diff --git a/packages/cli/src/__tests__/book-backup.test.ts b/packages/cli/src/__tests__/book-backup.test.ts
new file mode 100644
index 00000000..9e2c8cc1
--- /dev/null
+++ b/packages/cli/src/__tests__/book-backup.test.ts
@@ -0,0 +1,165 @@
+import { access, mkdir, mkdtemp, readFile, writeFile } from "node:fs/promises";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { beforeEach, describe, expect, it, vi } from "vitest";
+import { createBookBackup, listBookBackups, restoreBookBackup } from "../book-backup.js";
+
+const logMock = vi.fn();
+const logErrorMock = vi.fn();
+let projectRoot = "";
+
+vi.mock("../utils.js", async (importOriginal) => ({
+  ...(await importOriginal<typeof import("../utils.js")>()),
+  findProjectRoot: () => projectRoot,
+  log: (message: string) => logMock(message),
+  logError: (message: string) => logErrorMock(message),
+}));
+
+async function exists(path: string): Promise<boolean> {
+  return access(path).then(() => true).catch(() => false);
+}
+
+async function setupBook(bookId: string): Promise<string> {
+  projectRoot = await mkdtemp(join(tmpdir(), "inkos-book-backup-"));
+  const bookDir = join(projectRoot, "books", bookId);
+  await mkdir(join(bookDir, "chapters"), { recursive: true });
+  await mkdir(join(bookDir, "story"), { recursive: true });
+  await writeFile(join(bookDir, "book.json"), JSON.stringify({ id: bookId, title: bookId, language: "zh" }), "utf-8");
+  await writeFile(join(bookDir, "chapters", "0001_起风.md"), "第一章原文。", "utf-8");
+  await writeFile(join(bookDir, "story", "current_state.md"), "原始状态", "utf-8");
+  return bookDir;
+}
+
+const fixedClock = (iso: string) => () => new Date(iso);
+
+describe("book backup module", () => {
+  it("snapshots the whole book directory into .inkos/backups/<bookId>/<stamp>/", async () => {
+    const bookDir = await setupBook("backbook");
+
+    const result = await createBookBackup(projectRoot, "backbook", { now: fixedClock("2026-07-15T08:12:33Z") });
+
+    expect(result.backupId).toBe("20260715-081233");
+    const backupDir = join(projectRoot, ".inkos", "backups", "backbook", "20260715-081233");
+    await expect(readFile(join(backupDir, "chapters", "0001_起风.md"), "utf-8")).resolves.toBe("第一章原文。");
+    await expect(readFile(join(backupDir, "story", "current_state.md"), "utf-8")).resolves.toBe("原始状态");
+    // The original book stays in place.
+    await expect(exists(join(bookDir, "book.json"))).resolves.toBe(true);
+  });
+
+  it("produces distinct ids for two backups taken at the same clock instant", async () => {
+    await setupBook("twinbook");
+    const now = fixedClock("2026-07-15T08:12:33Z");
+
+    const first = await createBookBackup(projectRoot, "twinbook", { now });
+    const second = await createBookBackup(projectRoot, "twinbook", { now });
+
+    expect(first.backupId).toBe("20260715-081233");
+    expect(second.backupId).toBe("20260715-081233-2");
+  });
+
+  it("lists backups newest first", async () => {
+    await setupBook("listbook");
+    await createBookBackup(projectRoot, "listbook", { now: fixedClock("2026-07-14T10:00:00Z") });
+    await createBookBackup(projectRoot, "listbook", { now: fixedClock("2026-07-15T10:00:00Z") });
+
+    const backups = await listBookBackups(projectRoot, "listbook");
+
+    expect(backups.map((b) => b.id)).toEqual(["20260715-100000", "20260714-100000"]);
+    expect(backups[0]?.createdAt).toMatch(/^\d{4}-\d{2}-\d{2}T/);
+  });
+
+  it("returns an empty list for a book without backups", async () => {
+    await setupBook("nobackups");
+    await expect(listBookBackups(projectRoot, "nobackups")).resolves.toEqual([]);
+  });
+
+  it("restores a backup and auto-backs-up the current state first", async () => {
+    const bookDir = await setupBook("restorebook");
+    const backup = await createBookBackup(projectRoot, "restorebook", { now: fixedClock("2026-07-15T08:00:00Z") });
+
+    await writeFile(join(bookDir, "chapters", "0001_起风.md"), "改坏了的第一章。", "utf-8");
+    await writeFile(join(bookDir, "chapters", "0002_多余.md"), "多写的一章。", "utf-8");
+
+    const result = await restoreBookBackup(projectRoot, "restorebook", backup.backupId, {
+      now: fixedClock("2026-07-15T09:00:00Z"),
+    });
+
+    expect(result.restoredFrom).toBe("20260715-080000");
+    expect(result.preRestoreBackupId).toBe("20260715-090000-pre-restore");
+
+    // Content is back to the backup point, including removal of extra files.
+    await expect(readFile(join(bookDir, "chapters", "0001_起风.md"), "utf-8")).resolves.toBe("第一章原文。");
+    await expect(exists(join(bookDir, "chapters", "0002_多余.md"))).resolves.toBe(false);
+
+    // The pre-restore auto-backup preserves the botched state.
+    const preRestoreDir = join(projectRoot, ".inkos", "backups", "restorebook", "20260715-090000-pre-restore");
+    await expect(readFile(join(preRestoreDir, "chapters", "0001_起风.md"), "utf-8")).resolves.toBe("改坏了的第一章。");
+    await expect(readFile(join(preRestoreDir, "chapters", "0002_多余.md"), "utf-8")).resolves.toBe("多写的一章。");
+  });
+
+  it("rejects backing up a book that does not exist", async () => {
+    await setupBook("realbook");
+    await expect(createBookBackup(projectRoot, "ghostbook")).rejects.toThrow(/not found/i);
+  });
+
+  it("rejects restoring an unknown backup id", async () => {
+    await setupBook("orphanbook");
+    await expect(restoreBookBackup(projectRoot, "orphanbook", "20990101-000000"))
+      .rejects.toThrow(/not found/i);
+  });
+
+  it("rejects backup ids containing path separators", async () => {
+    await setupBook("evilbook");
+    await expect(restoreBookBackup(projectRoot, "evilbook", "../../books/evilbook"))
+      .rejects.toThrow(/backup id/i);
+  });
+});
+
+describe("inkos book backup / restore commands", () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+  });
+
+  it("creates a backup, lists it, and restores it via the CLI", async () => {
+    const bookDir = await setupBook("cliflow");
+    const { bookCommand } = await import("../commands/book.js");
+
+    await bookCommand.parseAsync(["node", "book", "backup", "cliflow", "--json"], { from: "node" });
+    expect(logErrorMock).not.toHaveBeenCalled();
+    const created = JSON.parse(logMock.mock.calls.at(-1)?.[0] as string) as { backupId: string };
+    expect(created.backupId).toMatch(/^\d{8}-\d{6}/);
+
+    await bookCommand.parseAsync(["node", "book", "backup", "cliflow", "--list", "--json"], { from: "node" });
+    const listed = JSON.parse(logMock.mock.calls.at(-1)?.[0] as string) as {
+      backups: ReadonlyArray<{ id: string }>;
+    };
+    expect(listed.backups.map((b) => b.id)).toContain(created.backupId);
+
+    await writeFile(join(bookDir, "chapters", "0001_起风.md"), "改坏了。", "utf-8");
+
+    await bookCommand.parseAsync(["node", "book", "restore", "cliflow", created.backupId, "--json"], { from: "node" });
+    expect(logErrorMock).not.toHaveBeenCalled();
+    const restored = JSON.parse(logMock.mock.calls.at(-1)?.[0] as string) as {
+      restoredFrom: string;
+      preRestoreBackupId: string | null;
+    };
+    expect(restored.restoredFrom).toBe(created.backupId);
+    expect(restored.preRestoreBackupId).not.toBeNull();
+
+    await expect(readFile(join(bookDir, "chapters", "0001_起风.md"), "utf-8")).resolves.toBe("第一章原文。");
+  });
+
+  it("fails with exit code 1 when restoring a backup that does not exist", async () => {
+    await setupBook("clibroken");
+    const exitSpy = vi.spyOn(process, "exit").mockImplementation((() => undefined) as never);
+    try {
+      const { bookCommand } = await import("../commands/book.js");
+      await bookCommand.parseAsync(["node", "book", "restore", "clibroken", "20990101-000000"], { from: "node" });
+
+      expect(logErrorMock).toHaveBeenCalledWith(expect.stringContaining("not found"));
+      expect(exitSpy).toHaveBeenCalledWith(1);
+    } finally {
+      exitSpy.mockRestore();
+    }
+  });
+});
diff --git a/packages/cli/src/book-backup.ts b/packages/cli/src/book-backup.ts
new file mode 100644
index 00000000..ca87fcb2
--- /dev/null
+++ b/packages/cli/src/book-backup.ts
@@ -0,0 +1,132 @@
+import { access, cp, mkdir, readdir, rm, stat } from "node:fs/promises";
+import { join } from "node:path";
+
+export interface BookBackupInfo {
+  readonly id: string;
+  readonly createdAt: string;
+}
+
+export interface CreateBookBackupOptions {
+  /** Injectable clock so tests do not depend on real time. */
+  readonly now?: () => Date;
+  /** Appended to the backup id, e.g. "pre-restore". */
+  readonly suffix?: string;
+}
+
+export interface CreateBookBackupResult {
+  readonly bookId: string;
+  readonly backupId: string;
+  readonly path: string;
+}
+
+export interface RestoreBookBackupOptions {
+  readonly now?: () => Date;
+}
+
+export interface RestoreBookBackupResult {
+  readonly bookId: string;
+  readonly restoredFrom: string;
+  /** Auto-backup of the pre-restore state; null when the book directory did not exist. */
+  readonly preRestoreBackupId: string | null;
+}
+
+/**
+ * Whole-book backups live OUTSIDE books/ (at .inkos/backups/<bookId>/<backupId>/),
+ * so a backup never recursively contains other backups.
+ */
+export function bookBackupsDir(root: string, bookId: string): string {
+  return join(root, ".inkos", "backups", bookId);
+}
+
+export async function createBookBackup(
+  root: string,
+  bookId: string,
+  options: CreateBookBackupOptions = {},
+): Promise<CreateBookBackupResult> {
+  const bookDir = join(root, "books", bookId);
+  const bookInfo = await stat(bookDir).catch(() => null);
+  if (!bookInfo?.isDirectory()) {
+    throw new Error(`Book "${bookId}" not found at books/${bookId}/.`);
+  }
+
+  const backupsDir = bookBackupsDir(root, bookId);
+  await mkdir(backupsDir, { recursive: true });
+
+  const clock = options.now ?? (() => new Date());
+  const base = options.suffix ? `${formatStamp(clock())}-${options.suffix}` : formatStamp(clock());
+  let backupId = base;
+  for (let attempt = 2; await pathExists(join(backupsDir, backupId)); attempt += 1) {
+    backupId = `${base}-${attempt}`;
+  }
+
+  const backupPath = join(backupsDir, backupId);
+  await cp(bookDir, backupPath, { recursive: true });
+  return { bookId, backupId, path: backupPath };
+}
+
+export async function listBookBackups(
+  root: string,
+  bookId: string,
+): Promise<ReadonlyArray<BookBackupInfo>> {
+  const backupsDir = bookBackupsDir(root, bookId);
+  const entries = await readdir(backupsDir, { withFileTypes: true }).catch((error) => {
+    if ((error as { code?: unknown }).code === "ENOENT") {
+      return [];
+    }
+    throw error;
+  });
+
+  const backups = await Promise.all(
+    entries
+      .filter((entry) => entry.isDirectory())
+      .map(async (entry) => {
+        const info = await stat(join(backupsDir, entry.name));
+        return { id: entry.name, createdAt: info.mtime.toISOString() };
+      }),
+  );
+  // Backup ids start with a UTC timestamp, so a descending id sort is newest-first.
+  return backups.sort((a, b) => b.id.localeCompare(a.id));
+}
+
+export async function restoreBookBackup(
+  root: string,
+  bookId: string,
+  backupId: string,
+  options: RestoreBookBackupOptions = {},
+): Promise<RestoreBookBackupResult> {
+  // backupId comes from CLI input and is joined into a path — keep it a single
+  // safe path component.
+  if (!/^[A-Za-z0-9._-]+$/.test(backupId) || backupId === "." || backupId === "..") {
+    throw new Error(`Invalid backup id "${backupId}": a backup id must be a single directory name.`);
+  }
+
+  const backupPath = join(bookBackupsDir(root, bookId), backupId);
+  const backupInfo = await stat(backupPath).catch(() => null);
+  if (!backupInfo?.isDirectory()) {
+    throw new Error(
+      `Backup "${backupId}" not found for book "${bookId}". `
+      + `List available backups with: inkos book backup ${bookId} --list`,
+    );
+  }
+
+  const bookDir = join(root, "books", bookId);
+  const bookExists = await stat(bookDir).then((info) => info.isDirectory()).catch(() => false);
+  let preRestoreBackupId: string | null = null;
+  if (bookExists) {
+    const preRestore = await createBookBackup(root, bookId, { now: options.now, suffix: "pre-restore" });
+    preRestoreBackupId = preRestore.backupId;
+  }
+
+  await rm(bookDir, { recursive: true, force: true });
+  await cp(backupPath, bookDir, { recursive: true });
+
+  return { bookId, restoredFrom: backupId, preRestoreBackupId };
+}
+
+function formatStamp(date: Date): string {
+  return date.toISOString().slice(0, 19).replace(/[-:]/g, "").replace("T", "-");
+}
+
+async function pathExists(path: string): Promise<boolean> {
+  return access(path).then(() => true).catch(() => false);
+}
diff --git a/packages/cli/src/commands/book.ts b/packages/cli/src/commands/book.ts
index 10c7a9e0..0a3f2e3e 100644
--- a/packages/cli/src/commands/book.ts
+++ b/packages/cli/src/commands/book.ts
@@ -4,13 +4,17 @@ import { createInterface } from "node:readline";
 import { join, resolve } from "node:path";
 import { deriveBookIdFromTitle, normalizePlatformOrOther, PipelineRunner, StateManager, type BookConfig } from "@actalk/inkos-core";
 import {
+  formatBookBackupCreated,
+  formatBookBackupListEmpty,
   formatBookCreateCreated,
   formatBookCreateCreating,
   formatBookCreateFoundationReady,
   formatBookCreateLocation,
   formatBookCreateNextStep,
+  formatBookRestoreDone,
   resolveCliLanguage,
 } from "../localization.js";
+import { createBookBackup, listBookBackups, restoreBookBackup } from "../book-backup.js";
 import { loadConfig, buildPipelineConfig, findProjectRoot, resolveBookId, log, logError } from "../utils.js";
 
 export const bookCommand = new Command("book")
@@ -258,3 +262,78 @@ bookCommand
       process.exit(1);
     }
   });
+
+bookCommand
+  .command("backup")
+  .description("Snapshot the whole book directory into .inkos/backups/<book-id>/ (or list backups with --list)")
+  .argument("<book-id>", "Book ID")
+  .option("--list", "List existing backups instead of creating one")
+  .option("--json", "Output JSON")
+  .action(async (bookId: string, opts) => {
+    try {
+      const root = findProjectRoot();
+      // Backups must also work on broken books (e.g. corrupted book.json),
+      // so the output language follows the environment, not the book config.
+      const language = resolveCliLanguage();
+
+      if (opts.list) {
+        const backups = await listBookBackups(root, bookId);
+        if (opts.json) {
+          log(JSON.stringify({ bookId, backups }, null, 2));
+        } else if (backups.length === 0) {
+          log(formatBookBackupListEmpty(language, bookId));
+        } else {
+          for (const backup of backups) {
+            log(`  ${backup.id}  ${backup.createdAt}`);
+          }
+        }
+        return;
+      }
+
+      const result = await createBookBackup(root, bookId);
+      if (opts.json) {
+        log(JSON.stringify({ bookId, backupId: result.backupId }, null, 2));
+      } else {
+        log(formatBookBackupCreated(language, bookId, result.backupId));
+      }
+    } catch (e) {
+      if (opts.json) {
+        log(JSON.stringify({ error: String(e) }));
+      } else {
+        logError(`Failed to back up book: ${e}`);
+      }
+      process.exit(1);
+    }
+  });
+
+bookCommand
+  .command("restore")
+  .description("Restore a whole-book backup (the current book state is automatically backed up first)")
+  .argument("<book-id>", "Book ID")
+  .argument("<backup-id>", "Backup ID, see `inkos book backup <book-id> --list`")
+  .option("--json", "Output JSON")
+  .action(async (bookId: string, backupId: string, opts) => {
+    try {
+      const root = findProjectRoot();
+      const language = resolveCliLanguage();
+
+      const result = await restoreBookBackup(root, bookId, backupId);
+
+      if (opts.json) {
+        log(JSON.stringify(result, null, 2));
+      } else {
+        log(formatBookRestoreDone(language, {
+          bookId,
+          backupId: result.restoredFrom,
+          preRestoreBackupId: result.preRestoreBackupId,
+        }));
+      }
+    } catch (e) {
+      if (opts.json) {
+        log(JSON.stringify({ error: String(e) }));
+      } else {
+        logError(`Failed to restore book: ${e}`);
+      }
+      process.exit(1);
+    }
+  });
diff --git a/packages/cli/src/localization.ts b/packages/cli/src/localization.ts
index 78803bce..85be05ae 100644
--- a/packages/cli/src/localization.ts
+++ b/packages/cli/src/localization.ts
@@ -509,3 +509,36 @@ export function formatChapterDeleteDone(
     en: `Deleted chapter ${params.number} ${params.title}: chapter file kept at ${trashNote}; index and story state rolled back to chapter ${params.rolledBackTo}.`,
   });
 }
+
+export function formatBookBackupCreated(language: CliLanguage, bookId: string, backupId: string): string {
+  return localize(language, {
+    zh: `已备份 ${bookId} → .inkos/backups/${bookId}/${backupId}/`,
+    en: `Backed up ${bookId} → .inkos/backups/${bookId}/${backupId}/`,
+  });
+}
+
+export function formatBookBackupListEmpty(language: CliLanguage, bookId: string): string {
+  return localize(language, {
+    zh: `${bookId} 还没有备份。用 inkos book backup ${bookId} 创建一份。`,
+    en: `No backups for ${bookId} yet. Create one with: inkos book backup ${bookId}`,
+  });
+}
+
+export function formatBookRestoreDone(
+  language: CliLanguage,
+  params: { bookId: string; backupId: string; preRestoreBackupId: string | null },
+): string {
+  const preNote = params.preRestoreBackupId
+    ? localize(language, {
+        zh: `恢复前的状态已自动备份为 ${params.preRestoreBackupId}。`,
+        en: `The pre-restore state was automatically backed up as ${params.preRestoreBackupId}.`,
+      })
+    : localize(language, {
+        zh: "书目录当时不存在，未创建恢复前备份。",
+        en: "The book directory did not exist, so no pre-restore backup was created.",
+      });
+  return localize(language, {
+    zh: `已把 ${params.bookId} 恢复到备份 ${params.backupId}。${preNote}`,
+    en: `Restored ${params.bookId} to backup ${params.backupId}. ${preNote}`,
+  });
+}