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

test/cli/backup.test.ts

@@ -625,6 +625,93 @@ describe("lib.backup", () => {
     });
 });
 
+// Every refresh fails, as with an expired session or no network.
+class FailingClient extends MockClient {
+    override async collectionsSince(): Promise<CollectionsPage> {
+        throw new Error("HTTP 401 from server");
+    }
+}
+
+// Holds its refresh open until `release()` is called, then reports a third
+// album, so a backup can be started while that refresh is still running.
+class HeldClient extends MockClient {
+    release!: () => void;
+    private held = new Promise<void>((resolve) => {
+        this.release = resolve;
+    });
+    override async collectionsSince(): Promise<CollectionsPage> {
+        await this.held;
+        return {
+            collections: [collection(3, "Later")],
+            deleted: [],
+            cursor: 2,
+        };
+    }
+    override async filesSince(args: {
+        collectionID: number;
+    }): Promise<FilesPage> {
+        if (args.collectionID !== 3) return super.filesSince(args);
+        return { files: [file(300, 3, "late.jpg")], deleted: [], cursor: 2 };
+    }
+}
+
+// Fill the library cache on disk, so the next open starts its refresh in the
+// background instead of waiting for it.
+const fillCache = async (): Promise<void> => {
+    const lib = await openLibrary(stubSource());
+    await lib.close();
+};
+
+describe("the refresh before a backup", () => {
+    it("waits for a refresh already running and backs up what it found", async () => {
+        await fillCache();
+        const client = new HeldClient();
+        const lib = await openLibrary(stubSource(), client);
+        const outDir = join(root, "backup");
+
+        const backup = lib.backup({ downloadDirectory: outDir });
+        client.release();
+        const result = await backup;
+
+        expect(result.totalFiles).toBe(4);
+        expect(existsSync(join(outDir, "originals", "300.jpg"))).toBe(true);
+        await lib.close();
+    });
+
+    it("fails before any download when the refresh fails, leaving failures.json as it was", async () => {
+        await fillCache();
+        const outDir = join(root, "backup");
+        seedLedger(outDir, 100, "beach.jpg");
+        const ledgerPath = join(outDir, "failures.json");
+        const ledgerBefore = readFileSync(ledgerPath, "utf-8");
+        const source = stubSource();
+        const lib = await openLibrary(source, new FailingClient());
+
+        await expect(lib.backup({ downloadDirectory: outDir })).rejects.toThrow(
+            "HTTP 401 from server",
+        );
+
+        expect(source.originalCalls).toBe(0);
+        expect(readFileSync(ledgerPath, "utf-8")).toBe(ledgerBefore);
+        expect(existsSync(join(outDir, "originals"))).toBe(false);
+        await lib.close();
+    });
+
+    it("fails when the refresh fails on an empty cache, instead of backing up nothing", async () => {
+        const source = stubSource();
+        const lib = await openLibrary(source, new FailingClient());
+        const outDir = join(root, "backup");
+
+        await expect(lib.backup({ downloadDirectory: outDir })).rejects.toThrow(
+            "HTTP 401 from server",
+        );
+
+        expect(source.originalCalls).toBe(0);
+        expect(existsSync(outDir)).toBe(false);
+        await lib.close();
+    });
+});
+
 // The album folders under collections/, driven through `runBackup` with a
 // stand-in library whose albums a test changes between runs.
 describe("backup album folders", () => {