diff --git a/sync-server/docker-compose.caddy.yml b/sync-server/docker-compose.caddy.yml
index 647ed4b..657d26e 100644
--- a/sync-server/docker-compose.caddy.yml
+++ b/sync-server/docker-compose.caddy.yml
@@ -13,7 +13,10 @@ services:
     # 无需 ports 映射：Caddy 通过容器网络按服务名直连（footprints-sync:8788）
     volumes:
       - ./data:/data
-      - ./www:/app/www:ro   # 前端直读仓库目录：git pull 即生效，无需重建镜像
+      - ./www:/app/www:ro            # 前端直读仓库目录：git pull 即生效，无需重建镜像
+      - ./src:/app/src:ro            # 后端源码直读（零依赖纯 .mjs）
+      - ./schema.sql:/app/schema.sql:ro
+      - ../app/server/db.mjs:/app/src/app-commands.mjs:ro   # 命令层以仓库数据层为准
     environment:
       - REGISTER_ENABLED=true
       - INVITE_CODE=please-change-me   # 多用户：注册须携带此邀请码（留空则不校验）
diff --git a/sync-server/src/auth.mjs b/sync-server/src/auth.mjs
index 2886bd5..0870e93 100644
--- a/sync-server/src/auth.mjs
+++ b/sync-server/src/auth.mjs
@@ -2,10 +2,10 @@
 import crypto from 'node:crypto';
 import { getDb } from './db.mjs';
 
-export function register({ username, password, device_name, invite_code }) {
+export function register({ username, password, device_name, invite_code, seed }) {
   const d = getDb();
   // 多用户管控：管理员颁发邀请码；env INVITE_CODE 作为静态兜底
-  const maxUsers = Number(process.env.MAX_USERS || 0);
+  const maxUsers = seed ? 0 : Number(process.env.MAX_USERS || 0); // seed 播种不受名额限制
   if (maxUsers > 0) {
     const cnt = d.prepare('SELECT COUNT(*) AS c FROM users').get().c;
     if (cnt >= maxUsers) throw new Error('注册名额已满，请联系管理员');
@@ -14,16 +14,18 @@ export function register({ username, password, device_name, invite_code }) {
   let isAdmin = 0;
   if (userCount === 0) {
     isAdmin = 1; // 首位注册者自动成为管理员
+  } else if (seed) {
+    // 内置演示账号播种：不要求邀请码
   } else {
     const code = String(invite_code || '').trim().toUpperCase();
-    if (code) {
-      const row = d.prepare('SELECT id, valid FROM invite_codes WHERE code=?').get(code);
-      if (!row || !row.valid) throw new Error('邀请码无效或已使用');
+    const envCode = String(process.env.INVITE_CODE || '').trim().toUpperCase();
+    const row = code ? d.prepare('SELECT id, valid FROM invite_codes WHERE code=?').get(code) : null;
+    if (row && row.valid) {
       var __usedInviteId = row.id; // eslint-disable-line no-var
-    } else if (process.env.INVITE_CODE && invite_code === process.env.INVITE_CODE) {
-      // 静态兜底码
+    } else if (code && envCode && code === envCode) {
+      // 静态兜底码（env INVITE_CODE），与动态邀请码等价
     } else {
-      throw new Error('需要邀请码，请联系管理员');
+      throw new Error(code ? '邀请码无效或已使用' : '需要邀请码，请联系管理员');
     }
   }
   if (!/^[a-zA-Z0-9_-]{3,32}$/.test(username || '')) throw new Error('用户名需为 3-32 位字母数字-_');
diff --git a/sync-server/src/index.mjs b/sync-server/src/index.mjs
index 17a3d5c..f597cfa 100644
--- a/sync-server/src/index.mjs
+++ b/sync-server/src/index.mjs
@@ -209,12 +209,17 @@ function readJson(req) {
 
 getDb();
 
-// 种子演示账号（demo / demo1234，管理员权限），便于部署后立即可用
+// 种子演示账号（demo / demo1234）；seed 标记绕过邀请码/名额校验，失败原因打出日志
 try {
-  const { register } = await import('./auth.mjs');
-  register({ username: 'demo', password: 'demo1234', device_name: 'seed' });
-  console.log('[footprints-sync] demo 账号已就绪 (demo / demo1234)');
-} catch { /* 已存在则跳过 */ }
+  const d = getDb();
+  if (!d.prepare('SELECT 1 FROM users WHERE username=?').get('demo')) {
+    const { register } = await import('./auth.mjs');
+    register({ username: 'demo', password: 'demo1234', device_name: 'seed-demo', seed: true });
+    console.log('[footprints-sync] demo 账号已创建 (demo / demo1234)');
+  } else {
+    console.log('[footprints-sync] demo 账号已存在 (demo / demo1234)');
+  }
+} catch (e) { console.log('[footprints-sync] demo 种子跳过:', e.message); }
 
 server.listen(PORT, '0.0.0.0', () => {
   console.log('[footprints-sync] listening on 0.0.0.0:' + PORT);