Make backup wait for the server refresh and fail when it fails (closes #99)

lib.backup() refreshed through the background loop's refresh, which returns
at once when one is already running and swallows a failure, so a backup
could run on the previous file list, or on an empty cache, and exit 0. It
now uses the refresh fresh() uses: it joins a running refresh or starts
one, and rejects before touching any file when it fails. The CLI's error
wrapper prints that as one line and exits 1.

Model: opus-5-5

src/library/index.ts

@@ -538,11 +538,13 @@ export class Library {
     }
 
     // Back up every in-scope file to `downloadDirectory` in the historical
-    // on-disk layout, with a durable failure ledger (issue #51). Refreshes
-    // first, fetches pending originals (and optional thumbnails) through the
-    // content cache and pools, then rebuilds the derived symlink/JSON views
-    // from the model. Throws before any network work when no download directory
-    // is available or no content cache backs the originals it must fetch.
+    // on-disk layout, with a durable failure ledger (issue #51). Waits for a
+    // completed refresh first, as `fresh()` does, joining one already running,
+    // and rejects before touching any file when it fails. Then fetches pending
+    // originals (and optional thumbnails) through the content cache and pools,
+    // and rebuilds the derived symlink/JSON views from the model. Throws before
+    // any network work when no download directory is available or no content
+    // cache backs the originals it must fetch.
     backup(opts?: BackupOptions): Promise<BackupResult> {
         const downloadDirectory =
             opts?.downloadDirectory ?? this.downloadDirectory;
@@ -566,7 +568,7 @@ export class Library {
         const cache = this.cache;
         return runBackup(
             {
-                refresh: () => this.runRefresh(),
+                refresh: () => this.refreshNow(),
                 listCollections: () => this.store.listCollections(),
                 listFiles: (id) => this.store.listFiles(id),
                 original: (fileID) => cache!.original(fileID),