diff --git a/AGENTS.md b/AGENTS.md
index 4364695b5..6d923155e 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -181,7 +181,7 @@ interface TabDescriptor {
    */
   settings?: {
     toggles?: readonly {
-      /** SidebarPrefs 字段名（内置键：'autoOpenSubagent' / 'agentTerminalTools' / 'agentOpenTools' / 'terminalFontFamily' / 'editorExplorer' / 'htmlViewerNoSandbox' / 'htmlViewerDefaultUnsafe' / 'browserNoSandbox' / 'browserInterceptLinks' / 'browserInterceptHttp' / 'browserInterceptHttps'） */
+      /** SidebarPrefs 字段名（内置键：'autoOpenSubagent' / 'hideCompletedSubagents' / 'agentTerminalTools' / 'agentOpenTools' / 'terminalFontFamily' / 'editorExplorer' / 'htmlViewerNoSandbox' / 'htmlViewerDefaultUnsafe' / 'browserNoSandbox' / 'browserInterceptLinks' / 'browserInterceptHttp' / 'browserInterceptHttps'） */
       key: string
       title: string | (() => string)
       desc?: string | (() => string)
@@ -571,7 +571,7 @@ interface OpenTabSeed {
 }
 ```
 
-> **声明式设置（v0.4.1+）**：每个注册的 tab/viewer 自动出现在 DSH 设置页「侧边卡片」分区的清单里——响应式网格中的**小卡片**（图标 + 标题 + 类型 id + **高亮 = 启用**，启用卡片最右端渲染紧凑品牌开关滑块，viewer 卡片还显示扩展名），开关持久化到 `SidebarPrefs.tabsEnabled / viewersEnabled`（开放 map，缺省 = 启用）。关闭语义：tab 从 `+` 菜单消失、`openTab` 拒绝新开、子代理自动展开 / agent 终端自动补 tab 等派生流程停止，**已打开的 tab 保留**；viewer 被 `matchFileViewer` 跳过，文件落到下一个匹配。`settings.toggles` 声明的相关设置（如子代理的 `autoOpenSubagent`、终端的 `terminalFontFamily`/`terminalFontSize`）通过卡片底部的「功能设置」设置条（齿轮图标 + 文字标签，hairline 分隔）在**原生弹窗**中编辑——`type: 'switch'` 行是复选框，`type: 'text'`/`'number'` 行是输入框（v0.11.0+），`type: 'select'` 行是下拉选择（options 带 icon 时为大图标选项卡，`multi: true` 多选存 value 数组）——父级卡片关闭时设置条隐藏；`settings.toggles` 的 **key 必须是宿主 PrefsSchema 的字段**（内置键：`autoOpenSubagent` / `agentTerminalTools` / `agentOpenTools` / `terminalFontFamily` / `terminalFontSize` / `editorExplorer` / `htmlViewerNoSandbox` / `htmlViewerDefaultUnsafe` / `browserNoSandbox` / `browserInterceptLinks` / `browserInterceptHttp` / `browserInterceptHttps`）。**v0.12.0 起设置 seam 已开放**：外部插件用 `settings.pluginToggles`（同款行控件，key 插件局部）或 `settings.render`（自定义面板）声明自己的设置，值持久化在 prefs 文档的 `pluginSettings[<descriptor id>]`（开放 map，宿主 schema 已有字段，无需注册）——设置弹窗对 tab 与 viewer 都可用（viewer 卡片 v0.12.0 起也有设置条）。
+> **声明式设置（v0.4.1+）**：每个注册的 tab/viewer 自动出现在 DSH 设置页「侧边卡片」分区的清单里——响应式网格中的**小卡片**（图标 + 标题 + 类型 id + **高亮 = 启用**，启用卡片最右端渲染紧凑品牌开关滑块，viewer 卡片还显示扩展名），开关持久化到 `SidebarPrefs.tabsEnabled / viewersEnabled`（开放 map，缺省 = 启用）。关闭语义：tab 从 `+` 菜单消失、`openTab` 拒绝新开、子代理自动展开 / agent 终端自动补 tab 等派生流程停止，**已打开的 tab 保留**；viewer 被 `matchFileViewer` 跳过，文件落到下一个匹配。`settings.toggles` 声明的相关设置（如子代理的 `autoOpenSubagent` / `hideCompletedSubagents`、终端的 `terminalFontFamily`/`terminalFontSize`）通过卡片底部的「功能设置」设置条（齿轮图标 + 文字标签，hairline 分隔）在**原生弹窗**中编辑——`type: 'switch'` 行是复选框，`type: 'text'`/`'number'` 行是输入框（v0.11.0+），`type: 'select'` 行是下拉选择（options 带 icon 时为大图标选项卡，`multi: true` 多选存 value 数组）——父级卡片关闭时设置条隐藏；`settings.toggles` 的 **key 必须是宿主 PrefsSchema 的字段**（内置键：`autoOpenSubagent` / `hideCompletedSubagents` / `agentTerminalTools` / `agentOpenTools` / `terminalFontFamily` / `terminalFontSize` / `editorExplorer` / `htmlViewerNoSandbox` / `htmlViewerDefaultUnsafe` / `browserNoSandbox` / `browserInterceptLinks` / `browserInterceptHttp` / `browserInterceptHttps`）。**v0.12.0 起设置 seam 已开放**：外部插件用 `settings.pluginToggles`（同款行控件，key 插件局部）或 `settings.render`（自定义面板）声明自己的设置，值持久化在 prefs 文档的 `pluginSettings[<descriptor id>]`（开放 map，宿主 schema 已有字段，无需注册）——设置弹窗对 tab 与 viewer 都可用（viewer 卡片 v0.12.0 起也有设置条）。
 
 ---
 
diff --git a/README.md b/README.md
index 80aa034e1..23615c519 100644
--- a/README.md
+++ b/README.md
@@ -159,7 +159,7 @@ 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> | **🌿 Git 面板**<br/><sub>暂存 / 取消暂存 / 提交（`Ctrl+Enter`）/ 还原，历史列表；点击改动文件打开 **VSCode 式 diff tab**（红绿行级对比）。</sub><br/><div align="center"><img width="420" alt="Git 面板" 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）并默认开启「仅活跃」筛选 + 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> |
 | **💬 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。</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> |
 
diff --git a/README_EN.md b/README_EN.md
index 9b641d970..be279f6cf 100644
--- a/README_EN.md
+++ b/README_EN.md
@@ -159,7 +159,7 @@ 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); 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> | **🌿 Git Panel**<br/><sub>Stage / unstage / commit (`Ctrl+Enter`) / revert, plus a history list; clicking a changed file opens a **VSCode-style diff tab** (line-level red/green).</sub><br/><div align="center"><img width="420" alt="Git panel" 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) with an enabled-by-default **Active only** switch, 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> |
 | **💬 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.</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> |
 
diff --git a/docs/external-plugin-guide.md b/docs/external-plugin-guide.md
index 46bb83071..d2c98bb05 100644
--- a/docs/external-plugin-guide.md
+++ b/docs/external-plugin-guide.md
@@ -608,7 +608,7 @@ ctx.effect(() =>
 - 展示：小卡片网格（图标 + 标题 + 类型 id），**高亮 = 启用**，勾选徽标钉在卡片最右端；viewer 卡片额外显示扩展名。
 - 持久化：开关写入 `SidebarPrefs.tabsEnabled / viewersEnabled`（开放 map，**缺省 = 启用**，显式 `false` 才禁用）。
 - 关闭语义：tab 从 `+` 菜单消失、`openTab` 拒绝新开（`console.warn`）、派生流程（子代理自动展开、agent 终端自动补 tab）停止，**已打开的 tab 保留**；viewer 被 `matchFileViewer` 跳过，文件落到下一个匹配。
-- `settings.toggles`（可选）：在卡片行下追加**嵌套设置行**（仅父级启用时显示），绑定 `SidebarPrefs` 字段；通过卡片右下角齿轮按钮在原生弹窗中编辑。行控件 v0.11.0 起不限于布尔：`type: 'switch' | 'text' | 'number'`（缺省 'switch'；text/number 行 blur/Enter 提交，number 行按 min/max 钳制，unit 渲染单位后缀）。内置示例：subagent tab 的 `autoOpenSubagent`、terminal tab 的 `agentTerminalTools` + 自定义字体行。
+- `settings.toggles`（可选）：在卡片行下追加**嵌套设置行**（仅父级启用时显示），绑定 `SidebarPrefs` 字段；通过卡片右下角齿轮按钮在原生弹窗中编辑。行控件 v0.11.0 起不限于布尔：`type: 'switch' | 'text' | 'number'`（缺省 'switch'；text/number 行 blur/Enter 提交，number 行按 min/max 钳制，unit 渲染单位后缀）。内置示例：subagent tab 的 `autoOpenSubagent` / `hideCompletedSubagents`、terminal tab 的 `agentTerminalTools` + 自定义字体行。
 - `settings.pluginToggles`（可选，v0.12.0+）：**插件自有设置行**，行控件与 toggles 相同，但 key 是插件局部的——持久化在 prefs 文档的 `pluginSettings[<descriptor id>]`（开放 map，无需宿主 schema 字段）。tab 与 viewer 都可用（v0.12.0 起 viewer 卡片也有齿轮按钮）。
 - `settings.render`（可选，v0.12.0+）：**自定义设置面板**——给出时齿轮弹窗渲染它而非行列表。props 含 store/service/prefs、本 descriptor 的 `pluginSettings` blob、`updatePluginSetting(key, value)` 与 `close()`；抛错会被吞掉并显示内联错误。
 
@@ -648,7 +648,7 @@ ctx.effect(() =>
 )
 ```
 
-> ⚠️ **`toggles` 的 key 必须是宿主 PrefsSchema 的字段**（内置键：`autoOpenSubagent` / `agentTerminalTools` / `terminalFontFamily` / `terminalFontSize` / `htmlViewerNoSandbox` / `htmlViewerDefaultUnsafe` / `browserNoSandbox` / `browserInterceptLinks`）。**v0.12.0 起设置 seam 已开放**：你自己的设置走 `pluginToggles`（声明式行）或 `render`（自定义面板），值持久化在 `pluginSettings[id]`——不再需要宿主 schema 字段，也不再被 seam 丢弃。值须 JSON 可序列化（行控件只产出 string/number/boolean；自定义面板自行负责）。
+> ⚠️ **`toggles` 的 key 必须是宿主 PrefsSchema 的字段**（内置键：`autoOpenSubagent` / `hideCompletedSubagents` / `agentTerminalTools` / `terminalFontFamily` / `terminalFontSize` / `htmlViewerNoSandbox` / `htmlViewerDefaultUnsafe` / `browserNoSandbox` / `browserInterceptLinks`）。**v0.12.0 起设置 seam 已开放**：你自己的设置走 `pluginToggles`（声明式行）或 `render`（自定义面板），值持久化在 `pluginSettings[id]`——不再需要宿主 schema 字段，也不再被 seam 丢弃。值须 JSON 可序列化（行控件只产出 string/number/boolean；自定义面板自行负责）。
 
 ---
 
diff --git a/src/client/SubagentView.module.css b/src/client/SubagentView.module.css
index 14ddd9b3c..fdcf406f6 100644
--- a/src/client/SubagentView.module.css
+++ b/src/client/SubagentView.module.css
@@ -34,6 +34,78 @@
   color: var(--dsw-alias-label-tertiary);
 }
 
+/* Enabled-by-default active-only filter. It is a real switch button rather
+   than a hidden preference so the Tasks view always explains why settled
+   rows are absent and lets the user restore them in one click. */
+.subagentFilter {
+  flex: none;
+  display: inline-flex;
+  align-items: center;
+  gap: 5px;
+  min-width: 0;
+  height: 24px;
+  padding: 0 5px;
+  border: none;
+  border-radius: 6px;
+  background: transparent;
+  color: var(--dsw-alias-label-tertiary);
+  font: var(--dsw-font-xxxs-11);
+  cursor: pointer;
+  outline: none;
+}
+
+.subagentFilter:hover,
+.subagentFilter:focus-visible {
+  background: var(--dsw-alias-interactive-bg-hover);
+  color: var(--dsw-alias-label-secondary);
+}
+
+.subagentFilterTrack {
+  position: relative;
+  flex: none;
+  width: 22px;
+  height: 12px;
+  border-radius: 999px;
+  border: 1px solid var(--dsw-alias-border-l2);
+  box-sizing: border-box;
+  background: var(--dsw-alias-bg-layer-2);
+  transition: background 120ms ease, border-color 120ms ease;
+}
+
+.subagentFilterThumb {
+  position: absolute;
+  top: 2px;
+  left: 2px;
+  width: 8px;
+  height: 8px;
+  border-radius: 50%;
+  background: var(--dsw-alias-label-tertiary);
+  transition: transform 120ms ease, background 120ms ease;
+}
+
+.subagentFilterActive .subagentFilterTrack {
+  border-color: var(--dsw-alias-button-primary-fill);
+  background: var(--dsw-alias-button-primary-fill);
+}
+
+.subagentFilterActive .subagentFilterThumb {
+  transform: translateX(10px);
+  background: var(--dsw-alias-bg-layer-3);
+}
+
+.subagentFilterLabel {
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+}
+
+@media (prefers-reduced-motion: reduce) {
+  .subagentFilterTrack,
+  .subagentFilterThumb {
+    transition: none;
+  }
+}
+
 .subagentRefresh {
   flex: none;
   display: inline-flex;
diff --git a/src/client/SubagentView.tsx b/src/client/SubagentView.tsx
index 5ea2f744c..55da48f4a 100644
--- a/src/client/SubagentView.tsx
+++ b/src/client/SubagentView.tsx
@@ -38,6 +38,7 @@ import type {
 import {
   collectBranchIds,
   countSubagentDescendants,
+  hasActiveSubagentBranch,
   isSideThreadSummary,
   rootAncestor,
 } from './subagent-detect.ts'
@@ -53,6 +54,8 @@ import {
   type TreeJob,
 } from './subagent-jobs.ts'
 import { api, type JobOutputResult } from './api.ts'
+import type { SidebarStore } from './state.ts'
+import { updateSidebarPrefs } from './plugin-settings.ts'
 import { IconStopOutline16 } from './icons.tsx'
 import { t } from './locales.ts'
 import css from './SubagentView.module.css'
@@ -240,24 +243,42 @@ interface RowsProps {
   currentSessionId: string
   /** The batch live-preview map (child id → latest activity). */
   live: Readonly<Record<string, LastActivity>>
+  /** Hide settled child branches while preserving ancestors of live descendants. */
+  activeOnly: boolean
   openChild: (address: SidebarSubagentAddress) => void
   refresh: (parentSessionId: string) => void
 }
 
+/** Apply the Tasks visibility policy to one catalog row. */
+function catalogEntryVisible(
+  entry: SidebarSubagentChildEntry | SidebarSubagentDiagnosticEntry,
+  catalogs: Readonly<Record<string, SidebarSubagentCatalog>>,
+  byId: Readonly<Record<string, SidebarSessionSummary>>,
+  currentSessionId: string,
+  activeOnly: boolean,
+): boolean {
+  if (entry.kind === 'child') {
+    if (entry.label?.startsWith(SIDE_LABEL_PREFIX) ?? false) return false
+    return !activeOnly || hasActiveSubagentBranch(entry, catalogs, byId, currentSessionId)
+  }
+  // Diagnostics are not completed subagents. Keep them visible so filtering
+  // never conceals a corrupt/unavailable branch that needs attention.
+  return !(byId[entry.id]?.displayTitle.startsWith(SIDE_LABEL_PREFIX) ?? false)
+}
+
 /** Render one topology level; branches are always expanded (lazy catalogs). */
 function CatalogRows({
   parentSessionId, catalog, catalogs, byId, level, currentSessionId, live,
-  openChild, refresh,
+  activeOnly, openChild, refresh,
 }: RowsProps) {
   const emptyLoading = catalog?.state === 'loading' && catalog.entries.length === 0
   // Side Chat threads are honest catalog citizens (durable descriptor, 'Side: '
   // label) but they are NOT subagent topology — filter them out here (the tab
   // strip owns them). Legacy threads created before the descriptor fix still
   // arrive as corrupt diagnostics; they are recognized by summary title.
-  const visibleEntries = (catalog?.entries ?? []).filter((entry) => {
-    if (entry.kind === 'child') return !(entry.label?.startsWith(SIDE_LABEL_PREFIX) ?? false)
-    return !(byId[entry.id]?.displayTitle.startsWith(SIDE_LABEL_PREFIX) ?? false)
-  })
+  const visibleEntries = (catalog?.entries ?? []).filter(entry => (
+    catalogEntryVisible(entry, catalogs, byId, currentSessionId, activeOnly)
+  ))
   return (
     <>
       {emptyLoading && (
@@ -361,6 +382,7 @@ function CatalogRows({
                       level={level + 1}
                       currentSessionId={currentSessionId}
                       live={live}
+                      activeOnly={activeOnly}
                       openChild={openChild}
                       refresh={refresh}
                     />
@@ -643,10 +665,32 @@ export function SubagentView(props: {
   sessionId: string
   active: boolean
   ctx: Context
+  /** Shared sidebar store: present in the built-in tab, optional in isolated tests. */
+  store?: SidebarStore
   onOpenChild?: (address: SidebarSubagentAddress) => void
 }) {
-  const { sessionId, active, ctx, onOpenChild } = props
+  const { sessionId, active, ctx, store, onOpenChild } = props
   const sessions = ctx.sessions
+  const readActiveOnly = useCallback((): boolean => (
+    store?.getPrefs().hideCompletedSubagents ?? true
+  ), [store])
+  const [activeOnly, setActiveOnly] = useState(readActiveOnly)
+
+  // Keep the in-view control synchronized with settings writes from any
+  // surface. Missing/legacy values intentionally resolve to the default ON.
+  useEffect(() => {
+    if (store === undefined) return
+    const sync = (): void => { setActiveOnly(readActiveOnly()) }
+    sync()
+    return store.subscribe(sync)
+  }, [store, readActiveOnly])
+
+  const toggleActiveOnly = useCallback((): void => {
+    const next = !activeOnly
+    setActiveOnly(next)
+    if (store === undefined) return
+    updateSidebarPrefs(store, { hideCompletedSubagents: next })
+  }, [activeOnly, store])
 
   // The same list feed the official catalog consumes (byId lineage + the
   // lazy per-parent catalogs). Older DSH snapshots without the subagent seam
@@ -752,6 +796,13 @@ export function SubagentView(props: {
     : totals.runningCount > 0
       ? t('subagentCountRunning', { count: totals.count, running: totals.runningCount })
       : t('subagentCount', { count: totals.count })
+  const filteredEmpty = activeOnly
+    && totals.count > 0
+    && rootCatalog?.state === 'ready'
+    && !summaryBackedLoading
+    && rootCatalog.entries.every(entry => (
+      !catalogEntryVisible(entry, catalogs, byId, sessionId, activeOnly)
+    ))
 
   /** Arrow-key tree navigation over the visible rows (official catalog recipe). */
   const bodyRef = useRef<HTMLDivElement>(null)
@@ -791,6 +842,19 @@ export function SubagentView(props: {
             ? ` · ${rootSummary.displayTitle}`
             : ''}
         </span>
+        <button
+          type="button"
+          role="switch"
+          aria-checked={activeOnly}
+          title={t('subagentActiveOnlyDesc')}
+          className={clsx(css.subagentFilter, activeOnly && css.subagentFilterActive)}
+          onClick={toggleActiveOnly}
+        >
+          <span className={css.subagentFilterTrack} aria-hidden="true">
+            <span className={css.subagentFilterThumb} />
+          </span>
+          <span className={css.subagentFilterLabel}>{t('subagentActiveOnly')}</span>
+        </button>
         {countLabel !== undefined && <span className={css.subagentCount}>{countLabel}</span>}
         <button
           type="button"
@@ -858,12 +922,19 @@ export function SubagentView(props: {
                   level={1}
                   currentSessionId={sessionId}
                   live={live}
+                  activeOnly={activeOnly}
                   openChild={openChild}
                   refresh={refresh}
                 />
               )}
             </div>
           )}
+          {filteredEmpty && (
+            <div className={css.subagentEmpty}>
+              <div>{t('subagentActiveOnly')}</div>
+              <div className={css.subagentEmptyHint}>{t('subagentActiveOnlyDesc')}</div>
+            </div>
+          )}
           {readyEmpty && (
             <div className={css.subagentEmpty}>
               <div>{t('subagentEmpty')}</div>
diff --git a/src/client/builtins/tabs.tsx b/src/client/builtins/tabs.tsx
index f66ea1dc7..c7a3b4bf9 100644
--- a/src/client/builtins/tabs.tsx
+++ b/src/client/builtins/tabs.tsx
@@ -159,16 +159,21 @@ export function builtinTabs(ctx: Context, options: BuiltinTabOptions = {}): read
           key: 'autoOpenSubagent',
           title: () => t('settingsSubagentTitle'),
           desc: () => t('settingsSubagentDesc'),
+        }, {
+          key: 'hideCompletedSubagents',
+          title: () => t('subagentActiveOnly'),
+          desc: () => t('subagentActiveOnlyDesc'),
         }, {
           key: 'autoOpenJobs',
           title: () => t('settingsJobsTitle'),
           desc: () => t('settingsJobsDesc'),
         }],
       },
-      component: ({ ctx, scope, visible, onSubagentJump }) => (
+      component: ({ ctx, store, scope, visible, onSubagentJump }) => (
         <SubagentView
           sessionId={scope.sessionId}
           ctx={ctx}
+          store={store}
           active={visible}
           onOpenChild={(address) => { onSubagentJump?.(address.childSessionId) }}
         />
diff --git a/src/client/locales-ar.ts b/src/client/locales-ar.ts
index 3ddcb68d5..1c374717c 100644
--- a/src/client/locales-ar.ts
+++ b/src/client/locales-ar.ts
@@ -275,6 +275,8 @@ export const ar: Record<string, string> = {
   subagentEmptyDesc: 'الوكلاء الفرعيون المُنتَجون تحت الوكيل الرئيسي سيظهرون هنا',
   subagentRunning: 'قيد التشغيل',
   subagentInactive: 'خامل',
+  subagentActiveOnly: 'النشطة فقط',
+  subagentActiveOnlyDesc: 'إخفاء الوكلاء الفرعيين المكتملين أو غير النشطين',
   subagentModeOneShot: 'مرة واحدة',
   subagentModeContinuable: 'قابل للاستئناف',
   subagentCount: '{count} وكلاء فرعيون',
diff --git a/src/client/locales-de.ts b/src/client/locales-de.ts
index 30add5a96..15ac0158d 100644
--- a/src/client/locales-de.ts
+++ b/src/client/locales-de.ts
@@ -260,6 +260,8 @@ export const de: Record<string, string> = {
   subagentEmptyDesc: 'Subagenten, die unter dem Hauptagenten erzeugt werden, erscheinen hier',
   subagentRunning: 'Läuft',
   subagentInactive: 'Inaktiv',
+  subagentActiveOnly: 'Nur aktive',
+  subagentActiveOnlyDesc: 'Abgeschlossene oder inaktive Subagenten ausblenden',
   subagentModeOneShot: 'Einmalig',
   subagentModeContinuable: 'Fortsetzbar',
   subagentCount: '{count} Subagenten',
diff --git a/src/client/locales-fr.ts b/src/client/locales-fr.ts
index 6b2d54b24..9e64c31f9 100644
--- a/src/client/locales-fr.ts
+++ b/src/client/locales-fr.ts
@@ -267,6 +267,8 @@ export const fr: Record<string, string> = {
   subagentEmptyDesc: 'Les sous-agents dérivés de l’agent principal actuel s’afficheront ici',
   subagentRunning: 'En cours',
   subagentInactive: 'Inactif',
+  subagentActiveOnly: 'Actifs uniquement',
+  subagentActiveOnlyDesc: 'Masquer les sous-agents terminés ou inactifs',
   subagentModeOneShot: 'À usage unique',
   subagentModeContinuable: 'Reprenable',
   subagentCount: '{count} sous-agent(s)',
diff --git a/src/client/locales-hi.ts b/src/client/locales-hi.ts
index 07d781b4d..235d60392 100644
--- a/src/client/locales-hi.ts
+++ b/src/client/locales-hi.ts
@@ -274,6 +274,8 @@ export const hi: Record<string, string> = {
   subagentEmptyDesc: 'मुख्य एजेंट के अंतर्गत बने सबएजेंट यहाँ दिखेंगे',
   subagentRunning: 'चल रहा',
   subagentInactive: 'निष्क्रिय',
+  subagentActiveOnly: 'केवल सक्रिय',
+  subagentActiveOnlyDesc: 'पूर्ण या निष्क्रिय सबएजेंट छिपाएँ',
   subagentModeOneShot: 'एक-बार',
   subagentModeContinuable: 'जारी रखने योग्य',
   subagentCount: '{count} सबएजेंट',
diff --git a/src/client/locales-id.ts b/src/client/locales-id.ts
index 881007fe1..e6fbecba5 100644
--- a/src/client/locales-id.ts
+++ b/src/client/locales-id.ts
@@ -272,6 +272,8 @@ export const id: Record<string, string> = {
   subagentEmptyDesc: 'Subagen yang dibangkitkan di bawah agen utama akan muncul di sini',
   subagentRunning: 'Berjalan',
   subagentInactive: 'Menganggur',
+  subagentActiveOnly: 'Hanya aktif',
+  subagentActiveOnlyDesc: 'Sembunyikan subagen yang selesai atau tidak aktif',
   subagentModeOneShot: 'Sekali pakai',
   subagentModeContinuable: 'Dapat dilanjutkan',
   subagentCount: '{count} subagen',
diff --git a/src/client/locales-it.ts b/src/client/locales-it.ts
index 32f23072a..9a78d36fb 100644
--- a/src/client/locales-it.ts
+++ b/src/client/locales-it.ts
@@ -265,6 +265,8 @@ export const it: Record<string, string> = {
   subagentEmptyDesc: 'I sottoagenti generati dall’agente principale compariranno qui',
   subagentRunning: 'In esecuzione',
   subagentInactive: 'Inattivo',
+  subagentActiveOnly: 'Solo attivi',
+  subagentActiveOnlyDesc: 'Nascondi i sottoagenti completati o inattivi',
   subagentModeOneShot: 'Monouso',
   subagentModeContinuable: 'Proseguibile',
   subagentCount: '{count} sottoagenti',
diff --git a/src/client/locales-ja.ts b/src/client/locales-ja.ts
index 8d23175eb..40685ae6b 100644
--- a/src/client/locales-ja.ts
+++ b/src/client/locales-ja.ts
@@ -274,6 +274,8 @@ export const ja: Record<string, string> = {
   subagentEmptyDesc: 'メインエージェントが派生したサブエージェントはここに表示されます',
   subagentRunning: '実行中',
   subagentInactive: 'アイドル',
+  subagentActiveOnly: 'アクティブのみ',
+  subagentActiveOnlyDesc: '完了または非アクティブなサブエージェントを非表示',
   subagentModeOneShot: 'ワンショット',
   subagentModeContinuable: '継続可',
   subagentCount: '{count} 個のサブエージェント',
diff --git a/src/client/locales-ko.ts b/src/client/locales-ko.ts
index 1da475843..d4ebb3e0e 100644
--- a/src/client/locales-ko.ts
+++ b/src/client/locales-ko.ts
@@ -266,6 +266,8 @@ export const ko: Record<string, string> = {
   subagentEmptyDesc: '현재 주 에이전트에서 파생된 서브 에이전트가 여기에 표시됩니다',
   subagentRunning: '실행 중',
   subagentInactive: '대기 중',
+  subagentActiveOnly: '활성만',
+  subagentActiveOnlyDesc: '완료되었거나 비활성 상태인 서브 에이전트 숨기기',
   subagentModeOneShot: '일회성',
   subagentModeContinuable: '이어서 가능',
   subagentCount: '서브 에이전트 {count}개',
diff --git a/src/client/locales-nl.ts b/src/client/locales-nl.ts
index 7abd68f5f..81f3578af 100644
--- a/src/client/locales-nl.ts
+++ b/src/client/locales-nl.ts
@@ -272,6 +272,8 @@ export const nl: Record<string, string> = {
   subagentEmptyDesc: 'Subagents voortgebracht door de hoofdagent verschijnen hier',
   subagentRunning: 'Actief',
   subagentInactive: 'Inactief',
+  subagentActiveOnly: 'Alleen actieve',
+  subagentActiveOnlyDesc: 'Voltooide of inactieve subagents verbergen',
   subagentModeOneShot: 'One-shot',
   subagentModeContinuable: 'Vervolgbaar',
   subagentCount: '{count} subagents',
diff --git a/src/client/locales-pl.ts b/src/client/locales-pl.ts
index a061597b5..92caf8b21 100644
--- a/src/client/locales-pl.ts
+++ b/src/client/locales-pl.ts
@@ -276,6 +276,8 @@ export const pl: Record<string, string> = {
   subagentEmptyDesc: 'Podagenci powołani przez agenta głównego pojawią się tutaj',
   subagentRunning: 'Działa',
   subagentInactive: 'Bezczynny',
+  subagentActiveOnly: 'Tylko aktywne',
+  subagentActiveOnlyDesc: 'Ukryj ukończonych lub nieaktywnych podagentów',
   subagentModeOneShot: 'Jednorazowy',
   subagentModeContinuable: 'Kontynuowalny',
   subagentCount: '{count} podagentów',
diff --git a/src/client/locales-pt.ts b/src/client/locales-pt.ts
index 558ff65c1..222568992 100644
--- a/src/client/locales-pt.ts
+++ b/src/client/locales-pt.ts
@@ -257,6 +257,8 @@ export const pt: Record<string, string> = {
   subagentEmptyDesc: 'Subagentes gerados sob o agente principal aparecerão aqui',
   subagentRunning: 'Executando',
   subagentInactive: 'Inativo',
+  subagentActiveOnly: 'Apenas ativos',
+  subagentActiveOnlyDesc: 'Ocultar subagentes concluídos ou inativos',
   subagentModeOneShot: 'De uso único',
   subagentModeContinuable: 'Continuável',
   subagentCount: '{count} subagentes',
diff --git a/src/client/locales-ru.ts b/src/client/locales-ru.ts
index ff46c1f3f..506a2b419 100644
--- a/src/client/locales-ru.ts
+++ b/src/client/locales-ru.ts
@@ -272,6 +272,8 @@ export const ru: Record<string, string> = {
   subagentEmptyDesc: 'Субагенты, порождённые главным агентом, появятся здесь',
   subagentRunning: 'Выполняется',
   subagentInactive: 'Простаивает',
+  subagentActiveOnly: 'Только активные',
+  subagentActiveOnlyDesc: 'Скрыть завершённых или неактивных субагентов',
   subagentModeOneShot: 'Одноразовый',
   subagentModeContinuable: 'Продолжаемый',
   subagentCount: '{count} субагентов',
diff --git a/src/client/locales-sv.ts b/src/client/locales-sv.ts
index 276ab6401..bad259482 100644
--- a/src/client/locales-sv.ts
+++ b/src/client/locales-sv.ts
@@ -257,6 +257,8 @@ export const sv: Record<string, string> = {
   subagentEmptyDesc: 'Subagenter skapade under huvudagenten visas här',
   subagentRunning: 'Kör',
   subagentInactive: 'Inaktiv',
+  subagentActiveOnly: 'Endast aktiva',
+  subagentActiveOnlyDesc: 'Dölj slutförda eller inaktiva subagenter',
   subagentModeOneShot: 'Engångs',
   subagentModeContinuable: 'Fortsättbar',
   subagentCount: '{count} subagenter',
diff --git a/src/client/locales-th.ts b/src/client/locales-th.ts
index 6146ff8c6..6c0829a2e 100644
--- a/src/client/locales-th.ts
+++ b/src/client/locales-th.ts
@@ -274,6 +274,8 @@ export const th: Record<string, string> = {
   subagentEmptyDesc: 'ตัวแทนย่อยที่สร้างภายใต้ตัวแทนหลักจะปรากฏที่นี่',
   subagentRunning: 'กำลังทำงาน',
   subagentInactive: 'ไม่ได้ทำงาน',
+  subagentActiveOnly: 'เฉพาะที่กำลังทำงาน',
+  subagentActiveOnlyDesc: 'ซ่อนตัวแทนย่อยที่เสร็จสิ้นหรือไม่ได้ทำงาน',
   subagentModeOneShot: 'ครั้งเดียว',
   subagentModeContinuable: 'ทำต่อได้',
   subagentCount: '{count} ตัวแทนย่อย',
diff --git a/src/client/locales-tr.ts b/src/client/locales-tr.ts
index 7088ba739..dd570c60b 100644
--- a/src/client/locales-tr.ts
+++ b/src/client/locales-tr.ts
@@ -274,6 +274,8 @@ export const tr: Record<string, string> = {
   subagentEmptyDesc: 'Ana aracının altında doğan alt aracılar burada görünür',
   subagentRunning: 'Çalışıyor',
   subagentInactive: 'Etkin değil',
+  subagentActiveOnly: 'Yalnızca aktif',
+  subagentActiveOnlyDesc: 'Tamamlanan veya etkin olmayan alt aracıları gizle',
   subagentModeOneShot: 'Tek seferlik',
   subagentModeContinuable: 'Sürdürülebilir',
   subagentCount: '{count} alt aracı',
diff --git a/src/client/locales-vi.ts b/src/client/locales-vi.ts
index 5fe4559b4..7362f0907 100644
--- a/src/client/locales-vi.ts
+++ b/src/client/locales-vi.ts
@@ -274,6 +274,8 @@ export const vi: Record<string, string> = {
   subagentEmptyDesc: 'Tác nhân con do tác nhân chính tạo ra sẽ hiển thị ở đây',
   subagentRunning: 'Đang chạy',
   subagentInactive: 'Nghỉ',
+  subagentActiveOnly: 'Chỉ đang hoạt động',
+  subagentActiveOnlyDesc: 'Ẩn các tác nhân con đã hoàn tất hoặc không hoạt động',
   subagentModeOneShot: 'Một lần',
   subagentModeContinuable: 'Có thể tiếp tục',
   subagentCount: '{count} tác nhân con',
diff --git a/src/client/locales-zh-HK.ts b/src/client/locales-zh-HK.ts
index 2c2f4acc5..2a39f930c 100644
--- a/src/client/locales-zh-HK.ts
+++ b/src/client/locales-zh-HK.ts
@@ -289,6 +289,8 @@ export const zhHK: Record<string, string> = {
   subagentEmptyDesc: '目前主代理派生的子代理將顯示在這裡',
   subagentRunning: '執行中',
   subagentInactive: '閒置',
+  subagentActiveOnly: '僅顯示活躍',
+  subagentActiveOnlyDesc: '隱藏已完成或非活躍的子代理',
   subagentModeOneShot: '一次性',
   subagentModeContinuable: '可續接',
   subagentCount: '{count} 個子代理',
diff --git a/src/client/locales-zh-MO.ts b/src/client/locales-zh-MO.ts
index e6e9d0e3c..fcf22f12b 100644
--- a/src/client/locales-zh-MO.ts
+++ b/src/client/locales-zh-MO.ts
@@ -289,6 +289,8 @@ export const zhMO: Record<string, string> = {
   subagentEmptyDesc: '目前主代理派生的子代理將顯示在這裡',
   subagentRunning: '執行中',
   subagentInactive: '閒置',
+  subagentActiveOnly: '僅顯示活躍',
+  subagentActiveOnlyDesc: '隱藏已完成或非活躍的子代理',
   subagentModeOneShot: '一次性',
   subagentModeContinuable: '可續接',
   subagentCount: '{count} 個子代理',
diff --git a/src/client/locales-zh-TW.ts b/src/client/locales-zh-TW.ts
index 5630ddbb4..36abd8416 100644
--- a/src/client/locales-zh-TW.ts
+++ b/src/client/locales-zh-TW.ts
@@ -289,6 +289,8 @@ export const zhTW: Record<string, string> = {
   subagentEmptyDesc: '目前主代理派生的子代理將顯示在這裡',
   subagentRunning: '執行中',
   subagentInactive: '閒置',
+  subagentActiveOnly: '僅顯示活躍',
+  subagentActiveOnlyDesc: '隱藏已完成或非活躍的子代理',
   subagentModeOneShot: '一次性',
   subagentModeContinuable: '可續接',
   subagentCount: '{count} 個子代理',
diff --git a/src/client/locales.ts b/src/client/locales.ts
index eff0e1e0d..bdf1e2f5d 100644
--- a/src/client/locales.ts
+++ b/src/client/locales.ts
@@ -281,6 +281,8 @@ export const zh = {
   subagentEmptyDesc: '当前主代理派生的子代理将显示在这里',
   subagentRunning: '运行中',
   subagentInactive: '空闲',
+  subagentActiveOnly: '仅活跃',
+  subagentActiveOnlyDesc: '隐藏已完成或不活跃的子代理',
   subagentModeOneShot: '一次性',
   subagentModeContinuable: '可续接',
   subagentCount: '{count} 个子代理',
@@ -618,6 +620,8 @@ export const en: Record<keyof typeof zh, string> = {
   subagentEmptyDesc: 'Subagents spawned under the main agent will appear here',
   subagentRunning: 'Running',
   subagentInactive: 'Inactive',
+  subagentActiveOnly: 'Active only',
+  subagentActiveOnlyDesc: 'Hide completed or inactive subagents',
   subagentModeOneShot: 'One-shot',
   subagentModeContinuable: 'Continuable',
   subagentCount: '{count} subagents',
diff --git a/src/client/plugin-settings.ts b/src/client/plugin-settings.ts
index db6658f2d..cf301cdc7 100644
--- a/src/client/plugin-settings.ts
+++ b/src/client/plugin-settings.ts
@@ -1,8 +1,8 @@
 /**
- * Pending-writes queue for the file tree's open-with config: pin toggles and
- * (outside the settings popup) config edits land in the sidebar prefs as
- * `pluginSettings['editor']`. Writes are serialized through one promise chain
- * so a quick burst of pin clicks can never read a stale pluginSettings map
+ * Pending-writes queue for built-in and external feature settings changed
+ * outside the settings popup (for example editor pins and the Tasks active-only
+ * switch). Writes are serialized through one promise chain so a quick burst of
+ * changes can never read stale preferences and drop an earlier update
  * and drop an earlier toggle; each write pushes the whole open map patch
  * through the revision-free settings route and adopts the returned document.
  *
@@ -11,11 +11,24 @@
  * semantics cover the uncommon overlap.)
  */
 import { api } from './api.ts'
-import { parsePrefs } from './prefs.ts'
+import { parsePrefs, type SidebarPrefs } from './prefs.ts'
 import type { SidebarStore } from './state.ts'
 
 let queue: Promise<void> = Promise.resolve()
 
+/** Persist a typed top-level sidebar preference changed outside Settings. */
+export function updateSidebarPrefs(
+  store: SidebarStore,
+  patch: Partial<SidebarPrefs>,
+): void {
+  queue = queue.then(async () => {
+    const view = await api.settingsUpdate(patch)
+    store.setPrefs(parsePrefs(view.value))
+  }).catch((error: unknown) => {
+    console.error('sidebar settings write failed', error)
+  })
+}
+
 /**
  * Merge one plugin-owned settings blob of one descriptor and persist it.
  * @param store - the sidebar store (its prefs are replaced by the write result).
@@ -38,6 +51,6 @@ export function updatePluginSettings(
   }).catch((error: unknown) => {
     // The pin stays visually unchanged (no optimistic flip) and the menu
     // keeps working — the write failure is logged, not surfaced.
-    console.error('open-with settings write failed', error)
+    console.error('plugin settings write failed', error)
   })
 }
diff --git a/src/client/prefs.ts b/src/client/prefs.ts
index fa4d4b1e8..9ed0e5cc8 100644
--- a/src/client/prefs.ts
+++ b/src/client/prefs.ts
@@ -52,6 +52,9 @@ export function parsePrefs(value: unknown): SidebarPrefs {
     autoOpenSubagent: typeof record.autoOpenSubagent === 'boolean'
       ? record.autoOpenSubagent
       : SIDEBAR_PREFS_DEFAULTS.autoOpenSubagent,
+    hideCompletedSubagents: typeof record.hideCompletedSubagents === 'boolean'
+      ? record.hideCompletedSubagents
+      : SIDEBAR_PREFS_DEFAULTS.hideCompletedSubagents,
     autoOpenJobs: typeof record.autoOpenJobs === 'boolean'
       ? record.autoOpenJobs
       : SIDEBAR_PREFS_DEFAULTS.autoOpenJobs,
diff --git a/src/client/service.ts b/src/client/service.ts
index 6d2915464..973b9d086 100644
--- a/src/client/service.ts
+++ b/src/client/service.ts
@@ -117,7 +117,8 @@ export interface SidebarSettingsDeclaration {
    * Extra settings rows rendered under the feature's own row in the
    * settings page (only while the feature is enabled). Keys must be fields
    * of the host's PrefsSchema (built-ins: 'autoOpenSubagent',
-   * 'agentTerminalTools', 'agentOpenTools', 'terminalFontFamily'); unknown
+   * 'hideCompletedSubagents', 'agentTerminalTools', 'agentOpenTools',
+   * 'terminalFontFamily'); unknown
    * keys are dropped by the settings seam.
    */
   toggles?: readonly SidebarSettingToggle[]
diff --git a/src/client/subagent-detect.ts b/src/client/subagent-detect.ts
index f45b3ad54..a210b6ce1 100644
--- a/src/client/subagent-detect.ts
+++ b/src/client/subagent-detect.ts
@@ -14,6 +14,7 @@ import type {
   SidebarSessionList,
   SidebarSessionSummary,
   SidebarSubagentCatalog,
+  SidebarSubagentChildEntry,
 } from '../context-types.ts'
 import { SIDE_LABEL_PREFIX } from '../sidechat-core.ts'
 
@@ -87,6 +88,57 @@ export function collectBranchIds(
   return out
 }
 
+/**
+ * Whether one healthy catalog entry is currently active. The catalog's
+ * sampled activity is authoritative, while the session summary is accepted
+ * as a fresher positive signal during the short interval before the catalog
+ * catches up. An inactive value never overrides a running summary.
+ */
+export function isActiveSubagent(
+  entry: SidebarSubagentChildEntry,
+  summary: SidebarSessionSummary | undefined,
+): boolean {
+  return entry.activity === 'running' || summary?.running === true
+}
+
+/**
+ * Whether a catalog child belongs in the active-only topology. An inactive
+ * ancestor remains as structural context when one of its descendants is
+ * active; cycles and not-yet-hydrated catalogs fail closed to the node's own
+ * sampled activity.
+ */
+export function hasActiveSubagentBranch(
+  entry: SidebarSubagentChildEntry,
+  catalogs: Readonly<Record<string, SidebarSubagentCatalog>>,
+  byId: Readonly<Record<string, SidebarSessionSummary>>,
+  currentSessionId?: string,
+  seen: ReadonlySet<string> = new Set(),
+): boolean {
+  if (isActiveSubagent(entry, byId[entry.id])) return true
+  // The summary lineage arrives before lazy catalogs hydrate. Use it as an
+  // immediate positive signal so active deep branches never pop in late.
+  if (countSubagentDescendants(byId, entry.id).runningCount > 0) return true
+  // Keep the selected subagent and its ancestors as navigation context even
+  // after its run settles; every unrelated inactive branch remains filtered.
+  if (currentSessionId !== undefined) {
+    const lineageSeen = new Set<string>()
+    let current = byId[currentSessionId]
+    while (current?.origin === 'subagent' && !lineageSeen.has(current.id)) {
+      lineageSeen.add(current.id)
+      if (current.id === entry.id) return true
+      current = current.parentId === undefined ? undefined : byId[current.parentId]
+    }
+  }
+  if (seen.has(entry.id)) return false
+  const nextSeen = new Set(seen)
+  nextSeen.add(entry.id)
+  return (catalogs[entry.id]?.entries ?? []).some(child => (
+    child.kind === 'child'
+      && !(child.label?.startsWith(SIDE_LABEL_PREFIX) ?? false)
+      && hasActiveSubagentBranch(child, catalogs, byId, currentSessionId, nextSeen)
+  ))
+}
+
 /**
  * Whether a new direct subagent appeared under `sessionId` between two
  * consecutive list snapshots (the count crossed 0 → >0). Switching to a
diff --git a/src/config.ts b/src/config.ts
index 160c08c67..891a71743 100644
--- a/src/config.ts
+++ b/src/config.ts
@@ -120,6 +120,7 @@ export const PrefsSchema: z<SidebarPrefs> = z.object({
   openByDefault: z.boolean().default(false),
   defaultWidthPercent: z.number().step(1).min(WIDTH_PERCENT_MIN).max(WIDTH_PERCENT_MAX).default(WIDTH_PERCENT_DEFAULT),
   autoOpenSubagent: z.boolean().default(true),
+  hideCompletedSubagents: z.boolean().default(true),
   autoOpenJobs: z.boolean().default(true),
   agentTerminalTools: z.boolean().default(false),
   agentOpenTools: z.boolean().default(false),
diff --git a/src/prefs-shared.ts b/src/prefs-shared.ts
index f7e257925..9c74bac14 100644
--- a/src/prefs-shared.ts
+++ b/src/prefs-shared.ts
@@ -20,6 +20,11 @@ export interface SidebarPrefs {
    * Subagent page when the current conversation spawns a new subagent.
    */
   autoOpenSubagent: boolean
+  /**
+   * Whether the Tasks topology hides completed/inactive subagents. On by
+   * default; the in-view switch and the Tasks card setting stay synchronized.
+   */
+  hideCompletedSubagents: boolean
   /**
    * Whether the sidebar auto-activates (opens the panel) and expands the
    * Jobs page when a NEW background job appears for the current
@@ -235,6 +240,7 @@ export const SIDEBAR_PREFS_DEFAULTS: SidebarPrefs = {
   openByDefault: false,
   defaultWidthPercent: WIDTH_PERCENT_DEFAULT,
   autoOpenSubagent: true,
+  hideCompletedSubagents: true,
   autoOpenJobs: true,
   agentTerminalTools: false,
   agentOpenTools: false,
diff --git a/tests/builtins.spec.ts b/tests/builtins.spec.ts
index e1baa8089..96f04bba8 100644
--- a/tests/builtins.spec.ts
+++ b/tests/builtins.spec.ts
@@ -80,7 +80,7 @@ describe('built-in tab registrations', () => {
   it('the subagent tab declares its auto-open related settings', () => {
     const { service } = setup()
     const toggles = service.getTab('subagent')?.settings?.toggles ?? []
-    expect(toggles.map(t => t.key)).toEqual(['autoOpenSubagent', 'autoOpenJobs'])
+    expect(toggles.map(t => t.key)).toEqual(['autoOpenSubagent', 'hideCompletedSubagents', 'autoOpenJobs'])
   })
 
   it('the editor tab declares its merged-mode (embedded file tree) setting', () => {
diff --git a/tests/plugin-shape.spec.ts b/tests/plugin-shape.spec.ts
index 992c5730a..ef5d2cfac 100644
--- a/tests/plugin-shape.spec.ts
+++ b/tests/plugin-shape.spec.ts
@@ -60,6 +60,7 @@ describe('dsh-better-sidebar plugin export shape', () => {
     expect(resolved.openByDefault).toBe(false)
     expect(resolved.defaultWidthPercent).toBe(35)
     expect(resolved.autoOpenSubagent).toBe(true)
+    expect(resolved.hideCompletedSubagents).toBe(true)
     // A new background job auto-opens the Jobs page too.
     expect(resolved.autoOpenJobs).toBe(true)
     // The terminal tools default OFF (the feature is dormant until the user
@@ -94,6 +95,6 @@ describe('dsh-better-sidebar plugin export shape', () => {
     const overridden = (PrefsSchema as unknown as {
       (input: Record<string, unknown> | undefined): Record<string, unknown>
     })({ openByDefault: false, defaultWidthPercent: 45 })
-    expect(overridden).toEqual({ openByDefault: false, defaultWidthPercent: 45, autoOpenSubagent: true, autoOpenJobs: true, agentTerminalTools: false, agentOpenTools: false, bottomPanelAutoTerminal: true, terminalFontFamily: '', terminalFontSize: 13, interceptOpenPath: true, editorExplorer: false, terminalShell: '', terminalShellArgs: '', titleBarCompat: false, titleBarStripPx: 40, htmlViewerNoSandbox: false, htmlViewerDefaultUnsafe: false, browserNoSandbox: false, browserInterceptLinks: true, browserInterceptHttp: true, browserInterceptHttps: false, tabsEnabled: {}, viewersEnabled: {}, pluginSettings: {} })
+    expect(overridden).toEqual({ openByDefault: false, defaultWidthPercent: 45, autoOpenSubagent: true, hideCompletedSubagents: true, autoOpenJobs: true, agentTerminalTools: false, agentOpenTools: false, bottomPanelAutoTerminal: true, terminalFontFamily: '', terminalFontSize: 13, interceptOpenPath: true, editorExplorer: false, terminalShell: '', terminalShellArgs: '', titleBarCompat: false, titleBarStripPx: 40, htmlViewerNoSandbox: false, htmlViewerDefaultUnsafe: false, browserNoSandbox: false, browserInterceptLinks: true, browserInterceptHttp: true, browserInterceptHttps: false, tabsEnabled: {}, viewersEnabled: {}, pluginSettings: {} })
   })
 })
diff --git a/tests/prefs.spec.ts b/tests/prefs.spec.ts
index 647b5133f..e886d8335 100644
--- a/tests/prefs.spec.ts
+++ b/tests/prefs.spec.ts
@@ -36,6 +36,7 @@ describe('side card preferences', () => {
         openByDefault: false,
         defaultWidthPercent: 60,
         autoOpenSubagent: false,
+        hideCompletedSubagents: true,
         autoOpenJobs: true,
         agentTerminalTools: true, agentOpenTools: false,
         bottomPanelAutoTerminal: true,
@@ -68,6 +69,7 @@ describe('side card preferences', () => {
         openByDefault: false,
         defaultWidthPercent: 33,
         autoOpenSubagent: true,
+        hideCompletedSubagents: true,
         autoOpenJobs: true,
         agentTerminalTools: false, agentOpenTools: false,
         bottomPanelAutoTerminal: true,
@@ -100,6 +102,7 @@ describe('side card preferences', () => {
         openByDefault: false,
         defaultWidthPercent: 40,
         autoOpenSubagent: true,
+        hideCompletedSubagents: true,
         autoOpenJobs: true,
         agentTerminalTools: false, agentOpenTools: false,
         bottomPanelAutoTerminal: true,
@@ -267,9 +270,9 @@ describe('side card preferences', () => {
     const store = createSidebarStore()
     // Node environment: no window → the width falls back to PANEL_DEFAULT,
     // while the open flag still follows the preference.
-    store.setPrefs({ openByDefault: false, defaultWidthPercent: 45, autoOpenSubagent: true, autoOpenJobs: true, agentTerminalTools: false, agentOpenTools: false, bottomPanelAutoTerminal: true, terminalFontFamily: '', terminalFontSize: 13, interceptOpenPath: true, editorExplorer: true, terminalShell: '', terminalShellArgs: '', titleBarScheme: 'auto', titleBarPresetId: '', customCss: '', titleBarCompat: false, titleBarStripPx: 40, htmlViewerNoSandbox: false, htmlViewerDefaultUnsafe: false, browserNoSandbox: false, browserInterceptLinks: true, browserInterceptHttp: true, browserInterceptHttps: false, tabsEnabled: {}, viewersEnabled: {}, pluginSettings: {} })
+    store.setPrefs({ openByDefault: false, defaultWidthPercent: 45, autoOpenSubagent: true, hideCompletedSubagents: true, autoOpenJobs: true, agentTerminalTools: false, agentOpenTools: false, bottomPanelAutoTerminal: true, terminalFontFamily: '', terminalFontSize: 13, interceptOpenPath: true, editorExplorer: true, terminalShell: '', terminalShellArgs: '', titleBarScheme: 'auto', titleBarPresetId: '', customCss: '', titleBarCompat: false, titleBarStripPx: 40, htmlViewerNoSandbox: false, htmlViewerDefaultUnsafe: false, browserNoSandbox: false, browserInterceptLinks: true, browserInterceptHttp: true, browserInterceptHttps: false, tabsEnabled: {}, viewersEnabled: {}, pluginSettings: {} })
     store.setSession('fresh-session')
-    expect(store.getPrefs()).toEqual({ openByDefault: false, defaultWidthPercent: 45, autoOpenSubagent: true, autoOpenJobs: true, agentTerminalTools: false, agentOpenTools: false, bottomPanelAutoTerminal: true, terminalFontFamily: '', terminalFontSize: 13, interceptOpenPath: true, editorExplorer: true, terminalShell: '', terminalShellArgs: '', titleBarScheme: 'auto', titleBarPresetId: '', customCss: '', titleBarCompat: false, titleBarStripPx: 40, htmlViewerNoSandbox: false, htmlViewerDefaultUnsafe: false, browserNoSandbox: false, browserInterceptLinks: true, browserInterceptHttp: true, browserInterceptHttps: false, tabsEnabled: {}, viewersEnabled: {}, pluginSettings: {} })
+    expect(store.getPrefs()).toEqual({ openByDefault: false, defaultWidthPercent: 45, autoOpenSubagent: true, hideCompletedSubagents: true, autoOpenJobs: true, agentTerminalTools: false, agentOpenTools: false, bottomPanelAutoTerminal: true, terminalFontFamily: '', terminalFontSize: 13, interceptOpenPath: true, editorExplorer: true, terminalShell: '', terminalShellArgs: '', titleBarScheme: 'auto', titleBarPresetId: '', customCss: '', titleBarCompat: false, titleBarStripPx: 40, htmlViewerNoSandbox: false, htmlViewerDefaultUnsafe: false, browserNoSandbox: false, browserInterceptLinks: true, browserInterceptHttp: true, browserInterceptHttps: false, tabsEnabled: {}, viewersEnabled: {}, pluginSettings: {} })
     const snapshot = store.getSnapshot()
     expect(snapshot.sessionId).toBe('fresh-session')
     expect(snapshot.state?.panelOpen).toBe(false)
@@ -305,7 +308,7 @@ describe('side card preferences', () => {
 
   it('skips the default seed tab when the editor (files window) type is disabled', () => {
     const store = createSidebarStore()
-    store.setPrefs({ openByDefault: true, defaultWidthPercent: 30, autoOpenSubagent: true, autoOpenJobs: true, agentTerminalTools: false, agentOpenTools: false, bottomPanelAutoTerminal: true, terminalFontFamily: '', terminalFontSize: 13, interceptOpenPath: true, editorExplorer: true, terminalShell: '', terminalShellArgs: '', titleBarScheme: 'auto', titleBarPresetId: '', customCss: '', titleBarCompat: false, titleBarStripPx: 40, htmlViewerNoSandbox: false, htmlViewerDefaultUnsafe: false, browserNoSandbox: false, browserInterceptLinks: true, browserInterceptHttp: true, browserInterceptHttps: false, tabsEnabled: { editor: false }, viewersEnabled: {}, pluginSettings: {} })
+    store.setPrefs({ openByDefault: true, defaultWidthPercent: 30, autoOpenSubagent: true, hideCompletedSubagents: true, autoOpenJobs: true, agentTerminalTools: false, agentOpenTools: false, bottomPanelAutoTerminal: true, terminalFontFamily: '', terminalFontSize: 13, interceptOpenPath: true, editorExplorer: true, terminalShell: '', terminalShellArgs: '', titleBarScheme: 'auto', titleBarPresetId: '', customCss: '', titleBarCompat: false, titleBarStripPx: 40, htmlViewerNoSandbox: false, htmlViewerDefaultUnsafe: false, browserNoSandbox: false, browserInterceptLinks: true, browserInterceptHttp: true, browserInterceptHttps: false, tabsEnabled: { editor: false }, viewersEnabled: {}, pluginSettings: {} })
     store.setSession('no-editor')
     const state = store.getSnapshot().state!
     const tabs = allLeaves(state.splits).flatMap(leaf => leaf.tabs)
@@ -315,7 +318,7 @@ describe('side card preferences', () => {
     // editorExplorer modes.
     for (const editorExplorer of [true, false]) {
       const openStore = createSidebarStore()
-      openStore.setPrefs({ openByDefault: true, defaultWidthPercent: 30, autoOpenSubagent: true, autoOpenJobs: true, agentTerminalTools: false, agentOpenTools: false, bottomPanelAutoTerminal: true, terminalFontFamily: '', terminalFontSize: 13, interceptOpenPath: true, editorExplorer, terminalShell: '', terminalShellArgs: '', titleBarScheme: 'auto', titleBarPresetId: '', customCss: '', titleBarCompat: false, titleBarStripPx: 40, htmlViewerNoSandbox: false, htmlViewerDefaultUnsafe: false, browserNoSandbox: false, browserInterceptLinks: true, browserInterceptHttp: true, browserInterceptHttps: false, tabsEnabled: {}, viewersEnabled: {}, pluginSettings: {} })
+      openStore.setPrefs({ openByDefault: true, defaultWidthPercent: 30, autoOpenSubagent: true, hideCompletedSubagents: true, autoOpenJobs: true, agentTerminalTools: false, agentOpenTools: false, bottomPanelAutoTerminal: true, terminalFontFamily: '', terminalFontSize: 13, interceptOpenPath: true, editorExplorer, terminalShell: '', terminalShellArgs: '', titleBarScheme: 'auto', titleBarPresetId: '', customCss: '', titleBarCompat: false, titleBarStripPx: 40, htmlViewerNoSandbox: false, htmlViewerDefaultUnsafe: false, browserNoSandbox: false, browserInterceptLinks: true, browserInterceptHttp: true, browserInterceptHttps: false, tabsEnabled: {}, viewersEnabled: {}, pluginSettings: {} })
       openStore.setSession(`with-editor-${editorExplorer}`)
       const openTabs = allLeaves(openStore.getSnapshot().state!.splits).flatMap(leaf => leaf.tabs)
       expect(openTabs.map(tab => tab.type)).toEqual(['editor'])
@@ -325,7 +328,7 @@ describe('side card preferences', () => {
   it('seeds the empty editor home tab (files window) in both editorExplorer modes', () => {
     for (const editorExplorer of [true, false]) {
       const store = createSidebarStore()
-      store.setPrefs({ openByDefault: true, defaultWidthPercent: 30, autoOpenSubagent: true, autoOpenJobs: true, agentTerminalTools: false, agentOpenTools: false, bottomPanelAutoTerminal: true, terminalFontFamily: '', terminalFontSize: 13, interceptOpenPath: true, editorExplorer, terminalShell: '', terminalShellArgs: '', titleBarScheme: 'auto', titleBarPresetId: '', customCss: '', titleBarCompat: false, titleBarStripPx: 40, htmlViewerNoSandbox: false, htmlViewerDefaultUnsafe: false, browserNoSandbox: false, browserInterceptLinks: true, browserInterceptHttp: true, browserInterceptHttps: false, tabsEnabled: {}, viewersEnabled: {}, pluginSettings: {} })
+      store.setPrefs({ openByDefault: true, defaultWidthPercent: 30, autoOpenSubagent: true, hideCompletedSubagents: true, autoOpenJobs: true, agentTerminalTools: false, agentOpenTools: false, bottomPanelAutoTerminal: true, terminalFontFamily: '', terminalFontSize: 13, interceptOpenPath: true, editorExplorer, terminalShell: '', terminalShellArgs: '', titleBarScheme: 'auto', titleBarPresetId: '', customCss: '', titleBarCompat: false, titleBarStripPx: 40, htmlViewerNoSandbox: false, htmlViewerDefaultUnsafe: false, browserNoSandbox: false, browserInterceptLinks: true, browserInterceptHttp: true, browserInterceptHttps: false, tabsEnabled: {}, viewersEnabled: {}, pluginSettings: {} })
       store.setSession(`fresh-${editorExplorer}`)
       const tabs = allLeaves(store.getSnapshot().state!.splits).flatMap(leaf => leaf.tabs)
       expect(tabs).toHaveLength(1)
diff --git a/tests/smoke.spec.ts b/tests/smoke.spec.ts
index 6eef4d46a..56e856906 100644
--- a/tests/smoke.spec.ts
+++ b/tests/smoke.spec.ts
@@ -838,6 +838,7 @@ describe('side card settings routes', () => {
         openByDefault: false,
         defaultWidthPercent: 35,
         autoOpenSubagent: true,
+        hideCompletedSubagents: true,
         autoOpenJobs: true,
         agentTerminalTools: false, agentOpenTools: false,
         bottomPanelAutoTerminal: true,
diff --git a/tests/subagent-active-filter.spec.tsx b/tests/subagent-active-filter.spec.tsx
new file mode 100644
index 000000000..9ce2d328f
--- /dev/null
+++ b/tests/subagent-active-filter.spec.tsx
@@ -0,0 +1,199 @@
+/**
+ * Tasks active-only filter: enabled by default, settled rows stay out of the
+ * tree, live descendant branches retain their ancestor context, and the
+ * in-view switch restores the complete topology immediately.
+ */
+// @vitest-environment jsdom
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
+import { createElement, type ReactNode } from 'react'
+import { createRoot, type Root } from 'react-dom/client'
+import { act } from 'react-dom/test-utils'
+import { SubagentView } from '../src/client/SubagentView.tsx'
+import { api } from '../src/client/api.ts'
+import type { SidebarStore } from '../src/client/state.ts'
+import { SIDEBAR_PREFS_DEFAULTS } from '../src/prefs-shared.ts'
+import type { Context, SidebarSessionList } from '../src/context-types.ts'
+
+function makeStore(initial: SidebarSessionList) {
+  let snapshot = initial
+  const listeners = new Set<() => void>()
+  return {
+    getSnapshot: () => snapshot,
+    subscribe: (listener: () => void) => {
+      listeners.add(listener)
+      return () => { listeners.delete(listener) }
+    },
+  }
+}
+
+function makeCtx(list: ReturnType<typeof makeStore>): Context {
+  return {
+    sessions: {
+      list,
+      setSubagentCatalogOpen: () => {},
+      openSubagent: () => {},
+      open: () => {},
+      refreshSubagents: async () => {},
+    },
+  } as unknown as Context
+}
+
+function snapshot(): SidebarSessionList {
+  const catalog = (entries: NonNullable<SidebarSessionList['subagentsByParent']>[string]['entries']) => ({
+    entries,
+    parentAvailable: true,
+    state: 'ready' as const,
+    error: null,
+  })
+  const child = (id: string, activity: 'running' | 'inactive', hasChildren = false) => ({
+    kind: 'child' as const,
+    id,
+    activity,
+    hasChildren,
+    mode: 'one-shot' as const,
+  })
+  return {
+    current: 'root',
+    byId: {
+      root: { id: 'root', displayTitle: 'Main', running: true },
+      active: { id: 'active', displayTitle: 'Active child', origin: 'subagent', parentId: 'root', running: true },
+      done: { id: 'done', displayTitle: 'Completed child', origin: 'subagent', parentId: 'root', running: false },
+      ancestor: { id: 'ancestor', displayTitle: 'Ancestor context', origin: 'subagent', parentId: 'root', running: false },
+      nested: { id: 'nested', displayTitle: 'Nested active', origin: 'subagent', parentId: 'ancestor', running: true },
+    },
+    subagentsByParent: {
+      root: catalog([
+        child('active', 'running'),
+        child('done', 'inactive'),
+        child('ancestor', 'inactive', true),
+      ]),
+      ancestor: catalog([child('nested', 'running')]),
+    },
+    jobsBySession: {},
+  }
+}
+
+function mount(node: ReactNode): { container: HTMLDivElement; unmount: () => void } {
+  const container = document.createElement('div')
+  document.body.append(container)
+  const root: Root = createRoot(container)
+  act(() => { root.render(node) })
+  return {
+    container,
+    unmount: () => {
+      act(() => { root.unmount() })
+      container.remove()
+    },
+  }
+}
+
+beforeEach(() => {
+  Object.defineProperty(globalThis.navigator, 'language', { value: 'en-US', configurable: true })
+})
+
+afterEach(() => {
+  vi.restoreAllMocks()
+  for (const element of document.querySelectorAll('body > div')) element.remove()
+})
+
+describe('SubagentView active-only filter', () => {
+  it('defaults on and hides completed subagents while preserving active branches', () => {
+    const list = makeStore(snapshot())
+    const { container, unmount } = mount(
+      createElement(SubagentView, { sessionId: 'root', active: false, ctx: makeCtx(list) }),
+    )
+
+    const toggle = container.querySelector('button[role="switch"]') as HTMLButtonElement
+    expect(toggle).not.toBeNull()
+    expect(toggle.getAttribute('aria-checked')).toBe('true')
+    expect(toggle.textContent).toContain('Active only')
+    expect(container.textContent).toContain('Active child')
+    expect(container.textContent).toContain('Nested active')
+    expect(container.textContent).toContain('Ancestor context')
+    expect(container.textContent).not.toContain('Completed child')
+    unmount()
+  })
+
+  it('explains an empty filtered result instead of rendering a blank tree', () => {
+    const settled = snapshot()
+    settled.byId.active!.running = false
+    settled.byId.nested!.running = false
+    const rootEntries = settled.subagentsByParent!.root!.entries
+    for (const entry of rootEntries) if (entry.kind === 'child') entry.activity = 'inactive'
+    const nestedEntries = settled.subagentsByParent!.ancestor!.entries
+    for (const entry of nestedEntries) if (entry.kind === 'child') entry.activity = 'inactive'
+    const list = makeStore(settled)
+    const { container, unmount } = mount(
+      createElement(SubagentView, { sessionId: 'root', active: false, ctx: makeCtx(list) }),
+    )
+
+    expect(container.textContent).not.toContain('Completed child')
+    expect(container.textContent).toContain('Hide completed or inactive subagents')
+    expect(container.textContent).toContain('4 subagents')
+    unmount()
+  })
+
+  it('keeps the selected inactive subagent visible as navigation context', () => {
+    const selected = snapshot()
+    selected.current = 'done'
+    const list = makeStore(selected)
+    const { container, unmount } = mount(
+      createElement(SubagentView, { sessionId: 'done', active: false, ctx: makeCtx(list) }),
+    )
+
+    const row = Array.from(container.querySelectorAll('[role="treeitem"]')).find(
+      element => element.textContent?.includes('Completed child') ?? false,
+    )
+    expect(row?.getAttribute('aria-current')).toBe('true')
+    unmount()
+  })
+
+  it('honors a persisted opt-out from the shared sidebar settings', () => {
+    const list = makeStore(snapshot())
+    const sidebarStore = {
+      getPrefs: () => ({
+        ...SIDEBAR_PREFS_DEFAULTS,
+        hideCompletedSubagents: false,
+      }),
+      subscribe: () => () => {},
+    } as unknown as SidebarStore
+    const { container, unmount } = mount(
+      createElement(SubagentView, {
+        sessionId: 'root', active: false, ctx: makeCtx(list), store: sidebarStore,
+      }),
+    )
+
+    expect(container.querySelector('button[role="switch"]')?.getAttribute('aria-checked')).toBe('false')
+    expect(container.textContent).toContain('Completed child')
+    unmount()
+  })
+
+  it('reveals completed subagents and persists the switch through shared settings', async () => {
+    const list = makeStore(snapshot())
+    const prefs = { ...SIDEBAR_PREFS_DEFAULTS }
+    const setPrefs = vi.fn()
+    const sidebarStore = {
+      getPrefs: () => prefs,
+      setPrefs,
+      subscribe: () => () => {},
+    } as unknown as SidebarStore
+    const update = vi.spyOn(api, 'settingsUpdate').mockResolvedValue({
+      value: { ...prefs, hideCompletedSubagents: false },
+    })
+    const { container, unmount } = mount(
+      createElement(SubagentView, {
+        sessionId: 'root', active: false, ctx: makeCtx(list), store: sidebarStore,
+      }),
+    )
+
+    const toggle = container.querySelector('button[role="switch"]') as HTMLButtonElement
+    await act(async () => { toggle.click() })
+    expect(toggle.getAttribute('aria-checked')).toBe('false')
+    expect(container.textContent).toContain('Completed child')
+    await vi.waitFor(() => {
+      expect(update).toHaveBeenCalledWith({ hideCompletedSubagents: false })
+      expect(setPrefs).toHaveBeenCalledWith(expect.objectContaining({ hideCompletedSubagents: false }))
+    })
+    unmount()
+  })
+})
diff --git a/tests/subagent-detect.spec.ts b/tests/subagent-detect.spec.ts
index 2fe4e069b..feb2f93c1 100644
--- a/tests/subagent-detect.spec.ts
+++ b/tests/subagent-detect.spec.ts
@@ -1,7 +1,7 @@
 import { describe, expect, it } from 'vitest'
 import {
   collectBranchIds, countSubagentDescendants, detectNewDirectSubagent,
-  directSubagentCount, rootAncestor,
+  directSubagentCount, hasActiveSubagentBranch, isActiveSubagent, rootAncestor,
 } from '../src/client/subagent-detect.ts'
 import type { SidebarSessionList, SidebarSubagentCatalog } from '../src/context-types.ts'
 
@@ -142,6 +142,54 @@ describe('subagent detection over the sessions list feed', () => {
     expect(rootAncestor(byId, undefined)).toBeUndefined()
   })
 
+  it('recognizes active rows and preserves inactive ancestors of active descendants', () => {
+    const child = (
+      id: string,
+      activity: 'running' | 'inactive',
+      hasChildren = false,
+    ): Extract<SidebarSubagentCatalog['entries'][number], { kind: 'child' }> => ({
+      kind: 'child', id, activity, hasChildren, mode: 'one-shot',
+    })
+    const byId: SidebarSessionList['byId'] = {
+      root: { id: 'root', displayTitle: 'Root' },
+      staleCatalog: { id: 'staleCatalog', displayTitle: 'Fresh summary', running: true },
+      ancestor: { id: 'ancestor', displayTitle: 'Ancestor', origin: 'subagent', parentId: 'root' },
+      deepLive: { id: 'deepLive', displayTitle: 'Deep live', origin: 'subagent', parentId: 'ancestor', running: true },
+      selectedDone: { id: 'selectedDone', displayTitle: 'Selected done', origin: 'subagent', parentId: 'ancestor' },
+    }
+    expect(isActiveSubagent(child('live', 'running'), undefined)).toBe(true)
+    expect(isActiveSubagent(child('staleCatalog', 'inactive'), byId.staleCatalog)).toBe(true)
+    expect(isActiveSubagent(child('done', 'inactive'), undefined)).toBe(false)
+
+    const ancestor = child('ancestor', 'inactive', true)
+    // Summary lineage preserves the branch before its lazy catalog hydrates.
+    expect(hasActiveSubagentBranch(ancestor, {}, byId)).toBe(true)
+    expect(hasActiveSubagentBranch(
+      child('selectedDone', 'inactive'), {}, byId, 'selectedDone',
+    )).toBe(true)
+    byId.deepLive!.running = false
+    const catalogs: Record<string, SidebarSubagentCatalog> = {
+      ancestor: {
+        entries: [child('deep-live', 'running')],
+        parentAvailable: true,
+        state: 'ready',
+        error: null,
+      },
+    }
+    expect(hasActiveSubagentBranch(ancestor, catalogs, byId)).toBe(true)
+    expect(hasActiveSubagentBranch(child('done', 'inactive'), catalogs, byId)).toBe(false)
+
+    // Side Chat descendants never keep an otherwise-settled Tasks branch.
+    catalogs.ancestor!.entries = [{ ...child('side', 'running'), label: 'Side: hidden thread' }]
+    expect(hasActiveSubagentBranch(ancestor, catalogs, byId)).toBe(false)
+    // Malformed cyclic catalogs terminate without inventing activity.
+    catalogs.ancestor!.entries = [child('loop', 'inactive', true)]
+    catalogs.loop = {
+      entries: [ancestor], parentAvailable: true, state: 'ready', error: null,
+    }
+    expect(hasActiveSubagentBranch(ancestor, catalogs, byId)).toBe(false)
+  })
+
   it('collects every catalog branch of the topology, cycle-safe', () => {
     const child = (id: string, hasChildren: boolean): SidebarSubagentCatalog['entries'][number] => ({
       kind: 'child', id, activity: 'inactive', hasChildren, mode: 'one-shot',