diff --git a/README.md b/README.md
index 649d8d5..e6a172d 100644
--- a/README.md
+++ b/README.md
@@ -163,7 +163,7 @@ dsh registry enable dsh-external/dsh-better-sidebar
 | **🗂️ 文件工作台：资源管理器**<br/><sub>支持两种格式的资源管理器：内嵌在文件预览中 / 独立显示文件树。懒加载目录树、软链接按目标类型展示（目录软链接可展开、失效链接标红）、全局文件名搜索、上传文件/文件夹与拖放上传、右键菜单（在新 Tab 打开 / 在侧边打开 / 复制路径）、悬浮 `@文件` 一键引用进输入框。</sub><br/><div align="center"><img width="420" alt="文件资源管理器" src="https://github.com/user-attachments/assets/a410bfd2-a8ba-43e6-873e-22417756e94d" /></div> | **📝 Markdown · 图片 · PDF 内联预览**<br/><sub>Markdown 预览支持 **Mermaid 图表**（`securityLevel: 'strict'` 安全渲染 + 二次清洗；点击图表弹窗放大、滚轮缩放、拖拽平移）、**README 级内嵌 HTML**（徽章墙 `<div align=center>`、`<details>` 折叠块内嵌 markdown、表格单元格内联标签——DOMPurify 白名单消毒真实渲染，`<script>` 等活性内容剥除，本地图片经会话媒体路由重写）与**浮动目录大纲**（≥3 标题出现，点击平滑跳转、自动展开折叠块）；图片 / PDF 走媒体路由内联展示；Office 三件套由生态插件补齐。</sub><br/><div align="center"><img width="420" alt="Markdown + Mermaid 预览" src="https://github.com/user-attachments/assets/fe0e5182-55bb-45cc-b98b-a2877c2bdd38" /></div> |
 | **🖥️ CodeMirror 代码编辑器**<br/><div align="center"><img width="420" alt="CodeMirror 代码编辑器" src="https://github.com/user-attachments/assets/b44b488e-568c-4ee0-b96c-e9c906598a77" /></div> | **🖼️ 图片内联预览**<br/><div align="center"><img width="420" alt="图片内联预览" src="https://github.com/user-attachments/assets/f9a58c30-5b7a-48b5-9e22-37d7e071f593" /></div> |
 | **💻 真实终端**<br/><sub>xterm.js + node-pty 真实 shell（不是模拟器）：断线重连 transcript 回放、shell / shellArgs 可配置（设置页或 `cordis.patch.yml`）、可选为模型注入 `terminal_*` 工具（agent 可直接开终端跑命令）。</sub><br/><div align="center"><img width="420" alt="真实终端" src="https://github.com/user-attachments/assets/0dad6ad3-ff3f-4b5a-86d2-f832ce65323e" /></div> | **🌿 文件变动：Git 视角 + 本轮文件**<br/><sub>双视角合一：**Git 视角**保留完整源代码管理（暂存 / 取消暂存 / 提交（`Ctrl+Enter`）/ 还原、历史、worktree 与子仓库选择）；**本轮文件视角**实时折叠会话事件日志，记录模型读 / 写 / 编辑的每个文件（按文件分组、按类型筛选、操作数角标）。点击任意改动在底部**可拖拽预览面板**查看统一 diff——删红 / 增绿 / 改蓝配对 + 行内字符级高亮 + 语法着色 + 上下文折叠——也可一键展开为 VSCode 式独立 diff tab（同一渲染栈）。</sub><br/><div align="center"><img width="420" alt="文件变动" src="https://github.com/user-attachments/assets/e7fc1220-305f-4bca-8583-e77ab4f4fa78" /></div> |
-| **🌐 内嵌浏览器**<br/><sub>多开网页 tab：后退 / 前进 / 刷新 / 地址栏；内容运行在**不透明源沙箱 iframe**（界面实时显示沙箱状态，可按页面临时解锁）；聊天里的外链点击可被接管到侧边栏打开（按协议分流，可配）。</sub><br/><div align="center"><img width="420" alt="内嵌浏览器" src="https://github.com/user-attachments/assets/9bc6b65a-64fc-4942-a685-76e391e55606" /></div> | **🧩 任务页：子代理拓扑 + 后台任务**<br/><sub>子代理树实时拓扑（运行状态、批量实时预览）+ 后台任务清单（退出码 / 实时输出 / 强制终止）；新子代理 / 新任务可自动展开侧边栏（可关）。</sub><br/><div align="center"><img width="420" alt="任务页：子代理拓扑" src="https://github.com/user-attachments/assets/dcd8ed2f-59fa-405b-937b-2d250f5034dd" /></div> |
+| **🌐 内嵌浏览器**<br/><sub>多开网页 tab：后退 / 前进 / 刷新 / 地址栏；内容运行在**不透明源沙箱 iframe**（界面实时显示沙箱状态，可按页面临时解锁）；聊天里的外链点击可被接管到侧边栏打开（按协议分流，可配）。</sub><br/><div align="center"><img width="420" alt="内嵌浏览器" src="https://github.com/user-attachments/assets/9bc6b65a-64fc-4942-a685-76e391e55606" /></div> | **🧩 任务页：子代理拓扑 + 后台任务**<br/><sub>子代理树实时拓扑（运行状态、批量实时预览）+ 后台任务清单（退出码 / 实时输出 / 强制终止）；新子代理 / 新任务可自动激活任务页，宽屏同时展开侧边栏，窄屏不强制展开全屏抽屉（可关）。</sub><br/><div align="center"><img width="420" alt="任务页：子代理拓扑" src="https://github.com/user-attachments/assets/dcd8ed2f-59fa-405b-937b-2d250f5034dd" /></div> |
 | **💬 侧边对话(beta)**<br/><sub>Codex 风格侧边线程：**每个对话一个独立 Tab**；线程继承主会话完整上下文（含进行中回合，以 interrupted 诚实冻结）独立运行，不污染主会话；可持续追问、重启冷恢复；一键「保存为新会话」提升为顶层会话。</sub><br/><div align="center"><img width="420" alt="侧边对话(beta)" src="https://github.com/user-attachments/assets/3a338c36-f5de-4000-95f3-4b1cd04f60fc" /></div> | **🪟 双工作台：右侧栏 + 底部面板 + 分栏**<br/><sub>右侧栏与底部面板可同时展开；拖 Tab 到分栏边缘**拆分**、拖到中间**合并**（可跨面板）；面板宽高左缘/上缘拖拽调节；移动端自动合并为全宽抽屉；把 tab 拖到主会话区域可变为**自由窗口**（悬浮 / 缩放 / 置顶，拖回 pane 停靠）。</sub><br/><div align="center"><img width="420" alt="双工作台（右侧栏 + 底部面板）" src="https://github.com/user-attachments/assets/dfdb875e-a1a8-4d4b-8340-353736b1708f" /></div> |
 | **⚙️ 声明式设置**<br/><sub>设置页「侧边卡片」分区：每个 tab / 预览器一张小卡片，独立开关（高亮启用态 + 品牌开关滑块）；二级设置经卡片底部「功能设置」条弹窗（开关 / 文本 / 数字 / 下拉）；插件自有设置持久化在 `pluginSettings`。</sub><br/><div align="center"><img width="420" alt="声明式设置：侧边卡片" src="https://github.com/user-attachments/assets/0800ca64-621e-48da-b7df-aecfddc3ec29" /></div> | **📱 移动端**<br/><sub>窄屏（<768px）自动切换为全宽抽屉：底栏 tab 一次性并入右侧栏，触屏拖拽可调。</sub><br/><div align="center"><img width="360" alt="移动端全宽抽屉" src="https://github.com/user-attachments/assets/a82ba78a-f4cf-4d85-80e8-050a05beb144" /></div> |
 
@@ -367,7 +367,7 @@ GitHub topic [`dsh-better-sidebar`](https://github.com/topics/dsh-better-sidebar
 
 - 🖥️ **终端跨会话切换保活**（[#323](https://github.com/omdsh-dev/DSH-better-sidebar/pull/323)）：切到其他会话不再被当作瞬时掉线——客户端卸载时发送 `park` 控制帧，主机跳过 30s 重连宽限倒计时；切回会话（`open()` 取消 parked）或显式关闭恢复正常生命周期；agent 终端保持无限期存活
 - 📂 **文件树上传遮罩不再拦截 Tab 拖拽**（[#317](https://github.com/omdsh-dev/DSH-better-sidebar/pull/317)）：拖拽 Tab（重排 / 跨 pane split）经过资源管理器时不再弹上传遮罩、不吞事件——统一按 `dataTransfer.types` 含 `Files` 门控（与面板宿主 shield 一致），Tab 正常落下；OS 文件拖拽行为不变
-- 💬 **子代理自动展开去抖**（[#314](https://github.com/omdsh-dev/DSH-better-sidebar/pull/314)）：Side Chat 线程创建不再误弹任务页——0→N 触发 500ms 重臂并对实时快照按原基线重评估，标题过滤器识别线程后才放行；真实子代理依然自动展开
+- 💬 **子代理自动展开去抖**（[#314](https://github.com/omdsh-dev/DSH-better-sidebar/pull/314)）：Side Chat 线程创建不再误弹任务页——0→N 触发 500ms 重臂并对实时快照按原基线重评估，标题过滤器识别线程后才放行；真实子代理依然自动激活任务页（宽屏展开侧边栏，窄屏只准备 Tab、不强制展开抽屉）
 
 ### v0.15.0
 
diff --git a/README_EN.md b/README_EN.md
index fa547d6..a2f8810 100644
--- a/README_EN.md
+++ b/README_EN.md
@@ -163,7 +163,7 @@ Update: `git pull && pnpm install && pnpm build` → `node scripts/package-regis
 | **🗂️ File Workbench: Explorer**<br/><sub>Two explorer modes: embedded in the file preview / standalone file tree. Lazy-loading directory tree, symlinks classified by target kind (directory links expand, dangling links flagged), global filename search, file/folder upload buttons plus drag-drop upload, context menu (open in new tab / open to the side / copy paths), and a hover `@file` button that references a file straight into the composer.</sub><br/><div align="center"><img width="420" alt="File explorer" src="https://github.com/user-attachments/assets/a410bfd2-a8ba-43e6-873e-22417756e94d" /></div> | **📝 Inline Preview: Markdown · Images · PDF**<br/><sub>The Markdown preview renders **Mermaid diagrams** (strict-mode safe rendering + a second sanitize pass; click a diagram for a zoom modal with wheel-zoom and drag-pan), **README-level inline HTML** (badge walls `<div align=center>`, `<details>` blocks nesting markdown, inline tags in table cells — DOMPurify-sanitized, `<script>` stripped, local media rewritten to the session media route) and a floating **table of contents** (appears with ≥3 headings, smooth-scroll jumping, auto-expanding folded blocks); images / PDFs display inline via the media route; the Office suite is covered by an ecosystem plugin.</sub><br/><div align="center"><img width="420" alt="Markdown + Mermaid preview" src="https://github.com/user-attachments/assets/fe0e5182-55bb-45cc-b98b-a2877c2bdd38" /></div> |
 | **🖥️ CodeMirror editor**<br/><div align="center"><img width="420" alt="CodeMirror editor" src="https://github.com/user-attachments/assets/b44b488e-568c-4ee0-b96c-e9c906598a77" /></div> | **🖼️ Inline image preview**<br/><div align="center"><img width="420" alt="Inline image preview" src="https://github.com/user-attachments/assets/f9a58c30-5b7a-48b5-9e22-37d7e071f593" /></div> |
 | **💻 Real Terminal**<br/><sub>xterm.js + node-pty real shell (not an emulator): transcript replay on reconnect, configurable shell / shellArgs (settings page or `cordis.patch.yml`), and optional `terminal_*` model tools so the agent can open terminals and run commands itself.</sub><br/><div align="center"><img width="420" alt="Real terminal" src="https://github.com/user-attachments/assets/0dad6ad3-ff3f-4b5a-86d2-f832ce65323e" /></div> | **🌿 Changes: Git lens + This-Session lens**<br/><sub>Two lenses on "what changed?": the **Git lens** keeps the full source-control surface (stage / unstage / commit (`Ctrl+Enter`) / revert, history, worktree and child-repo selectors); the **This Session** lens folds the session event log live, recording every file the model read / wrote / edited (grouped by file, kind-filtered, op-count badge). Clicking any change previews it in the **draggable bottom pane** with the unified diff — del red / add green / mod-blue pairing + intra-line character highlights + syntax coloring + context folding — or expands into a VSCode-style dedicated diff tab (same rendering stack).</sub><br/><div align="center"><img width="420" alt="Changes" src="https://github.com/user-attachments/assets/e7fc1220-305f-4bca-8583-e77ab4f4fa78" /></div> |
-| **🌐 Embedded Browser**<br/><sub>Multiple web tabs with back / forward / reload / address bar; content runs in an **opaque-origin sandboxed iframe** (live sandbox status in the UI, per-page temporary unlock available); external-link clicks in the chat can be taken over into the sidebar (protocol-based routing, configurable).</sub><br/><div align="center"><img width="420" alt="Embedded browser" src="https://github.com/user-attachments/assets/9bc6b65a-64fc-4942-a685-76e391e55606" /></div> | **🧩 Tasks: Agent Topology + Background Jobs**<br/><sub>Live subagent-tree topology (run states, batched live previews) plus the background-jobs list (exit codes / live output / force-kill); new subagents / jobs can auto-expand the sidebar (configurable).</sub><br/><div align="center"><img width="420" alt="Tasks: subagent topology" src="https://github.com/user-attachments/assets/dcd8ed2f-59fa-405b-937b-2d250f5034dd" /></div> |
+| **🌐 Embedded Browser**<br/><sub>Multiple web tabs with back / forward / reload / address bar; content runs in an **opaque-origin sandboxed iframe** (live sandbox status in the UI, per-page temporary unlock available); external-link clicks in the chat can be taken over into the sidebar (protocol-based routing, configurable).</sub><br/><div align="center"><img width="420" alt="Embedded browser" src="https://github.com/user-attachments/assets/9bc6b65a-64fc-4942-a685-76e391e55606" /></div> | **🧩 Tasks: Agent Topology + Background Jobs**<br/><sub>Live subagent-tree topology (run states, batched live previews) plus the background-jobs list (exit codes / live output / force-kill); new subagents / jobs can auto-activate the Tasks page, expanding the sidebar on wide viewports without forcing narrow full-screen drawers open (configurable).</sub><br/><div align="center"><img width="420" alt="Tasks: subagent topology" src="https://github.com/user-attachments/assets/dcd8ed2f-59fa-405b-937b-2d250f5034dd" /></div> |
 | **💬 Side Chat (beta)**<br/><sub>Codex-style side threads: **one independent tab per conversation**; the thread inherits the parent's full context (including the in-progress turn, honestly frozen as "interrupted") and runs independently without polluting the main session; follow-ups survive restarts; one click promotes the thread to a top-level session.</sub><br/><div align="center"><img width="420" alt="Side Chat (beta)" src="https://github.com/user-attachments/assets/3a338c36-f5de-4000-95f3-4b1cd04f60fc" /></div> | **🪟 Dual Workbench: Sidebar + Bottom Panel + Split Panes**<br/><sub>The right sidebar and the bottom panel can stay open together; drag a tab to a pane edge to **split**, to the middle to **merge** (works across panels); panel width/height drag from the left/top edge; on mobile everything merges into a full-width drawer; drag a tab onto the main conversation area to turn it into a **free window** (float / resize / raise, drag back onto a pane to dock).</sub><br/><div align="center"><img width="420" alt="Dual workbench (right sidebar + bottom panel)" src="https://github.com/user-attachments/assets/dfdb875e-a1a8-4d4b-8340-353736b1708f" /></div> |
 | **⚙️ Declarative Settings**<br/><sub>The "Side card" section in DSH settings: one small card per tab / viewer with an independent toggle (highlighted enabled state + brand switch); secondary settings open from the "Feature settings" strip at the card bottom (switch / text / number / select rows); plugin-owned settings persist under `pluginSettings`.</sub><br/><div align="center"><img width="420" alt="Declarative settings: side cards" src="https://github.com/user-attachments/assets/0800ca64-621e-48da-b7df-aecfddc3ec29" /></div> | **📱 Mobile**<br/><sub>On narrow screens (<768px) the panels become a full-width drawer: bottom-panel tabs merge into the sidebar once, with touch-friendly dragging.</sub><br/><div align="center"><img width="360" alt="Mobile full-width drawer" src="https://github.com/user-attachments/assets/a82ba78a-f4cf-4d85-80e8-050a05beb144" /></div> |
 
@@ -371,7 +371,7 @@ All changes since v0.15.0:
 
 - 🖥️ **Terminal pty stays alive across conversation switches** ([#323](https://github.com/omdsh-dev/DSH-better-sidebar/pull/323)): switching sessions is no longer treated as a transient drop — the client sends a `park` control frame on unmount and the host skips the 30s reconnect-grace countdown; switching back (`open()` cancels parked) or explicitly closing the tab resumes the normal lifecycle; agent terminals keep their indefinite lifetime
 - 📂 **File-tree upload overlay no longer intercepts Tab drags** ([#317](https://github.com/omdsh-dev/DSH-better-sidebar/pull/317)): dragging tabs (reorder / cross-pane split) across the explorer no longer shows the upload overlay or swallows the event — gated on `dataTransfer.types` containing `Files` (consistent with the panel-host shield), so tabs land normally; OS file drags behave as before
-- 💬 **Subagent auto-open debounced** ([#314](https://github.com/omdsh-dev/DSH-better-sidebar/pull/314)): Side Chat thread creation no longer pops the task page — the 0→N trigger rearms for 500ms and re-evaluates the original baseline against the live snapshot, by which time the title filter recognizes the thread; genuine subagents still auto-open
+- 💬 **Subagent auto-open debounced** ([#314](https://github.com/omdsh-dev/DSH-better-sidebar/pull/314)): Side Chat thread creation no longer pops the task page — the 0→N trigger rearms for 500ms and re-evaluates the original baseline against the live snapshot, by which time the title filter recognizes the thread; genuine subagents still auto-activate the Tasks page (wide viewports expand the sidebar, while narrow viewports prepare the tab without forcing the drawer open)
 
 ### v0.15.0
 
diff --git a/src/client/Sidebar.tsx b/src/client/Sidebar.tsx
index 10881f9..1c733b7 100644
--- a/src/client/Sidebar.tsx
+++ b/src/client/Sidebar.tsx
@@ -554,8 +554,10 @@ export function Sidebar(props: { ctx: Context; store: SidebarStore }) {
    * Subagent auto-activation: the moment the current conversation spawns its
    * FIRST direct subagent (a 0 → N transition on the list feed), the "auto
    * open" pref is on, and the Subagent tab type is enabled in settings,
-   * open the panel (if collapsed) and focus the Subagent page
-   * (single-instance: an existing tab is focused, never duplicated).
+   * focus the Subagent page (single-instance: an existing tab is focused,
+   * never duplicated). On wide viewports the right panel also expands; on
+   * narrow viewports background activity never forces the full-screen drawer
+   * open over the chat.
    * Switching to a session that already has subagents never triggers — its
    * baseline starts at the current count — so a deliberate layout is never
    * fought.
@@ -581,10 +583,14 @@ export function Sidebar(props: { ctx: Context; store: SidebarStore }) {
       if (!detectNewDirectSubagent(baseline, ctx.sessions.list.getSnapshot(), sessionId)) return
       if (!store.getPrefs().autoOpenSubagent) return
       if (ctx.get('betterSidebar')?.isTabEnabled('subagent') === false) return
-      store.reduce(s => s.panelOpen ? s : togglePanel(s))
-      // Pin the landing to the right panel: the auto-opened Subagent page must
-      // appear where the panel just expanded, not in a bottom-panel pane the
-      // user last touched.
+      // Read the viewport when the delayed activation fires: a resize while
+      // the debounce is armed must not let background activity force the
+      // narrow full-screen drawer open over the chat.
+      if (!isNarrowWidth(window.innerWidth)) {
+        store.reduce(s => s.panelOpen ? s : togglePanel(s))
+      }
+      // Pin the landing to the right panel: the auto-activated Subagent page
+      // must be ready there, not in a bottom-panel pane the user last touched.
       store.reduce(s => ({ ...s, activePane: firstLeaf(s.splits).id }))
       ctx.get('betterSidebar')?.openTab({ type: 'subagent', title: t('subagent') })
     }, AUTO_OPEN_DEBOUNCE_MS)
@@ -601,9 +607,9 @@ export function Sidebar(props: { ctx: Context; store: SidebarStore }) {
   /**
    * Job auto-activation: the moment a NEW background job appears for the
    * current conversation (a job id the previous snapshot lacked), the
-   * auto-open pref is on, and the Jobs tab type is enabled, open the panel
-   * (if collapsed) and focus the Jobs page. Unlike the subagent trigger
-   * (0 → N only), ANY new job id triggers: the agent may start several
+   * auto-open pref is on, and the Jobs tab type is enabled, focus the Jobs
+   * page. The right panel expands only on wide viewports. Unlike the subagent
+   * trigger (0 → N only), ANY new job id triggers: the agent may start several
    * jobs in one session, and each should surface. A fresh page load never
    * triggers — its baseline starts at the current snapshot.
    */
@@ -615,7 +621,9 @@ export function Sidebar(props: { ctx: Context; store: SidebarStore }) {
     if (!detectNewJob(prev, sessionList, sessionId)) return
     if (!store.getPrefs().autoOpenJobs) return
     if (ctx.get('betterSidebar')?.isTabEnabled('subagent') === false) return
-    store.reduce(s => s.panelOpen ? s : togglePanel(s))
+    if (!isNarrowWidth(window.innerWidth)) {
+      store.reduce(s => s.panelOpen ? s : togglePanel(s))
+    }
     store.reduce(s => ({ ...s, activePane: firstLeaf(s.splits).id }))
     ctx.get('betterSidebar')?.openTab({ type: 'subagent', title: t('subagent') })
   }, [sessionList, sessionId, store, ctx])
diff --git a/src/client/locales.ts b/src/client/locales.ts
index 4177b6b..9f4e806 100644
--- a/src/client/locales.ts
+++ b/src/client/locales.ts
@@ -250,10 +250,10 @@ export const zh = {
   settingsConflict: '设置已被其他窗口修改，请重试',
   binaryNoPreview: '此文件类型不支持预览',
   downloadToView: '下载查看',
-  settingsSubagentTitle: '检测到子代理时自动展开任务管理页',
-  settingsSubagentDesc: '当前会话产生新的子代理时，自动展开侧边栏并打开任务管理页；关闭后需手动打开',
-  settingsJobsTitle: '有新后台任务时自动展开后台任务页',
-  settingsJobsDesc: '当前会话出现新的后台任务时，自动展开侧边栏并打开后台任务页（每个新任务都会触发）；关闭后需手动打开',
+  settingsSubagentTitle: '检测到子代理时自动激活任务管理页',
+  settingsSubagentDesc: '当前会话产生新的子代理时，自动激活任务管理页；宽屏同时展开侧边栏，窄屏不强制展开全屏抽屉；关闭后需手动打开',
+  settingsJobsTitle: '有新后台任务时自动激活后台任务页',
+  settingsJobsDesc: '当前会话出现新的后台任务时，自动激活后台任务页（每个新任务都会触发）；宽屏同时展开侧边栏，窄屏不强制展开全屏抽屉；关闭后需手动打开',
   settingsToolsTitle: '为模型注入终端工具',
   settingsToolsDesc: '开启后，模型可通过 terminal_create 等 8 个工具创建并操作侧边栏终端（默认关闭）',
   settingsFenceTitle: '工作区路径检测',
@@ -659,10 +659,10 @@ export const en: Record<keyof typeof zh, string> = {
   settingsConflict: 'The setting changed in another window — please retry',
   binaryNoPreview: 'This file type cannot be previewed',
   downloadToView: 'Download to view',
-  settingsSubagentTitle: 'Auto-open the Tasks page when a subagent appears',
-  settingsSubagentDesc: 'Expand the side card and open the Tasks page when the current conversation spawns a new subagent; turn off to open it manually',
-  settingsJobsTitle: 'Auto-open the Jobs page on a new background job',
-  settingsJobsDesc: 'Expand the side card and open the Jobs page whenever a new background job appears for the current conversation (every new job triggers); turn off to open it manually',
+  settingsSubagentTitle: 'Auto-activate the Tasks page when a subagent appears',
+  settingsSubagentDesc: 'Activate the Tasks page when the current conversation spawns a new subagent; wide viewports also expand the side card, while narrow full-screen drawers are not forced open; turn off to open it manually',
+  settingsJobsTitle: 'Auto-activate the Jobs page on a new background job',
+  settingsJobsDesc: 'Activate the Jobs page whenever a new background job appears for the current conversation (every new job triggers); wide viewports also expand the side card, while narrow full-screen drawers are not forced open; turn off to open it manually',
   settingsToolsTitle: 'Inject terminal tools for the model',
   settingsToolsDesc: 'When enabled, the model can create and drive sidebar terminals through the 8 terminal_* tools (off by default)',
   settingsFenceTitle: 'Workspace path fence',
diff --git a/src/prefs-shared.ts b/src/prefs-shared.ts
index a40a212..0042020 100644
--- a/src/prefs-shared.ts
+++ b/src/prefs-shared.ts
@@ -16,14 +16,16 @@ export interface SidebarPrefs {
   /** Default panel width as a percent of the window width (20–60). */
   defaultWidthPercent: number
   /**
-   * Whether the sidebar auto-activates (opens the panel) and expands the
-   * Subagent page when the current conversation spawns a new subagent.
+   * Whether the sidebar auto-activates the Subagent page when the current
+   * conversation spawns a new subagent. Wide viewports also open the panel;
+   * narrow viewports prepare the tab without opening the full-screen drawer.
    */
   autoOpenSubagent: boolean
   /**
-   * Whether the sidebar auto-activates (opens the panel) and expands the
-   * Jobs page when a NEW background job appears for the current
-   * conversation (any new job id, not just the first one).
+   * Whether the sidebar auto-activates the Jobs page when a NEW background
+   * job appears for the current conversation (any new job id, not just the
+   * first one). Wide viewports also open the panel; narrow viewports prepare
+   * the tab without opening the full-screen drawer.
    */
   autoOpenJobs: boolean
   /**
diff --git a/tests/sidebar-auto-activation.spec.tsx b/tests/sidebar-auto-activation.spec.tsx
new file mode 100644
index 0000000..a90d1a6
--- /dev/null
+++ b/tests/sidebar-auto-activation.spec.tsx
@@ -0,0 +1,194 @@
+/**
+ * Real-Sidebar regressions for issue #162: background activity should focus
+ * the Subagent page on every viewport, but a narrow full-screen drawer must
+ * stay folded until the user chooses to open it.
+ */
+// @vitest-environment jsdom
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
+import { createElement } from 'react'
+import { createRoot, type Root } from 'react-dom/client'
+import { act } from 'react-dom/test-utils'
+
+;(globalThis as Record<string, unknown>).IS_REACT_ACT_ENVIRONMENT = true
+
+import { Sidebar } from '../src/client/Sidebar.tsx'
+import { allLeaves, createSidebarStore, firstLeaf, type SidebarStore } from '../src/client/state.ts'
+import { createBetterSidebarService, type BetterSidebarService } from '../src/client/service.ts'
+import type { Context, SidebarSessionList } from '../src/context-types.ts'
+
+class FakeWebSocket {
+  onmessage: ((event: { data: unknown }) => void) | null = null
+  onclose: (() => void) | null = null
+  onerror: (() => void) | null = null
+  close = (): void => {}
+  constructor(_url: string) {}
+}
+
+function makeSessionFeed(initial: SidebarSessionList) {
+  let snapshot = initial
+  const listeners = new Set<() => void>()
+  return {
+    getSnapshot: () => snapshot,
+    subscribe: (listener: () => void) => {
+      listeners.add(listener)
+      return () => { listeners.delete(listener) }
+    },
+    set(next: SidebarSessionList): void {
+      snapshot = next
+      for (const listener of [...listeners]) listener()
+    },
+  }
+}
+
+type SessionFeed = ReturnType<typeof makeSessionFeed>
+
+interface MountedSidebar {
+  store: SidebarStore
+  service: BetterSidebarService
+  feed: SessionFeed
+  unmount: () => void
+}
+
+let sessionSeq = 0
+const mounted: MountedSidebar[] = []
+
+function setViewport(width: number): void {
+  Object.defineProperty(window, 'innerWidth', { configurable: true, value: width })
+}
+
+function mountSidebar(width: number): MountedSidebar {
+  setViewport(width)
+  vi.stubGlobal('WebSocket', FakeWebSocket)
+  const sessionId = `auto-activation-${++sessionSeq}`
+  const initial: SidebarSessionList = {
+    current: sessionId,
+    byId: {
+      [sessionId]: { id: sessionId, cwd: '/tmp', displayTitle: 'Root' },
+    },
+    jobsBySession: { [sessionId]: [] },
+  }
+  const feed = makeSessionFeed(initial)
+  const store = createSidebarStore()
+  store.setPrefs({ ...store.getPrefs(), autoOpenSubagent: true, autoOpenJobs: true })
+  store.setSession(sessionId)
+  store.reduce(state => ({ ...state, panelOpen: false }))
+  const service = createBetterSidebarService(store)
+  service.registerTab({ id: 'subagent', title: 'Subagent', component: () => null })
+  const localeSnapshot = { active: 'en' }
+  const ctx = {
+    locale: { subscribe: () => () => {}, getSnapshot: () => localeSnapshot },
+    sessions: { list: feed },
+    betterSidebar: service,
+    get: (name: string) => name === 'betterSidebar' ? service : undefined,
+  } as unknown as Context
+  const container = document.createElement('div')
+  document.body.append(container)
+  const root: Root = createRoot(container)
+  act(() => { root.render(createElement(Sidebar, { ctx, store })) })
+  const result = {
+    store,
+    service,
+    feed,
+    unmount: () => {
+      act(() => { root.unmount() })
+      container.remove()
+    },
+  }
+  mounted.push(result)
+  return result
+}
+
+function publishSubagent(sidebar: MountedSidebar): void {
+  const before = sidebar.feed.getSnapshot()
+  const sessionId = before.current!
+  act(() => {
+    sidebar.feed.set({
+      ...before,
+      byId: {
+        ...before.byId,
+        child: {
+          id: 'child',
+          displayTitle: 'Worker',
+          origin: 'subagent',
+          parentId: sessionId,
+          running: true,
+        },
+      },
+    })
+  })
+}
+
+function flushSubagentDebounce(): void {
+  act(() => { vi.advanceTimersByTime(500) })
+}
+
+function publishJob(sidebar: MountedSidebar): void {
+  const before = sidebar.feed.getSnapshot()
+  const sessionId = before.current!
+  act(() => {
+    sidebar.feed.set({
+      ...before,
+      jobsBySession: {
+        ...before.jobsBySession,
+        [sessionId]: [{
+          id: 'bash-1',
+          kind: 'bash',
+          label: 'sleep 30',
+          status: 'running',
+          startedAt: 1_000,
+        }],
+      },
+    })
+  })
+}
+
+function expectSubagentFocused(sidebar: MountedSidebar, panelOpen: boolean): void {
+  const state = sidebar.store.getSnapshot().state!
+  const right = firstLeaf(state.splits)
+  expect(state.panelOpen).toBe(panelOpen)
+  expect(state.activePane).toBe(right.id)
+  expect(allLeaves(state.splits).flatMap(leaf => leaf.tabs)
+    .filter(tab => tab.type === 'subagent')).toHaveLength(1)
+  expect(right.tabs.find(tab => tab.id === right.active)?.type).toBe('subagent')
+}
+
+beforeEach(() => {
+  vi.useFakeTimers()
+  localStorage.clear()
+})
+
+afterEach(() => {
+  while (mounted.length > 0) mounted.pop()!.unmount()
+  vi.clearAllTimers()
+  vi.useRealTimers()
+  vi.unstubAllGlobals()
+  localStorage.clear()
+  document.body.innerHTML = ''
+  setViewport(1024)
+})
+
+describe('Sidebar background-activity auto-activation (#162)', () => {
+  it.each([
+    { source: 'subagent', width: 390, opens: false },
+    { source: 'job', width: 390, opens: false },
+    { source: 'subagent', width: 1024, opens: true },
+    { source: 'job', width: 1024, opens: true },
+  ] as const)('$source activation at $width px sets panelOpen=$opens', ({ source, width, opens }) => {
+    const sidebar = mountSidebar(width)
+    if (source === 'subagent') {
+      publishSubagent(sidebar)
+      flushSubagentDebounce()
+    } else {
+      publishJob(sidebar)
+    }
+    expectSubagentFocused(sidebar, opens)
+  })
+
+  it('uses the current viewport when the delayed subagent activation fires', () => {
+    const sidebar = mountSidebar(1024)
+    publishSubagent(sidebar)
+    setViewport(390)
+    flushSubagentDebounce()
+    expectSubagentFocused(sidebar, false)
+  })
+})