diff --git a/AGENTS.md b/AGENTS.md
index 9e7abca..bfd6591 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -5,6 +5,7 @@ Electron + electron-vite + React 终端工具（本地终端 / SSH / SFTP）。
 ## 常用命令
 
 - 开发：`npm run dev`（主进程改动不热重建，需重启）
+- dev 实例使用独立用户数据目录 `%APPDATA%\OpenTerminal-dev` 与独立单实例锁（`src/main/index.ts` 顶部 `!app.isPackaged` 分支），窗口标题带 `(dev)`：**可与已安装的正式版同时运行，互不干扰**，也不会把测试设置/会话写进真实配置
 - 类型检查：`npx tsc --noEmit -p tsconfig.web.json`
 - 打包：`npm run dist`，产物在 `release/`（msi + exe + latest.yml + blockmap）
   - 国内网络需镜像：`ELECTRON_MIRROR=https://npmmirror.com/mirrors/electron/ ELECTRON_BUILDER_BINARIES_MIRROR=https://npmmirror.com/mirrors/electron-builder-binaries/ npm run dist`
diff --git a/src/main/index.ts b/src/main/index.ts
index 82cd3ca..31c40e3 100644
--- a/src/main/index.ts
+++ b/src/main/index.ts
@@ -20,6 +20,15 @@ function showOrCreate(): void {
   }
 }
 
+// Dev runs get their own userData directory (settings, session snapshot,
+// command history, logs) *and* their own single-instance lock — both are keyed
+// on that path. Without this a dev instance fights the installed build: it
+// takes the lock, so the other side is refused / must be killed, and it writes
+// test data straight into the real profile. Must run before the lock below.
+if (!app.isPackaged) {
+  app.setPath('userData', join(app.getPath('appData'), 'OpenTerminal-dev'))
+}
+
 // Single instance: a second launch just surfaces the existing window (pulls
 // it out of the tray if hidden there) instead of starting another process.
 const gotSingleInstanceLock = app.requestSingleInstanceLock()
@@ -64,6 +73,15 @@ function createWindow(): void {
 
   win.on('ready-to-show', () => win.show())
 
+  // Dev window wears a "(dev)" tag so it is never confused with the installed
+  // build sitting next to it (they no longer share userData — see above).
+  if (!app.isPackaged) {
+    win.on('page-title-updated', (e) => {
+      e.preventDefault()
+      win.setTitle('OpenTerminal (dev)')
+    })
+  }
+
   // Close button → tray / exit per the closeAction setting (ask by default).
   win.on('close', (e) => {
     void onMainWindowClose(win, e, showOrCreate)