diff --git a/README.md b/README.md
index 6882a0b..f22b158 100644
--- a/README.md
+++ b/README.md
@@ -108,7 +108,7 @@ Each family's latest generation only — the app's **Models** page lists every b
 
 ## Installation
 
-Every route installs the same `penguin` command: `penguin web` launches the full Web experience (multi-session chat, agent/skill/model management, usage stats, Trace observability, evaluation center; first login admin / penguin-2026 — change the password right after), and models are configured on the in-app Models page. The online installers bundle their own Node runtime — unpack and run; upgrades and reinstalls never touch your data.
+Every route installs the same `penguin` command: `penguin web` launches the full Web experience (multi-session chat, agent/skill/model management, usage stats, Trace observability, evaluation center; first login is `admin` with the initial password printed on the server's first start, of the form `penguin-1234` — change it right after), and models are configured on the in-app Models page. The online installers bundle their own Node runtime — unpack and run; upgrades and reinstalls never touch your data.
 
 ### 🐧 Linux (online install)
 
diff --git a/README.zh.md b/README.zh.md
index ca3f3c8..b446036 100644
--- a/README.zh.md
+++ b/README.zh.md
@@ -108,7 +108,7 @@ https://github.com/user-attachments/assets/aec49ae9-b743-467b-b247-37bedfeaa36e
 
 ## 安装
 
-每种方式装出的都是同一个 `penguin` 命令：`penguin web` 启动完整 Web 体验（多会话对话、Agent / 技能 / 模型管理、用量统计、轨迹观测、评估中心；首次登录 admin / penguin-2026，登录后请尽快修改密码），在应用内模型页配置模型后即可对话。在线安装器自带 Node 运行时，解压即用，升级与重装不触碰数据。
+每种方式装出的都是同一个 `penguin` 命令：`penguin web` 启动完整 Web 体验（多会话对话、Agent / 技能 / 模型管理、用量统计、轨迹观测、评估中心；首次登录使用 `admin`，初始密码在服务端首次启动时打印，形如 `penguin-1234`，登录后请尽快修改密码），在应用内模型页配置模型后即可对话。在线安装器自带 Node 运行时，解压即用，升级与重装不触碰数据。
 
 ### 🐧 Linux（在线安装）
 
diff --git a/install.ps1 b/install.ps1
index d6b993d..20dd2e6 100644
--- a/install.ps1
+++ b/install.ps1
@@ -442,5 +442,5 @@ if ($PathUpdateMessage) {
 Write-Host ""
 Write-Host "Get started:"
 Write-Host "  penguin --help    # all commands"
-Write-Host "  penguin web       # start the Web UI at http://127.0.0.1:7364 (initial login: admin / penguin-2026)"
+Write-Host "  penguin web       # start the Web UI at http://127.0.0.1:7364 (login: admin, initial password printed on first start)"
 Write-Host "  penguin server    # headless server (PORT / HOST to override)"
diff --git a/install.sh b/install.sh
index 8f55698..5fb8b93 100644
--- a/install.sh
+++ b/install.sh
@@ -441,5 +441,5 @@ fi
 echo ""
 echo "Get started:"
 echo "  penguin --help    # all commands"
-echo "  penguin web       # start the Web UI at http://127.0.0.1:7364 (initial login: admin / penguin-2026)"
+echo "  penguin web       # start the Web UI at http://127.0.0.1:7364 (login: admin, initial password printed on first start)"
 echo "  penguin server    # headless server (PORT / HOST to override)"
diff --git a/packages/docs/content/configuration.en.md b/packages/docs/content/configuration.en.md
index b0f0b4e..08f64e6 100644
--- a/packages/docs/content/configuration.en.md
+++ b/packages/docs/content/configuration.en.md
@@ -17,6 +17,7 @@ The CLI and the server automatically load a `.env` file from the working directo
 | `PENGUIN_WEB_DB` | Server SQLite database path | `<root>/web.db` |
 | `PENGUIN_WEB_DIST` | Front-end static assets directory | the npm server package falls back to its bundled web-dist |
 | `PENGUIN_PREVIEW_ORIGIN` | Origin that serves Workspace HTML previews, e.g. `https://preview.example.com` | unset — the loopback counterpart is derived per request |
+| `PENGUIN_SEED_ADMIN_PASSWORD` | Fixed initial password for the seeded built-in admin (automated tests / e2e) | unset — a random `penguin-<4 digits>` password is generated and printed once at seed time |
 | `PENGUIN_LANG` | CLI language (`en` / `zh`), set via `penguin config lang` | `en` |
 | `PENGUIN_UPDATE_CHECK` | `off` disables the web app's new-release check (the server's only outbound internet call) | enabled |
 
diff --git a/packages/docs/content/configuration.zh.md b/packages/docs/content/configuration.zh.md
index 2c0a599..7778014 100644
--- a/packages/docs/content/configuration.zh.md
+++ b/packages/docs/content/configuration.zh.md
@@ -17,6 +17,7 @@ CLI 与服务端启动时会自动加载工作目录下的 `.env` 文件。
 | `PENGUIN_WEB_DB` | 服务端 SQLite 数据库路径 | `<root>/web.db` |
 | `PENGUIN_WEB_DIST` | 前端静态资源目录 | npm 安装的服务端包回退到内置 web-dist |
 | `PENGUIN_PREVIEW_ORIGIN` | 提供 Workspace HTML 预览的独立源，如 `https://preview.example.com` | 未设置，按请求推导回环对应名 |
+| `PENGUIN_SEED_ADMIN_PASSWORD` | 固定内置管理员的种子初始密码（自动化测试 / e2e 使用） | 未设置，种子时随机生成 `penguin-<四位数字>` 并打印一次 |
 | `PENGUIN_LANG` | CLI 语言（`en` / `zh`），用 `penguin config lang` 设置 | `en` |
 | `PENGUIN_UPDATE_CHECK` | 设为 `off` 关闭 Web 应用的新版本检查（服务端唯一的对外网络请求） | 开启 |
 
diff --git a/packages/docs/content/quickstart.en.md b/packages/docs/content/quickstart.en.md
index fb12a52..8ce24af 100644
--- a/packages/docs/content/quickstart.en.md
+++ b/packages/docs/content/quickstart.en.md
@@ -30,7 +30,7 @@ penguin config model add --provider deepseek --model-id deepseek-v4-flash --api-
 penguin web
 ```
 
-The service runs at http://127.0.0.1:7364 and opens your browser (`--no-open` to skip). First login is `admin` / `penguin-2026` — change it right away. `penguin server` starts the same process headless.
+The service runs at http://127.0.0.1:7364 and opens your browser (`--no-open` to skip). First login is `admin` — the server prints the initial password (of the form `penguin-1234`) on first start; change it right away. `penguin server` starts the same process headless.
 
 ## One-shot run
 
diff --git a/packages/docs/content/quickstart.zh.md b/packages/docs/content/quickstart.zh.md
index 3121597..1dc26cc 100644
--- a/packages/docs/content/quickstart.zh.md
+++ b/packages/docs/content/quickstart.zh.md
@@ -30,7 +30,7 @@ penguin config model add --provider deepseek --model-id deepseek-v4-flash --api-
 penguin web
 ```
 
-服务运行在 http://127.0.0.1:7364 并自动打开浏览器（`--no-open` 跳过）。首次登录使用 `admin` / `penguin-2026`，请立即修改密码。`penguin server` 启动同一进程的 headless 版本。
+服务运行在 http://127.0.0.1:7364 并自动打开浏览器（`--no-open` 跳过）。首次登录使用 `admin`，初始密码（形如 `penguin-1234`）在服务端首次启动时打印，请立即修改密码。`penguin server` 启动同一进程的 headless 版本。
 
 ## 单次运行
 
diff --git a/packages/docs/content/server-api.en.md b/packages/docs/content/server-api.en.md
index f7eef10..7923659 100644
--- a/packages/docs/content/server-api.en.md
+++ b/packages/docs/content/server-api.en.md
@@ -35,12 +35,13 @@ packages/server/src
 
 - Cookie session: `penguin_session` (HttpOnly, SameSite=Lax), valid for 7 days with sliding renewal;
 - Passwords are stored as scrypt hashes; the server keeps only the sha256 of the session token, never the plaintext;
-- No open registration: the built-in admin `admin` / `penguin-2026` is seeded at startup, and all other accounts are created by an admin;
+- No open registration: the built-in admin `admin` is seeded at startup with a random initial password (of the form `penguin-1234`) printed once to the server console — `PENGUIN_SEED_ADMIN_PASSWORD` pins it for automation — and all other accounts are created by an admin;
 - Same-origin only — no CORS middleware is enabled.
 
 ```bash
+# Use the initial password printed at first start (or your changed one).
 curl -c cookies.txt -H "Content-Type: application/json" \
-  -d '{"userId":"admin","password":"penguin-2026"}' \
+  -d '{"userId":"admin","password":"penguin-1234"}' \
   http://127.0.0.1:7364/api/auth/login
 ```
 
diff --git a/packages/docs/content/server-api.zh.md b/packages/docs/content/server-api.zh.md
index f8a0eb3..b97ca3d 100644
--- a/packages/docs/content/server-api.zh.md
+++ b/packages/docs/content/server-api.zh.md
@@ -35,12 +35,13 @@ packages/server/src
 
 - Cookie 会话：`penguin_session`（HttpOnly、SameSite=Lax），有效期 7 天，滑动续期；
 - 密码以 scrypt 哈希存储；服务端只保存会话 Token 的 sha256，不落明文；
-- 不开放注册：启动时种子化内置管理员 `admin` / `penguin-2026`，其余账号由管理员创建；
+- 不开放注册：启动时种子化内置管理员 `admin`，初始密码随机生成（形如 `penguin-1234`）并仅在种子当次打印到服务端控制台——自动化可用 `PENGUIN_SEED_ADMIN_PASSWORD` 固定——其余账号由管理员创建；
 - 仅限同源访问，未启用 CORS 中间件。
 
 ```bash
+# 密码用首次启动时打印的初始密码（或改过之后的密码）。
 curl -c cookies.txt -H "Content-Type: application/json" \
-  -d '{"userId":"admin","password":"penguin-2026"}' \
+  -d '{"userId":"admin","password":"penguin-1234"}' \
   http://127.0.0.1:7364/api/auth/login
 ```
 
diff --git a/packages/docs/content/web-app.en.md b/packages/docs/content/web-app.en.md
index 1a53757..e0cfb73 100644
--- a/packages/docs/content/web-app.en.md
+++ b/packages/docs/content/web-app.en.md
@@ -23,7 +23,7 @@ penguin web
 # open http://127.0.0.1:7364
 ```
 
-The initial account is `admin` / `penguin-2026`. There is no self-registration: accounts are created by an admin on the user-management page, and every new user automatically gets an independent initial Project named `<userId>-default_project`. While the initial password is still in use, a banner prompts the user to change it.
+The initial account is `admin`; its initial password (of the form `penguin-1234`) is printed in the server startup output on first start. There is no self-registration: accounts are created by an admin on the user-management page, and every new user automatically gets an independent initial Project named `<userId>-default_project`. While the initial password is still in use, a banner prompts the user to change it.
 
 Logins persist for 7 days with sliding renewal; an admin password reset invalidates all of that user's login sessions.
 
diff --git a/packages/docs/content/web-app.zh.md b/packages/docs/content/web-app.zh.md
index 4434621..0efd506 100644
--- a/packages/docs/content/web-app.zh.md
+++ b/packages/docs/content/web-app.zh.md
@@ -23,7 +23,7 @@ penguin web
 # 打开 http://127.0.0.1:7364
 ```
 
-初始账号为 `admin` / `penguin-2026`。系统不开放自助注册：账号由管理员在用户管理页创建；每个新用户会自动获得一个独立的初始 Project，命名为 `<userId>-default_project`。仍在使用初始密码时，页面会以横幅提示尽快修改。
+初始账号为 `admin`，初始密码（形如 `penguin-1234`）在服务端首次启动时打印。系统不开放自助注册：账号由管理员在用户管理页创建；每个新用户会自动获得一个独立的初始 Project，命名为 `<userId>-default_project`。仍在使用初始密码时，页面会以横幅提示尽快修改。
 
 登录状态保持 7 天（滑动续期）；管理员重置密码会使该用户的全部登录会话失效。
 
diff --git a/packages/landing/content/blog/easiest-way-to-build-ai-agents-2026.en.md b/packages/landing/content/blog/easiest-way-to-build-ai-agents-2026.en.md
index 6680094..a922811 100644
--- a/packages/landing/content/blog/easiest-way-to-build-ai-agents-2026.en.md
+++ b/packages/landing/content/blog/easiest-way-to-build-ai-agents-2026.en.md
@@ -78,7 +78,7 @@ One install gives you all five rows of that first table, sharing one data direct
 
 ```bash
 curl -fsSL https://penguin.ooo/install.sh | sh
-penguin web        # http://127.0.0.1:7364 — first login: admin / penguin-2026
+penguin web        # http://127.0.0.1:7364 — first login: admin, initial password printed on first start
 ```
 
 Multi-session chat, agent and skill management, model configuration, usage and cost statistics, **Trace observability**, and an **evaluation center** — in the box, wired together, nothing to subscribe to and nothing to self-host separately. Every request, tool call and approval decision is already recorded; a session restores completely from its trace. There is no tracing SDK to install because there is no seam to instrument across.
diff --git a/packages/landing/content/blog/easiest-way-to-build-ai-agents-2026.zh.md b/packages/landing/content/blog/easiest-way-to-build-ai-agents-2026.zh.md
index 639546d..fa058f0 100644
--- a/packages/landing/content/blog/easiest-way-to-build-ai-agents-2026.zh.md
+++ b/packages/landing/content/blog/easiest-way-to-build-ai-agents-2026.zh.md
@@ -72,7 +72,7 @@ LangChain 自己也把遗留的 chain、retriever 和 hub 模块挪进了独立
 
 ```bash
 curl -fsSL https://penguin.ooo/install.sh | sh
-penguin web        # http://127.0.0.1:7364 — 首次登录：admin / penguin-2026
+penguin web        # http://127.0.0.1:7364 — 首次登录：admin，初始密码见首次启动输出
 ```
 
 多会话对话、Agent 与技能管理、模型配置、用量与成本统计、**Trace 可观测**、**评测中心**，开箱即有，彼此已经打通，**不用订阅什么，也不用另外自建什么**。每个请求、每次工具调用、每个审批决策都已经记下来了，会话可以从 Trace 完整恢复。**这里没有追踪 SDK 要接，因为根本不存在需要跨越的接缝。**
diff --git a/packages/landing/content/blog/fireworks-credits-amd.en.md b/packages/landing/content/blog/fireworks-credits-amd.en.md
index 7e25153..f8732f2 100644
--- a/packages/landing/content/blog/fireworks-credits-amd.en.md
+++ b/packages/landing/content/blog/fireworks-credits-amd.en.md
@@ -65,7 +65,7 @@ With the API key in hand, three steps:
 
 ```bash
 curl -fsSL https://penguin.ooo/install.sh | sh
-penguin web        # opens http://127.0.0.1:7364 (first login: admin / penguin-2026)
+penguin web        # opens http://127.0.0.1:7364 (first login: admin, initial password printed on first start)
 ```
 
 **2. Configure a Fireworks model**
diff --git a/packages/landing/content/blog/fireworks-credits-amd.zh.md b/packages/landing/content/blog/fireworks-credits-amd.zh.md
index d62e454..80214cd 100644
--- a/packages/landing/content/blog/fireworks-credits-amd.zh.md
+++ b/packages/landing/content/blog/fireworks-credits-amd.zh.md
@@ -65,7 +65,7 @@ AMD 会验证账户与申请资料，通常需要 **2–3 个工作日**；实
 
 ```bash
 curl -fsSL https://penguin.ooo/install.sh | sh
-penguin web        # 打开 http://127.0.0.1:7364（首次登录：admin / penguin-2026）
+penguin web        # 打开 http://127.0.0.1:7364（首次登录：admin，初始密码见首次启动输出）
 ```
 
 **2. 配置 Fireworks 模型**
diff --git a/packages/landing/content/blog/introducing-penguinharness.en.md b/packages/landing/content/blog/introducing-penguinharness.en.md
index 26f2f55..da6acb4 100644
--- a/packages/landing/content/blog/introducing-penguinharness.en.md
+++ b/packages/landing/content/blog/introducing-penguinharness.en.md
@@ -92,7 +92,7 @@ Install with one command (Linux / macOS, x64 / arm64, bundled Node runtime), the
 
 ```bash
 curl -fsSL https://penguin.ooo/install.sh | sh
-penguin web        # opens http://127.0.0.1:7364 (first login: admin / penguin-2026)
+penguin web        # opens http://127.0.0.1:7364 (first login: admin, initial password printed on first start)
 ```
 
 Open the Models page, paste an API key under the DeepSeek or OpenRouter group and set it as default; then head back to Chat and hand the Agent its first task — e.g. "Analyze data.csv and summarize quarterly sales".
diff --git a/packages/landing/content/blog/introducing-penguinharness.zh.md b/packages/landing/content/blog/introducing-penguinharness.zh.md
index aa476fd..edf27d5 100644
--- a/packages/landing/content/blog/introducing-penguinharness.zh.md
+++ b/packages/landing/content/blog/introducing-penguinharness.zh.md
@@ -92,7 +92,7 @@ Token 与成本均为全套题目合计，不是单次均值。数据分析套
 
 ```bash
 curl -fsSL https://penguin.ooo/install.sh | sh
-penguin web        # 打开 http://127.0.0.1:7364（首次登录：admin / penguin-2026）
+penguin web        # 打开 http://127.0.0.1:7364（首次登录：admin，初始密码见首次启动输出）
 ```
 
 进入「模型仓库」页，在 DeepSeek 或 OpenRouter 分组里粘贴 API key 并设为默认；回到对话页，把第一个任务交给 Agent——例如「分析 data.csv，输出各季度销售额汇总」。
diff --git a/packages/landing/scripts/capture-blog-013-shots.mjs b/packages/landing/scripts/capture-blog-013-shots.mjs
index f055ff0..f0b6529 100644
--- a/packages/landing/scripts/capture-blog-013-shots.mjs
+++ b/packages/landing/scripts/capture-blog-013-shots.mjs
@@ -45,6 +45,8 @@ const ROOT = path.resolve(HERE, "../../..");
 const OUT_DIR = path.resolve(HERE, "../.blog-assets");
 const MOCK_PORT = 8953; // Distinct from capture-shots (8940/8941) and blog-shots (8944).
 const SRV_PORT = 8952;
+// Pins the otherwise-random seeded admin password (PENGUIN_SEED_ADMIN_PASSWORD below).
+const ADMIN_PASSWORD = "penguin-0000";
 // The App is canonically served on `localhost` (127.0.0.1 is the Workspace-preview host).
 const BASE = `http://localhost:${SRV_PORT}`;
 const MOCK = `http://127.0.0.1:${MOCK_PORT}`;
@@ -932,6 +934,7 @@ const srv = spawn("node", [path.join(ROOT, "packages/server/dist/index.js")], {
     PENGUIN_WEB_DIST: path.join(ROOT, "packages/web/dist"),
     PORT: String(SRV_PORT),
     HOST: "127.0.0.1",
+    PENGUIN_SEED_ADMIN_PASSWORD: ADMIN_PASSWORD,
   },
   stdio: ["ignore", "pipe", "pipe"],
 });
@@ -950,7 +953,7 @@ try {
   await waitFor(`${BASE}/`);
   console.log(`[blog-013] server ready on ${BASE}`);
 
-  const adminCookie = await login("admin", "penguin-2026");
+  const adminCookie = await login("admin", ADMIN_PASSWORD);
   const browser = await chromium.launch();
 
   // WebP encoder: Chromium re-encodes the PNG screenshot via canvas (capture-shots convention).
diff --git a/packages/landing/scripts/capture-blog-shots.mjs b/packages/landing/scripts/capture-blog-shots.mjs
index 0895f31..ebf8cff 100644
--- a/packages/landing/scripts/capture-blog-shots.mjs
+++ b/packages/landing/scripts/capture-blog-shots.mjs
@@ -36,6 +36,8 @@ const ROOT = path.resolve(HERE, "../../..");
 // Gitignored staging dir: these images are hosted in the community repo, not committed here.
 const OUT_DIR = path.resolve(HERE, "../.blog-assets");
 const SRV_PORT = 8944; // Distinct from capture-shots.mjs (8940/8941) so both can run.
+// Pins the otherwise-random seeded admin password (PENGUIN_SEED_ADMIN_PASSWORD below).
+const ADMIN_PASSWORD = "penguin-0000";
 // On loopback binds the App is canonically served on `localhost`; the 127.0.0.1
 // counterpart is the Workspace-preview host, where /api deliberately answers 401
 // (see server app.ts's canonical-host guard).
@@ -113,6 +115,7 @@ const srv = spawn("node", [path.join(ROOT, "packages/server/dist/index.js")], {
     PENGUIN_WEB_DIST: path.join(ROOT, "packages/web/dist"),
     PORT: String(SRV_PORT),
     HOST: "127.0.0.1",
+    PENGUIN_SEED_ADMIN_PASSWORD: ADMIN_PASSWORD,
   },
   stdio: ["ignore", "pipe", "pipe"],
 });
@@ -127,7 +130,7 @@ try {
   await waitFor(`${BASE}/`);
   console.log(`[blog-shots] server ready on ${BASE}`);
 
-  const adminCookie = await login("admin", "penguin-2026");
+  const adminCookie = await login("admin", ADMIN_PASSWORD);
   const browser = await chromium.launch();
 
   // WebP encoder: Chromium re-encodes the PNG screenshot buffer via canvas (same
diff --git a/packages/landing/scripts/capture-shots.mjs b/packages/landing/scripts/capture-shots.mjs
index 314a8fe..7af362b 100644
--- a/packages/landing/scripts/capture-shots.mjs
+++ b/packages/landing/scripts/capture-shots.mjs
@@ -27,6 +27,8 @@ const OUT_DIR = path.resolve(HERE, "../src/assets/shots");
 const MOCK_PORT = 8941;
 const SRV_PORT = 8940;
 const BASE = `http://127.0.0.1:${SRV_PORT}`;
+// Pins the otherwise-random seeded admin password (PENGUIN_SEED_ADMIN_PASSWORD below).
+const ADMIN_PASSWORD = "penguin-0000";
 const MOCK = `http://127.0.0.1:${MOCK_PORT}`;
 
 // ---------------------------------------------------------------------------
@@ -523,6 +525,7 @@ const srv = spawn("node", [path.join(ROOT, "packages/server/dist/index.js")], {
     PENGUIN_WEB_DIST: path.join(ROOT, "packages/web/dist"),
     PORT: String(SRV_PORT),
     HOST: "127.0.0.1",
+    PENGUIN_SEED_ADMIN_PASSWORD: ADMIN_PASSWORD,
   },
   stdio: ["ignore", "pipe", "pipe"],
 });
@@ -542,7 +545,7 @@ try {
   await waitFor(`${BASE}/`);
   console.log(`[shots] server ready on ${BASE}`);
 
-  const admin = await login("admin", "penguin-2026");
+  const admin = await login("admin", ADMIN_PASSWORD);
   const browser = await chromium.launch();
 
   // WebP encoder: Chromium re-encodes the PNG screenshot buffer via canvas, which
diff --git a/packages/landing/src/lib/strings-en.ts b/packages/landing/src/lib/strings-en.ts
index fefdf84..974bfd4 100644
--- a/packages/landing/src/lib/strings-en.ts
+++ b/packages/landing/src/lib/strings-en.ts
@@ -172,7 +172,7 @@ export const en: Strings = {
     tabCli: "CLI",
     webStep2: "Open the web interface",
     webStep2Desc:
-      "penguin web starts the local service and opens your browser; sign in with the built-in admin account admin / penguin-2026 (change the password right after).",
+      "penguin web starts the local service and opens your browser; sign in as the built-in admin “admin” with the initial password printed in the terminal on first start (looks like penguin-1234; change it right after).",
     webCmd: "penguin web   # opens http://127.0.0.1:7364",
     webStep3: "Configure a model in the UI and start chatting",
     webStep3Desc:
diff --git a/packages/landing/src/lib/strings.ts b/packages/landing/src/lib/strings.ts
index 55acb71..5e5e975 100644
--- a/packages/landing/src/lib/strings.ts
+++ b/packages/landing/src/lib/strings.ts
@@ -176,7 +176,7 @@ export const zh = {
     tabCli: "命令行",
     webStep2: "启动 Web 界面",
     webStep2Desc:
-      "penguin web 启动本地服务并打开浏览器，用内置管理员 admin / penguin-2026 登录（登录后请尽快修改密码）。",
+      "penguin web 启动本地服务并打开浏览器，用内置管理员 admin 登录——初始密码在服务端首次启动时打印到终端（形如 penguin-1234），登录后请尽快修改密码。",
     webCmd: "penguin web   # 打开 http://127.0.0.1:7364",
     webStep3: "在界面里配置模型，开始对话",
     webStep3Desc:
diff --git a/packages/server/README.md b/packages/server/README.md
index 8095060..8e0737e 100644
--- a/packages/server/README.md
+++ b/packages/server/README.md
@@ -36,8 +36,8 @@ pnpm --filter @prismshadow/penguin-server start   # node dist/index.js
 ## Security notes (known MVP limits)
 
 - **CSRF**: session cookie is `SameSite=Lax` and writes accept only `Content-Type: application/json`; no CSRF token yet.
-- **No login rate limiting**: add throttling at a reverse proxy for public deployments.
-- **Built-in admin starts as `admin` / `penguin-2026`**: change it immediately (a banner keeps reminding until you do).
+- **Login throttling**: per-username exponential backoff after 5 consecutive failures (1s doubling to a 60s cap, `429 too_many_attempts` inside the window, reset on success; in-memory, so a restart clears it). Unknown usernames are throttled identically, so it is not an account-existence oracle. A reverse proxy can still add IP-level limits for public deployments.
+- **Built-in admin `admin` starts with a random initial password** of the form `penguin-1234`, printed once to the server console at seed time (`PENGUIN_SEED_ADMIN_PASSWORD` pins it for tests/e2e): change it immediately (a banner keeps reminding until you do).
 - Passwords use `node:crypto` scrypt (`scrypt$N$r$p$salt$hash`, timingSafeEqual); login sessions renew on a 7-day sliding window; the DB stores only the token's sha256.
 - Model credentials live in the Project's hidden 0600 config file; the API always masks them.
 - Behind a reverse proxy, disable response buffering for SSE paths (the server already sends `X-Accel-Buffering: no`) and forward `x-forwarded-proto` to enable Secure cookies.
diff --git a/packages/server/src/app.ts b/packages/server/src/app.ts
index 1745886..89b8135 100644
--- a/packages/server/src/app.ts
+++ b/packages/server/src/app.ts
@@ -214,6 +214,7 @@ export function buildAppDeps(config: ServerConfig, overrides: BuildDepsOverrides
     authSessions: authSessionsRepo,
     provisionInitialProject: (user, isAdmin) =>
       projectService.provisionInitialProject(user, isAdmin),
+    seedAdminPassword: config.seedAdminPassword,
     sessionTtlMs: config.authSessionTtlMs,
     sessionRenewMs: config.authSessionRenewMs,
     ...(overrides.now ? { now: overrides.now } : {}),
diff --git a/packages/server/src/auth/service.ts b/packages/server/src/auth/service.ts
index d1ba279..6f91779 100644
--- a/packages/server/src/auth/service.ts
+++ b/packages/server/src/auth/service.ts
@@ -3,15 +3,16 @@
  * login / logout / password change / session validation.
  *
  * - No open registration: on startup, if there are no users at all, the built-in
- *   admin `admin` is seeded (initial password penguin-2026), and it adopts
- *   `default_project`; all other users are created by an admin via the user
- *   backend (admin-service).
+ *   admin `admin` is seeded with a random `penguin-<4 digits>` initial password
+ *   (printed once by the startup entrypoint; PENGUIN_SEED_ADMIN_PASSWORD injects
+ *   a fixed one for tests/e2e), and it adopts `default_project`; all other users
+ *   are created by an admin via the user backend (admin-service).
  * - An initial password (whether seeded or set by an admin) is flagged with
  *   password_is_initial, which the frontend uses to prompt for a password change soon.
  * - Sessions: a 32-byte random token, with only its sha256 hash stored in the DB;
  *   valid for 7 days, with sliding renewal once less than 6 days remain.
  */
-import { createHash, randomBytes } from "node:crypto";
+import { createHash, randomBytes, randomInt } from "node:crypto";
 import type { UserInfo } from "../api/types.js";
 import { HttpError } from "../http/errors.js";
 import type { AuthSessionsRepo } from "../db/repos/auth-sessions.js";
@@ -20,9 +21,37 @@ import { hashPassword, verifyPassword } from "./password.js";
 
 export const MIN_PASSWORD_LENGTH = 8;
 
-/** Built-in admin: user_id and initial password (matches the README and login-page hint). */
+/** Built-in admin user_id. */
 export const ADMIN_USER_ID = "admin";
-export const ADMIN_INITIAL_PASSWORD = "penguin-2026";
+
+/**
+ * Login throttling (per userId): the seeded initial password is `penguin-<4 digits>` —
+ * 10,000 combinations — so unthrottled guessing would enumerate it in minutes. After
+ * LOGIN_FREE_ATTEMPTS consecutive failures, the next attempt is admitted only after an
+ * exponentially growing delay from the last failure (1s, 2s, … capped at 60s; attempts
+ * inside the window are 429 `too_many_attempts` and do not extend it). Beyond ~40
+ * failures that is one guess per minute, so the 10k space stops being enumerable, while
+ * a legitimate user who mistyped a few times never waits more than the cap. A successful
+ * login clears the counter. Counters are process memory (a restart clears them —
+ * restarting is slower than waiting out the cap) and are kept for nonexistent userIds
+ * too, so throttling is not an account-existence oracle. Known limit: a concurrent burst
+ * can slip in before its first failure is recorded; the steady-state backoff still
+ * dominates the search space.
+ */
+const LOGIN_FREE_ATTEMPTS = 5;
+const LOGIN_BACKOFF_START_MS = 1000;
+const LOGIN_BACKOFF_CAP_MS = 60_000;
+/** Failure entries idle longer than this are swept (bounds the map; far above the cap). */
+const LOGIN_FAILURE_IDLE_MS = 15 * 60_000;
+
+/**
+ * Random initial password for the seeded admin: `penguin-<4 digits>` — brand-related and
+ * easy to type, shown once in the server startup output (the README, docs and login-page
+ * hint all describe this form).
+ */
+export function generateInitialAdminPassword(): string {
+  return "penguin-" + String(randomInt(0, 10000)).padStart(4, "0");
+}
 
 function sha256Hex(value: string): string {
   return createHash("sha256").update(value).digest("hex");
@@ -42,6 +71,8 @@ export interface AuthServiceDeps {
   authSessions: AuthSessionsRepo;
   /** Provisions the initial Project at signup (injected by project-service, to avoid a circular dependency). */
   provisionInitialProject: (user: UserRow, isAdmin: boolean) => Promise<void>;
+  /** Fixed initial password for the seeded admin (config.seedAdminPassword); null generates a random one at seed time. */
+  seedAdminPassword: string | null;
   sessionTtlMs: number;
   sessionRenewMs: number;
   now?: () => Date;
@@ -58,12 +89,25 @@ export class AuthService {
    * Startup seeding (idempotent): creates the built-in admin and adopts
    * default_project when the users table is empty; if the initial Project fails,
    * the user row is rolled back and the server retries on next startup.
+   * Returns the initial password when it actually seeded — the caller prints it,
+   * the only place a generated password is ever shown — and null when users
+   * already exist.
    */
-  async seedAdmin(): Promise<void> {
-    if (this.deps.users.count() > 0) return;
+  async seedAdmin(): Promise<string | null> {
+    if (this.deps.users.count() > 0) return null;
+    const password = this.deps.seedAdminPassword ?? generateInitialAdminPassword();
+    // The override (PENGUIN_SEED_ADMIN_PASSWORD) must meet the same policy as every
+    // other initial/reset password; rejecting it here, before any insert, keeps a
+    // configuration typo from creating a trivially weak privileged account. Generated
+    // passwords are always 12 characters and never trip this.
+    if (password.length < MIN_PASSWORD_LENGTH) {
+      throw new Error(
+        `PENGUIN_SEED_ADMIN_PASSWORD must be at least ${MIN_PASSWORD_LENGTH} characters.`,
+      );
+    }
     const user: UserRow = {
       userId: ADMIN_USER_ID,
-      passwordHash: await hashPassword(ADMIN_INITIAL_PASSWORD),
+      passwordHash: await hashPassword(password),
       isAdmin: true,
       passwordIsInitial: true,
       createdAt: this.now().toISOString(),
@@ -75,14 +119,45 @@ export class AuthService {
       this.deps.users.delete(user.userId);
       throw err;
     }
+    return password;
+  }
+
+  /** Consecutive login failures per userId (see the throttling comment on the constants). */
+  private readonly loginFailures = new Map<string, { failures: number; lastFailureAt: number }>();
+
+  /** The wait imposed after `failures` consecutive failures (0 while within the free attempts). */
+  private loginDelayMs(failures: number): number {
+    const excess = failures - LOGIN_FREE_ATTEMPTS;
+    if (excess <= 0) return 0;
+    return Math.min(LOGIN_BACKOFF_START_MS * 2 ** (excess - 1), LOGIN_BACKOFF_CAP_MS);
   }
 
   async login(userId: string, password: string): Promise<{ user: UserInfo; token: string }> {
+    const nowMs = this.now().getTime();
+    for (const [key, entry] of this.loginFailures) {
+      if (nowMs - entry.lastFailureAt > LOGIN_FAILURE_IDLE_MS) this.loginFailures.delete(key);
+    }
+    const failed = this.loginFailures.get(userId);
+    if (failed) {
+      const readyAt = failed.lastFailureAt + this.loginDelayMs(failed.failures);
+      if (nowMs < readyAt) {
+        throw new HttpError(
+          429,
+          "too_many_attempts",
+          `Too many failed sign-in attempts. Try again in ${Math.ceil((readyAt - nowMs) / 1000)}s.`,
+        );
+      }
+    }
     const row = this.deps.users.findById(userId);
     const ok = row !== null && (await verifyPassword(password, row.passwordHash));
     if (!row || !ok) {
+      this.loginFailures.set(userId, {
+        failures: (failed?.failures ?? 0) + 1,
+        lastFailureAt: this.now().getTime(),
+      });
       throw new HttpError(401, "invalid_credentials", "Incorrect username or password.");
     }
+    this.loginFailures.delete(userId);
     this.deps.authSessions.deleteExpired(this.now().toISOString());
     return { user: toUserInfo(row), token: this.issueSession(row.userId) };
   }
diff --git a/packages/server/src/config.ts b/packages/server/src/config.ts
index 44b14bc..6219fe2 100644
--- a/packages/server/src/config.ts
+++ b/packages/server/src/config.ts
@@ -32,6 +32,12 @@ export interface ServerConfig {
    * derived per request instead. See design § "Workspace 文件预览".
    */
   previewOrigin: string | null;
+  /**
+   * Fixed initial password for the seeded built-in admin (PENGUIN_SEED_ADMIN_PASSWORD),
+   * used by automated tests and e2e; null (the norm) makes the seed generate a random
+   * `penguin-<4 digits>` password, printed once to the server console.
+   */
+  seedAdminPassword: string | null;
   /** Login session validity period (7 days). */
   authSessionTtlMs: number;
   /** Sliding renewal threshold: if the remaining validity is below this value when validation succeeds, it's renewed to the full TTL (renews under 6 days). */
@@ -73,7 +79,7 @@ function normalizePreviewOrigin(raw: string | undefined): string | null {
   return url.origin;
 }
 
-/** Parses server config from environment variables (PORT / HOST / PENGUIN_HOME / PENGUIN_WEB_DIST / PENGUIN_WEB_DB / PENGUIN_PREVIEW_ORIGIN). */
+/** Parses server config from environment variables (PORT / HOST / PENGUIN_HOME / PENGUIN_WEB_DIST / PENGUIN_WEB_DB / PENGUIN_PREVIEW_ORIGIN / PENGUIN_SEED_ADMIN_PASSWORD). */
 export function resolveServerConfig(env: NodeJS.ProcessEnv = process.env): ServerConfig {
   const root = env.PENGUIN_HOME ?? resolveRoot();
   // An empty PORT string is treated as unset (the common `.env` case of an empty
@@ -90,6 +96,8 @@ export function resolveServerConfig(env: NodeJS.ProcessEnv = process.env): Serve
     dbPath: env.PENGUIN_WEB_DB ?? path.join(root, "web.db"),
     webDist: env.PENGUIN_WEB_DIST ?? defaultWebDist(),
     previewOrigin: normalizePreviewOrigin(env.PENGUIN_PREVIEW_ORIGIN),
+    // An empty/whitespace value is treated as unset (→ random seed password).
+    seedAdminPassword: env.PENGUIN_SEED_ADMIN_PASSWORD?.trim() || null,
     authSessionTtlMs: 7 * DAY_MS,
     authSessionRenewMs: 6 * DAY_MS,
   };
diff --git a/packages/server/src/index.ts b/packages/server/src/index.ts
index f61f5e6..9f3a9f9 100644
--- a/packages/server/src/index.ts
+++ b/packages/server/src/index.ts
@@ -21,8 +21,15 @@ const config = resolveServerConfig();
 const deps = buildAppDeps(config);
 const app = createApp(deps);
 
-// Built-in admin seed (idempotent): creates admin (initial password penguin-2026) and adopts default_project when the users table is empty.
-await deps.authService.seedAdmin();
+// Built-in admin seed (idempotent): creates admin and adopts default_project when the
+// users table is empty. The returned initial password (random unless pinned via
+// PENGUIN_SEED_ADMIN_PASSWORD) is printed here once — the only place it is ever shown.
+const seededAdminPassword = await deps.authService.seedAdmin();
+if (seededAdminPassword !== null) {
+  console.log(
+    `Seeded built-in admin "admin" — initial password: ${seededAdminPassword} (change it after first sign-in)`,
+  );
+}
 
 // Schedule scheduler: startup reconciliation (missed, don't backfill) + periodic scan; only active while the server is running.
 await deps.scheduler.start();
diff --git a/packages/server/test/auth.test.ts b/packages/server/test/auth.test.ts
index 38063b0..efca8d9 100644
--- a/packages/server/test/auth.test.ts
+++ b/packages/server/test/auth.test.ts
@@ -6,7 +6,18 @@ import fs from "node:fs/promises";
 import path from "node:path";
 import { afterEach, beforeEach, describe, expect, it } from "vitest";
 import type { MeResponse, ProjectsResponse } from "../src/api/types.js";
-import { apiClient, createTestApp, loginAdmin, loginUser, provisionUser } from "./helpers.js";
+import { buildAppDeps } from "../src/app.js";
+import { generateInitialAdminPassword } from "../src/auth/service.js";
+import {
+  apiClient,
+  createTestApp,
+  loginAdmin,
+  loginUser,
+  makeTempRoot,
+  provisionUser,
+  TEST_ADMIN_PASSWORD,
+  testConfig,
+} from "./helpers.js";
 import type { TestApp } from "./helpers.js";
 
 describe("auth", () => {
@@ -55,8 +66,8 @@ describe("auth", () => {
     await expect(
       fs.access(path.join(t.root, "default_project", "agents", "default_agent", "agent_state")),
     ).resolves.toBeUndefined();
-    // Seeding is idempotent: re-seeding does not create a duplicate account.
-    await t.deps.authService.seedAdmin();
+    // Seeding is idempotent: re-seeding returns null and does not create a duplicate account.
+    expect(await t.deps.authService.seedAdmin()).toBeNull();
     expect(t.deps.db.prepare("SELECT COUNT(*) AS n FROM users").get()?.n).toBe(1);
   });
 
@@ -159,6 +170,98 @@ describe("auth", () => {
     expect(got.prefs.theme).toBe("dark");
   });
 
+  it("seedAdmin without an injected password generates penguin-<4 digits> and returns it", async () => {
+    // Bypass the fixed test password: null matches the production default (random generation).
+    const fresh = await createTestApp({ config: { seedAdminPassword: null } });
+    try {
+      expect(fresh.adminPassword).toMatch(/^penguin-\d{4}$/);
+      // The returned password is the one that actually logs in.
+      await loginUser(fresh.app, "admin", fresh.adminPassword);
+      // Users exist now: re-seeding reports that nothing was seeded.
+      expect(await fresh.deps.authService.seedAdmin()).toBeNull();
+    } finally {
+      await fresh.cleanup();
+    }
+  });
+
+  it("seedAdmin honors the injected seedAdminPassword", async () => {
+    const fresh = await createTestApp({ config: { seedAdminPassword: "penguin-7777" } });
+    try {
+      expect(fresh.adminPassword).toBe("penguin-7777");
+      await loginUser(fresh.app, "admin", "penguin-7777");
+    } finally {
+      await fresh.cleanup();
+    }
+  });
+
+  it("seedAdmin rejects an override below the password policy before creating the account", async () => {
+    const root = await makeTempRoot();
+    const deps = buildAppDeps({ ...testConfig(root), seedAdminPassword: "x" }, { log: () => {} });
+    try {
+      await expect(deps.authService.seedAdmin()).rejects.toThrow(/at least 8 characters/);
+      // Rejected before any insert: no half-created privileged account to retry around.
+      expect(deps.db.prepare("SELECT COUNT(*) AS n FROM users").get()?.n).toBe(0);
+    } finally {
+      deps.channels.dispose();
+      deps.db.close();
+      await fs.rm(root, { recursive: true, force: true, maxRetries: 10, retryDelay: 100 });
+    }
+  });
+
+  it("throttles login failures per username with exponential backoff and resets on success", async () => {
+    let clock = Date.parse("2026-08-03T00:00:00Z");
+    const fresh = await createTestApp({ now: () => new Date(clock) });
+    try {
+      const attempt = (password: string) =>
+        fresh.app.request("/api/auth/login", {
+          method: "POST",
+          headers: { "content-type": "application/json" },
+          body: JSON.stringify({ userId: "admin", password }),
+        });
+      // Five free failures, and the sixth still reaches verification (backoff starts after it).
+      for (let i = 0; i < 6; i++) expect((await attempt("wrong-password")).status).toBe(401);
+      // Inside the 1s window: rejected without touching credentials — even the CORRECT password.
+      const throttled = await attempt("wrong-password");
+      expect(throttled.status).toBe(429);
+      const body = (await throttled.json()) as { error: { code: string } };
+      expect(body.error.code).toBe("too_many_attempts");
+      expect((await attempt(TEST_ADMIN_PASSWORD)).status).toBe(429);
+      // Past the window, the correct password signs in and clears the counter…
+      clock += 1100;
+      await loginUser(fresh.app, "admin", TEST_ADMIN_PASSWORD);
+      // …so the next failure is an ordinary 401 again, not a 429.
+      expect((await attempt("wrong-password")).status).toBe(401);
+    } finally {
+      await fresh.cleanup();
+    }
+  });
+
+  it("throttles unknown usernames identically (no account-existence oracle)", async () => {
+    let clock = Date.parse("2026-08-03T00:00:00Z");
+    const fresh = await createTestApp({ now: () => new Date(clock) });
+    try {
+      const attempt = () =>
+        fresh.app.request("/api/auth/login", {
+          method: "POST",
+          headers: { "content-type": "application/json" },
+          body: JSON.stringify({ userId: "ghost", password: "whatever-123" }),
+        });
+      for (let i = 0; i < 6; i++) expect((await attempt()).status).toBe(401);
+      expect((await attempt()).status).toBe(429);
+      // The window expires on the same schedule as for real accounts.
+      clock += 1100;
+      expect((await attempt()).status).toBe(401);
+    } finally {
+      await fresh.cleanup();
+    }
+  });
+
+  it("generateInitialAdminPassword matches penguin-<4 digits>", () => {
+    for (let i = 0; i < 32; i++) {
+      expect(generateInitialAdminPassword()).toMatch(/^penguin-\d{4}$/);
+    }
+  });
+
   it("PUT prefs shallow-merges without clobbering other writers' fields", async () => {
     const { cookie } = await provisionUser(t.app, "fred");
     const api = apiClient(t.app, cookie);
diff --git a/packages/server/test/config.test.ts b/packages/server/test/config.test.ts
index 9479c00..b7eb8a1 100644
--- a/packages/server/test/config.test.ts
+++ b/packages/server/test/config.test.ts
@@ -1,9 +1,12 @@
 /**
- * resolveServerConfig PORT parsing tests: both the default (missing) and empty string
- * (the common `PORT=` empty value in `.env`) fall back to 7364 — Number("") === 0 used
- * to make the empty string pass range validation and bind to a random port; explicit
- * "0" is preserved (explicit semantics for a random available port); invalid values
- * throw. This matches the CLI's resolvePort semantics (packages/cli serve).
+ * resolveServerConfig parsing tests.
+ *
+ * PORT: both the default (missing) and empty string (the common `PORT=` empty value in
+ * `.env`) fall back to 7364 — Number("") === 0 used to make the empty string pass range
+ * validation and bind to a random port; explicit "0" is preserved (explicit semantics
+ * for a random available port); invalid values throw. This matches the CLI's
+ * resolvePort semantics (packages/cli serve).
+ * PENGUIN_SEED_ADMIN_PASSWORD: unset/empty/whitespace → null (random seed password).
  */
 import { describe, expect, it } from "vitest";
 import { resolveServerConfig } from "../src/config.js";
@@ -27,3 +30,19 @@ describe("resolveServerConfig: PORT parsing", () => {
     }
   });
 });
+
+describe("resolveServerConfig: PENGUIN_SEED_ADMIN_PASSWORD parsing", () => {
+  it("unset/empty/whitespace → null; a value is kept trimmed", () => {
+    expect(resolveServerConfig({ ...base }).seedAdminPassword).toBeNull();
+    expect(
+      resolveServerConfig({ ...base, PENGUIN_SEED_ADMIN_PASSWORD: "" }).seedAdminPassword,
+    ).toBeNull();
+    expect(
+      resolveServerConfig({ ...base, PENGUIN_SEED_ADMIN_PASSWORD: "  " }).seedAdminPassword,
+    ).toBeNull();
+    expect(
+      resolveServerConfig({ ...base, PENGUIN_SEED_ADMIN_PASSWORD: " penguin-9999 " })
+        .seedAdminPassword,
+    ).toBe("penguin-9999");
+  });
+});
diff --git a/packages/server/test/helpers.ts b/packages/server/test/helpers.ts
index b8b9b2a..69e1a88 100644
--- a/packages/server/test/helpers.ts
+++ b/packages/server/test/helpers.ts
@@ -11,7 +11,7 @@ import type { OmniMessage } from "@prismshadow/penguin-core";
 import { buildAppDeps, createApp } from "../src/app.js";
 import type { AppDeps, BuildDepsOverrides } from "../src/app.js";
 import type { AppEnv } from "../src/auth/middleware.js";
-import { ADMIN_INITIAL_PASSWORD, ADMIN_USER_ID } from "../src/auth/service.js";
+import { ADMIN_USER_ID } from "../src/auth/service.js";
 import type { ServerConfig } from "../src/config.js";
 import type { UserInfo } from "../src/api/types.js";
 
@@ -21,6 +21,9 @@ export async function makeTempRoot(): Promise<string> {
 
 const DAY_MS = 24 * 60 * 60 * 1000;
 
+/** Fixed seeded-admin password injected into every test app (in production the seed generates a random one). */
+export const TEST_ADMIN_PASSWORD = "penguin-0000";
+
 export function testConfig(root: string): ServerConfig {
   return {
     root,
@@ -32,6 +35,8 @@ export function testConfig(root: string): ServerConfig {
     previewOrigin: null,
     // Points to a nonexistent directory: static hosting is disabled in tests.
     webDist: path.join(root, "__no_web_dist__"),
+    // Fixed seed password so loginAdmin needs no seed-time capture.
+    seedAdminPassword: TEST_ADMIN_PASSWORD,
     authSessionTtlMs: 7 * DAY_MS,
     authSessionRenewMs: 6 * DAY_MS,
   };
@@ -41,6 +46,8 @@ export interface TestApp {
   app: Hono<AppEnv>;
   deps: AppDeps;
   root: string;
+  /** Initial password of the seeded admin (TEST_ADMIN_PASSWORD unless overridden via `config.seedAdminPassword`). */
+  adminPassword: string;
   cleanup(): Promise<void>;
 }
 
@@ -56,13 +63,15 @@ export async function createTestApp(options: TestAppOptions = {}): Promise<TestA
   const root = await makeTempRoot();
   if (beforeSeed) await beforeSeed(root);
   const deps = buildAppDeps({ ...testConfig(root), ...config }, { log: () => {}, ...overrides });
-  // Consistent with the startup entrypoint: seed the built-in admin (owning default_project).
-  await deps.authService.seedAdmin();
+  // Consistent with the startup entrypoint: seed the built-in admin (owning default_project),
+  // keeping the password it returns (only null if a beforeSeed hook ever pre-created users).
+  const adminPassword = (await deps.authService.seedAdmin()) ?? TEST_ADMIN_PASSWORD;
   const app = createApp(deps);
   return {
     app,
     deps,
     root,
+    adminPassword,
     cleanup: async () => {
       deps.channels.dispose();
       deps.db.close();
@@ -95,9 +104,9 @@ export async function loginUser(
   return { cookie: setCookie.split(";")[0]!, user: body.user };
 }
 
-/** Logs in as the seeded admin. */
+/** Logs in as the seeded admin (every test app seeds with TEST_ADMIN_PASSWORD). */
 export function loginAdmin(app: Hono<AppEnv>): Promise<{ cookie: string; user: UserInfo }> {
-  return loginUser(app, ADMIN_USER_ID, ADMIN_INITIAL_PASSWORD);
+  return loginUser(app, ADMIN_USER_ID, TEST_ADMIN_PASSWORD);
 }
 
 /** Admin creates the account and logs in as that user (the only way to create test users while registration is closed). */
diff --git a/packages/web/e2e/auth.mjs b/packages/web/e2e/auth.mjs
index 4d471a5..9f4adbb 100644
--- a/packages/web/e2e/auth.mjs
+++ b/packages/web/e2e/auth.mjs
@@ -1,9 +1,11 @@
 /**
  * e2e auth helper: with signup disabled, test users are always provisioned via
- * the built-in admin account, then logged in. The server seeds an admin
- * (admin / penguin-2026) on startup; a single e2e run shares one data root, and
- * provisioning is idempotent (reuses the user if it already exists) so a
- * single spec can be rerun on its own.
+ * the built-in admin account, then logged in. The seeded admin password is
+ * random in production; run.sh starts the e2e server with
+ * PENGUIN_SEED_ADMIN_PASSWORD=penguin-2026 to pin it to the constant below.
+ * A single e2e run shares one data root, and provisioning is idempotent
+ * (reuses the user if it already exists) so a single spec can be rerun on its
+ * own.
  */
 import { request } from "@playwright/test";
 
diff --git a/packages/web/e2e/run.sh b/packages/web/e2e/run.sh
index eeafa69..d09c875 100644
--- a/packages/web/e2e/run.sh
+++ b/packages/web/e2e/run.sh
@@ -32,8 +32,11 @@ MOCK_PORT=$MOCK_PORT node "$HERE/mock-llm.mjs" &
 MOCK_PID=$!
 
 echo "== start server =="
+# PENGUIN_SEED_ADMIN_PASSWORD pins the otherwise-random seeded admin password to the
+# constant the specs use (ADMIN_PASSWORD in auth.mjs).
 PENGUIN_HOME="$DATA" PORT=$SRV_PORT HOST=127.0.0.1 PENGUIN_WEB_DB="$DATA/web.db" \
   PENGUIN_WEB_DIST="$ROOT/packages/web/dist" \
+  PENGUIN_SEED_ADMIN_PASSWORD=penguin-2026 \
   node "$ROOT/packages/server/dist/index.js" &
 SRV_PID=$!
 
diff --git a/packages/web/src/lib/strings-en.ts b/packages/web/src/lib/strings-en.ts
index da862ae..f1df81c 100644
--- a/packages/web/src/lib/strings-en.ts
+++ b/packages/web/src/lib/strings-en.ts
@@ -130,13 +130,14 @@ export const en: Strings = {
     logout: "Sign out",
     admin: "Admin",
     defaultAdminNote:
-      "First run: sign in as the built-in admin (admin / penguin-2026), then change the password soon",
+      "First run: sign in as the built-in admin “admin” with the initial password printed in the server startup output (looks like penguin-1234), then change it soon",
   },
 
   account: {
     changePassword: "Change password",
     oldPassword: "Current password",
-    oldPasswordHint: "The built-in admin's default initial password is penguin-2026",
+    oldPasswordHint:
+      "The built-in admin's initial password is printed in the server startup output (looks like penguin-1234)",
     newPassword: "New password",
     confirmPassword: "Confirm new password",
     passwordMismatch: "New passwords do not match",
@@ -1061,6 +1062,7 @@ Scenarios:
     /** Localized text for the common server error codes (server error messages are English-only); looked up by ApiError.code in apiErrorText, falling back to the raw message for unmapped codes. */
     byCode: {
       invalid_credentials: "Incorrect username or password.",
+      too_many_attempts: "Too many failed sign-in attempts. Try again shortly.",
       password_mismatch: "The current password is incorrect.",
       invalid_password: "Password must be at least 8 characters.",
       admin_required: "Only an admin can perform this operation.",
diff --git a/packages/web/src/lib/strings.ts b/packages/web/src/lib/strings.ts
index 7f47b83..ee8fe18 100644
--- a/packages/web/src/lib/strings.ts
+++ b/packages/web/src/lib/strings.ts
@@ -127,13 +127,14 @@ export const zh = {
     login: "登录",
     logout: "登出",
     admin: "管理员",
-    defaultAdminNote: "首次使用请以内置管理员登录：admin / penguin-2026，登录后请尽快修改密码",
+    defaultAdminNote:
+      "首次使用请以内置管理员 admin 登录，初始密码在服务端首次启动时打印（形如 penguin-1234），登录后请尽快修改密码",
   },
 
   account: {
     changePassword: "修改密码",
     oldPassword: "当前密码",
-    oldPasswordHint: "内置管理员的默认初始密码为 penguin-2026",
+    oldPasswordHint: "内置管理员的初始密码在服务端首次启动时打印（形如 penguin-1234）",
     newPassword: "新密码",
     confirmPassword: "确认新密码",
     passwordMismatch: "两次输入的新密码不一致",
@@ -1040,6 +1041,7 @@ Benchmark：
     /** Localized text for the common server error codes (server error messages are English-only); looked up by ApiError.code in apiErrorText, falling back to the raw message for unmapped codes. */
     byCode: {
       invalid_credentials: "用户名或密码错误。",
+      too_many_attempts: "登录失败次数过多，请稍后重试。",
       password_mismatch: "当前密码不正确。",
       invalid_password: "密码至少 8 位。",
       admin_required: "仅管理员可执行此操作。",