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/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));
     };