fix(library): keep the shell the deploy replaced out of a failed navigation, and say when another tab holds the library open

docker/frontend/src/Library.tsx

@@ -20,6 +20,7 @@ import {
   listEditedIds,
   listFolders,
   normPath,
+  onLibraryBlocked,
   pickFolder,
   readPhotoFile,
   readPhotos,
@@ -376,6 +377,15 @@ function Catalogue() {
   // the folders and cannot tell whether the remembered subfolder still exists.
   const [loaded, setLoaded] = useState(false);
 
+  // Whether another tab still holds the library database at the version it was
+  // opened with — a tab left open across a build. Nothing can be read until it
+  // goes, and the screen would otherwise sit blank with no reason on it.
+  const [libraryBlocked, setLibraryBlocked] = useState(false);
+  useEffect(() => {
+    onLibraryBlocked(setLibraryBlocked);
+    return () => onLibraryBlocked(null);
+  }, []);
+
   // The folder the catalogue is copied into, and whether the browser is still
   // letting this page write to it — which it stops doing when the tab closes, so
   // the row below says so rather than letting a write fail quietly. The ref is
@@ -1614,6 +1624,12 @@ function Catalogue() {
               ) : null}
             </div>
 
+            {libraryBlocked ? (
+              <p className="hint adm-note" data-key="lib-blocked">
+                {t('lib.blocked')}
+              </p>
+            ) : null}
+
             {/* The folders are on their way in for as long as the catalogue behind
                 them is being read back, and a screen that says there is no folder
                 before it has looked is a screen that says it every visit. */}

docker/frontend/src/engine/library.ts

@@ -213,9 +213,21 @@ async function migrateLegacyDatabase(db: IDBDatabase): Promise<void> {
 
 let dbPromise: Promise<IDBDatabase> | null = null;
 
+// One library database per browser, so every tab shares it — and a tab left open
+// across a build holds it at the version it was opened with. The browser answers
+// the newer tab's open with silence until that tab goes: no error, no rows, no
+// note, a LIBRARY that has simply not loaded and never says why. The wait is
+// reported instead, and it ends by itself when the other tab is closed or reloaded.
+let blockedSink: ((blocked: boolean) => void) | null = null;
+
+export function onLibraryBlocked(fn: ((blocked: boolean) => void) | null): void {
+  blockedSink = fn;
+}
+
 function openDb(): Promise<IDBDatabase> {
   dbPromise ??= new Promise<IDBDatabase>((resolve, reject) => {
     const req = indexedDB.open(DB_NAME, DB_VERSION);
+    req.onblocked = () => blockedSink?.(true);
     req.onupgradeneeded = () => {
       const db = req.result;
       if (!db.objectStoreNames.contains(FOLDERS)) db.createObjectStore(FOLDERS, { keyPath: 'name' });
@@ -230,6 +242,7 @@ function openDb(): Promise<IDBDatabase> {
       if (!db.objectStoreNames.contains(EDITS)) db.createObjectStore(EDITS, { keyPath: 'photoId' });
     };
     req.onsuccess = () => {
+      blockedSink?.(false);
       const db = req.result;
       void migrateLegacyDatabase(db).then(() => resolve(db));
     };

docker/frontend/src/i18n/en.ts

@@ -296,6 +296,8 @@ export const en: Dict = {
   'lib.scanned': 'Scanned {folder}: {added}/{total} new frames.',
   'lib.empty': 'Nothing in this folder yet.',
   'lib.noFolders': 'No folder yet. Hit ADD FOLDER and pick a photo folder on this machine.',
+  'lib.blocked':
+    'Another tab of this app is holding the library open from an older build. Close that tab, or reload it, and this one picks the library up.',
   'lib.missing': 'Could not open {name} — the file has been moved or deleted.',
   'lib.failed': 'That folder could not be read.',
   'lib.unsupported':

docker/frontend/src/i18n/vi.ts

@@ -309,6 +309,8 @@ export const vi = {
   'lib.scanned': 'Đã quét {folder}: {added}/{total} ảnh mới.',
   'lib.empty': 'Chưa có ảnh nào trong thư mục này.',
   'lib.noFolders': 'Chưa có thư mục nào. Bấm THÊM THƯ MỤC để chọn một thư mục ảnh trên máy.',
+  'lib.blocked':
+    'Một tab khác của ứng dụng đang giữ thư viện ở bản cũ hơn. Hãy đóng tab đó, hoặc tải lại nó, để tab này mở được thư viện.',
   'lib.missing': 'Không mở được {name} — tệp đã bị di chuyển hoặc xoá.',
   'lib.failed': 'Không đọc được thư mục này.',
   'lib.unsupported':