diff --git a/backend/src/services/dailyInventoryScreenshot.js b/backend/src/services/dailyInventoryScreenshot.js
index 594ade8..85623b3 100644
--- a/backend/src/services/dailyInventoryScreenshot.js
+++ b/backend/src/services/dailyInventoryScreenshot.js
@@ -13,7 +13,10 @@
 const fs = require('fs');
 const os = require('os');
 const path = require('path');
+const crypto = require('crypto');
 const jwt = require('jsonwebtoken');
+const bcrypt = require('bcryptjs');
+const database = require('../config/database');
 const { uploadFileToDefaultS3 } = require('./objectStorage');
 
 const TIMEZONE = 'Asia/Shanghai';
@@ -22,14 +25,24 @@ const PAGE_PATH = '/planning/operation/daily-inventory';
 const DEFAULT_BASE_URL = 'https://ck.yydd.ai';
 // 页面首次加载要扫订单明细，约 15~20 秒，等待上限给到 3 分钟
 const PAGE_READY_TIMEOUT_MS = 3 * 60 * 1000;
-const SCREENSHOT_SERVICE_USER = Object.freeze({
-  sub: 'daily-inventory-screenshot-bot',
-  username: 'daily_inventory_screenshot_bot',
-  name: '每日进销存截图服务',
-  role: 'admin',
-  authSource: 'service',
-  allowedPageKeys: [],
-});
+/**
+ * 截图专用服务账号
+ *
+ * 页面启动时会调用 /api/auth/verify，该接口要求令牌的 sub 必须是系统库 users 表中
+ * 真实且 active 的用户；仅签名合法但用户不存在的令牌会被判定为未登录并跳转登录页，
+ * 截图也就拿不到任何数据。因此这里不使用凭空捏造的身份，而是在系统库维护一个
+ * 仅供服务端使用的专用账号，令牌以该账号的 id 作为 sub。
+ *
+ * 该账号只以服务端签发的短时效令牌方式使用：密码哈希是随机值且永不对外，
+ * 任何人无法通过密码登录；删除该行即可彻底回收。
+ */
+const SERVICE_USERNAME = String(
+  process.env.DAILY_INVENTORY_SCREENSHOT_USERNAME || 'daily_inventory_screenshot_bot'
+).trim().slice(0, 50) || 'daily_inventory_screenshot_bot';
+const SERVICE_NAME = '每日进销存截图服务';
+const SERVICE_EMAIL = `${SERVICE_USERNAME}@service.local`;
+
+let cachedServiceUserId = null;
 
 const EXPAND_CSS = `
 .ant-table-body, .ant-table-content, .ant-table-container { max-height: none !important; overflow: visible !important; }
@@ -71,14 +84,72 @@ function resolvePageUrl() {
   return `${resolveBaseUrl()}${PAGE_PATH}`;
 }
 
+/** 清空服务账号 id 缓存（账号被重建或测试时刷新用） */
+function resetScreenshotServiceUserCache() {
+  cachedServiceUserId = null;
+}
+
+/** 生成一个无法用于登录的密码哈希（随机串无人知晓，仅满足字段非空约束） */
+function buildUnusablePasswordHash() {
+  return bcrypt.hash(crypto.randomBytes(32).toString('hex'), 10);
+}
+
+/**
+ * 确保系统库存在截图专用服务账号，并返回其 id。
+ * 只维护 auth_source='service' 的本服务账号，不触碰任何人工账号。
+ */
+async function ensureScreenshotServiceUser() {
+  if (cachedServiceUserId) return cachedServiceUserId;
+
+  const rows = await database.local.query(
+    'SELECT id, role, status FROM users WHERE username = ? LIMIT 1',
+    [SERVICE_USERNAME]
+  );
+  let user = rows[0];
+
+  if (!user) {
+    const created = await database.local.insert('users', {
+      username: SERVICE_USERNAME,
+      password_hash: await buildUnusablePasswordHash(),
+      name: SERVICE_NAME,
+      email: SERVICE_EMAIL,
+      role: 'admin',
+      status: 'active',
+      auth_source: 'service',
+    });
+    user = { id: created.insertId, role: 'admin', status: 'active' };
+  } else if (user.status !== 'active' || user.role !== 'admin') {
+    await database.local.query(
+      "UPDATE users SET role = 'admin', status = 'active', auth_source = 'service' WHERE id = ? AND auth_source = 'service'",
+      [user.id]
+    );
+  }
+
+  cachedServiceUserId = Number(user.id);
+  return cachedServiceUserId;
+}
+
 /**
  * 签发截图专用短时效令牌。
- * 只包含页面鉴权必需的最小声明，不含任何用户凭据或密钥。
+ * sub 为系统库中的专用服务账号 id，令牌只写入浏览器 localStorage，
+ * 不会出现在截图地址、日志或接口响应里，也不含任何密钥。
  */
-function signScreenshotToken() {
+async function signScreenshotToken() {
   const secret = process.env.CUBEJS_SECRET;
-  if (!secret) throw new Error('缺少 CUBEJS_SECRET，无法签发截图文身份令牌');
-  return jwt.sign({ ...SCREENSHOT_SERVICE_USER }, secret, { expiresIn: '15m' });
+  if (!secret) throw new Error('缺少 CUBEJS_SECRET，无法签发截图身份令牌');
+  const userId = await ensureScreenshotServiceUser();
+  return jwt.sign(
+    {
+      sub: String(userId),
+      username: SERVICE_USERNAME,
+      name: SERVICE_NAME,
+      role: 'admin',
+      authSource: 'service',
+      allowedPageKeys: [],
+    },
+    secret,
+    { expiresIn: '15m' }
+  );
 }
 
 /** 截图存放的临时文件（不落业务目录，上传后立即删除） */
@@ -147,7 +218,7 @@ async function waitForPageReady(page) {
 async function captureAndUploadDailyInventory(options = {}) {
   const now = options.now ? new Date(options.now) : new Date();
   const { bizDate, dateKey, timeKey } = chinaTimeParts(now);
-  const token = signScreenshotToken();
+  const token = await signScreenshotToken();
   const pageUrl = resolvePageUrl();
 
   const browser = await launchBrowser();
@@ -208,9 +279,13 @@ module.exports = {
   DEFAULT_BASE_URL,
   PAGE_PATH,
   PAGE_READY_TIMEOUT_MS,
+  SERVICE_NAME,
+  SERVICE_USERNAME,
   TIMEZONE,
   captureAndUploadDailyInventory,
   chinaTimeParts,
+  ensureScreenshotServiceUser,
+  resetScreenshotServiceUserCache,
   resolveBaseUrl,
   resolvePageUrl,
   signScreenshotToken,
diff --git a/backend/test/dailyInventoryNotification.test.js b/backend/test/dailyInventoryNotification.test.js
index 941c05c..852cdca 100644
--- a/backend/test/dailyInventoryNotification.test.js
+++ b/backend/test/dailyInventoryNotification.test.js
@@ -164,3 +164,78 @@ test('withRetry 超过次数后抛出最后一次错误', async () => {
   );
   assert.equal(calls, 3);
 });
+
+// ── 截图身份：必须使用系统库中真实存在的服务账号 ──────────────
+test('ensureScreenshotServiceUser 账号不存在时创建，存在时复用 id', async () => {
+  const database = require('../src/config/database');
+  const screenshot = require('../src/services/dailyInventoryScreenshot');
+  const original = database.local;
+  const calls = { select: 0, insert: 0, update: 0 };
+  let existing = null;
+
+  database.local = {
+    async query(sql, params) {
+      if (String(sql).startsWith('SELECT id, role, status FROM users')) {
+        calls.select += 1;
+        return existing ? [existing] : [];
+      }
+      calls.update += 1;
+      return { affectedRows: 1 };
+    },
+    async insert(_table, data) {
+      calls.insert += 1;
+      assert.equal(data.role, 'admin');
+      assert.equal(data.status, 'active');
+      assert.equal(data.auth_source, 'service');
+      assert.ok(String(data.password_hash || '').length > 20, '密码哈希不能为空');
+      existing = { id: 4242, role: data.role, status: data.status };
+      return { insertId: 4242 };
+    },
+  };
+
+  try {
+    screenshot.resetScreenshotServiceUserCache();
+    const created = await screenshot.ensureScreenshotServiceUser();
+    assert.equal(created, 4242);
+    assert.equal(calls.insert, 1);
+    assert.equal(calls.select, 1);
+
+    // 第二次调用命中缓存，不再查库
+    assert.equal(await screenshot.ensureScreenshotServiceUser(), 4242);
+    assert.equal(calls.select, 1);
+  } finally {
+    database.local = original;
+    screenshot.resetScreenshotServiceUserCache();
+  }
+});
+
+test('signScreenshotToken 的 sub 指向服务账号 id 且通过签名校验', async () => {
+  const database = require('../src/config/database');
+  const screenshot = require('../src/services/dailyInventoryScreenshot');
+  const jwt = require('jsonwebtoken');
+  const original = database.local;
+  const originalSecret = process.env.CUBEJS_SECRET;
+  process.env.CUBEJS_SECRET = originalSecret || 'test-secret-for-unit';
+
+  database.local = {
+    async query() {
+      return [{ id: 99, role: 'admin', status: 'active' }];
+    },
+    async insert() {
+      throw new Error('不应在账号已存在时插入');
+    },
+  };
+
+  try {
+    screenshot.resetScreenshotServiceUserCache();
+    const token = await screenshot.signScreenshotToken();
+    const payload = jwt.verify(token, process.env.CUBEJS_SECRET || 'test-secret');
+    assert.equal(payload.sub, '99');
+    assert.equal(payload.role, 'admin');
+    assert.equal(payload.authSource, 'service');
+  } finally {
+    database.local = original;
+    process.env.CUBEJS_SECRET = originalSecret;
+    screenshot.resetScreenshotServiceUserCache();
+  }
+});