "門課程",
     "deleteFolderTitle": "删除文件夹「{{name}}」",
     "deleteFolderEmptyDesc": "这是一个空文件夹，删除后不可恢复。",
     "deleteFolderDesc": "这个文件夹里有 {{count}} 门课程，请选择课程的处理方式。",
@@ -872,16 +872,17 @@
     "deleteFolderRemoveTitle": "连课程一起移出「我的课程」",
     "deleteFolderRemoveDesc": "课程不再出现在我的课程，对话记录一并清除，不可恢复。",
     "deleteFolderRemoveAction": "移出并删除",
-    "moveToFolder": "移动到文件夹",
-    "moveToFolderLabel": "移动到…",
-    "ungrouped": "未分组",
-    "searchResults": "搜索结果",
-    "folderCreateFailed": "创建文件夹失败",
-    "folderRenameFailed": "重命名文件夹失败",
-    "folderDeleteFailed": "删除文件夹失败",
-    "moveFailed": "移动课程失败",
-    "emptyFolderHint": "这个文件夹还是空的",
-    "backToAllCourses": "返回全部课程"
+    "moveToFolder": "移動到資料夾",
+    "moveToFolderLabel": "移動到資料夾",
+    "ungrouped": "未分類",
+    "searchResults": "搜尋結果",
+    "folderCreateFailed": "建立資料夾失敗",
+    "folderRenameFailed": "重新命名資料夾失敗",
+    "folderDeleteFailed": "刪除資料夾失敗",
+    "moveFailed": "移動課程失敗",
+    "emptyFolderHint": "這個資料夾是空的",
+    "backToAllCourses": "返回全部課程",
+    "emptyLibraryHint": "還沒有課程——在上方建立，或匯入一個課程。"
   },
   "upload": {
     "pdfSizeLimit": "支援最大50MB的PDF檔案",

lib/utils/stage-storage.ts

@@ -928,37 +928,43 @@ function assertFolderName(name: string, existing: FolderRecord[], currentId?: st
 /**
  * Create a folder. `order` is placed after the current maximum so new folders
  * land at the end of the list. Validates the name (width + uniqueness) at the
- * storage boundary.
+ * storage boundary, with the read-check-write inside a read-write transaction
+ * so two tabs cannot both pass the duplicate check before either write commits.
  */
 export async function createFolder(name: string): Promise<FolderRecord> {
   const now = Date.now();
-  const existing = await db.folders.toArray();
-  assertFolderName(name, existing);
-  const order = existing.reduce((max, folder) => Math.max(max, folder.order), -1) + 1;
-  const folder: FolderRecord = {
-    id: nanoid(),
-    name: name.trim(),
-    order,
-    createdAt: now,
-    updatedAt: now,
-  };
-  await db.folders.put(folder);
-  log.info(`Created folder "${name}" (${folder.id})`);
-  return folder;
+  return db.transaction('rw', db.folders, async () => {
+    const existing = await db.folders.toArray();
+    assertFolderName(name, existing);
+    const order = existing.reduce((max, folder) => Math.max(max, folder.order), -1) + 1;
+    const folder: FolderRecord = {
+      id: nanoid(),
+      name: name.trim(),
+      order,
+      createdAt: now,
+      updatedAt: now,
+    };
+    await db.folders.put(folder);
+    log.info(`Created folder "${name}" (${folder.id})`);
+    return folder;
+  });
 }
 
 /**
  * Rename a folder. Validates the name (width + uniqueness excluding itself) at
- * the storage boundary, so the UI invariant cannot be bypassed.
+ * the storage boundary, with the read-check-write inside a read-write
+ * transaction so the UI invariant cannot be bypassed or raced across tabs.
  */
 export async function renameFolder(id: string, name: string): Promise<void> {
   const now = Date.now();
-  const existing = await db.folders.toArray();
-  assertFolderName(name, existing, id);
-  const folder = existing.find((f) => f.id === id);
-  if (!folder) throw new Error(`Folder not found: ${id}`);
-  await db.folders.put({ ...folder, name: name.trim(), updatedAt: now });
-  log.info(`Renamed folder ${id} to "${name}"`);
+  await db.transaction('rw', db.folders, async () => {
+    const existing = await db.folders.toArray();
+    assertFolderName(name, existing, id);
+    const folder = existing.find((f) => f.id === id);
+    if (!folder) throw new Error(`Folder not found: ${id}`);
+    await db.folders.put({ ...folder, name: name.trim(), updatedAt: now });
+    log.info(`Renamed folder ${id} to "${name}"`);
+  });
 }
 
 export type DeleteFolderMode = 'ungroup' | 'remove';