diff --git a/AGENTS.md b/AGENTS.md
index 1911f09..a4b552b 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -606,8 +606,15 @@ interface OpenTabSeed {
 - **面板表面**：右/底面板背景 = `var(--dsw-alias-bg-layer-1)`（通用卡片表面）。**绝不消费 `--dsw-specific-sidebar-fill`**——那是宿主左侧导航列专属令牌，皮肤系统按左导航语义覆盖它（dsh-web-ui 皮肤把它做成半透明玻璃或主题色，Aqua 设成 `transparent`），面板消费它会失去填充或与标签令牌冲突。皮肤要整体换面板表面：覆写 `--dsw-alias-bg-layer-1` 即可（dsh-web-ui 10 款皮肤都已覆盖，无需任何额外工作）。
 - **终端/编辑器表面**：经 `effectiveTokenValue` 读取 `--dsw-alias-bg-base`——`transparent` 与 alpha < 0.9 的半透明玻璃值（dsh-web-ui 皮肤用 rgba 0.16–0.7）一律回退不透明底色，文字永不叠在皮肤背景画上滚动（issue #90）；≥ 0.9 的近不透明值（如皮肤作用域内 0.96 的瓷器玻璃）放行，皮肤仍能控制终端表面。
 - **根锚点**：宿主 div 带 `data-dsh-better-sidebar` 属性（append 到 `document.body`）。其内是**统一面板宿主层** `[data-dsh-panel-host]`（`position:fixed; inset:0; z-index:40; pointer-events:none`，v0.13.1+）：面板/开关簇在其内 **absolute** 定位（层 inset:0 即视口坐标），免疫桌面套壳中间层 transform 对 fixed 含块的劫持；页面级 transform（罕见）触发 `data-dsh-panel-host-degraded` 降级同步。皮肤若要做作用域覆盖（deep-whale 的做法），限定在 `[data-dsh-better-sidebar]` 内即可，避免全局改写影响宿主。
-- **布局变量**（写在 `<html>` 上，面板打开时有效）：`--dsh-sidebar-width` / `--dsh-sidebar-height`（面板几何；拖拽期间逐帧更新）。宿主推挤 = `#root` 的 `margin-right/width: calc(100% - var)`（v0.13.1+ 防桌面壳加性溢出）与 centerCol 的 `margin-bottom`；推挤锚点是 **`#root [data-dsh-frame] > [data-pane="conversation"]`**（稳定 data 属性，**禁止**退回 `nth-child` 位置锚定）。
-- **桌面信号**（v0.13.1+）：DSH Desktop 壳在 URL 注入 `dsh-desktop-mode` / `dsh-desktop-platform`（preload 另暴露 `__DSH_DESKTOP_FILE_PATH__`）；win32 `advanced` 壳右上角有 32px 窗口控制 overlay，插件自动启用标题栏兼容（`body[data-dsh-title-bar-compat]` + `--dsh-title-bar-strip: 32px`），手动 pref 可覆盖；`compatibility` 模式与无信号环境不避让。
+- **布局变量**（写在 `<html>` 上，面板打开时有效）：`--dsh-sidebar-width` / `--dsh-sidebar-height`（面板几何；拖拽期间逐帧更新）。宿主推挤 = `#root` 的 `margin-right/width: calc(100% - var)`（v0.13.1+ 防桌面壳加性溢出）与 centerCol 的 `margin-bottom`；推挤锚点是**复合选择器**（同一元素双保险，禁止退回 `nth-child` 位置锚定）：`#root [data-dsh-frame] > [data-pane="conversation"]` **与** `#root :has(> [data-slot="conversation"])`（0.1.x 命名 / rc.8 时代命名，live 页面实测同元素；`drag-layout.e2e.ts` 断言两者同元素）。
+- **桌面信号与标题栏兼容**（v0.14.1+ 四选项模型，取代旧"win32 advanced 自动 32px"硬编码）：
+  - 壳信号（只读报告，不自动触发任何修改）：URL `dsh-desktop-mode` / `dsh-desktop-platform`（DSH Desktop 壳注入；preload 另暴露 `__DSH_DESKTOP_FILE_PATH__`）；可选契约参数 `dsh-desktop-titlebar-inset`（壳声明自己预留的顶栏像素，0–120，clamp；`parseDesktopEnv().titlebarInset`）。
+  - **strip 取值链**（`src/client/titlebar-strip.ts` 唯一决策点，纯函数）：⓪ `web` 方案强制 0（显式 DSH官方Web，连 WCO 也不适用）；① `navigator.windowControlsOverlay` 标准 API 真实几何（`src/client/wco.ts`，反应式订阅 `geometrychange`，最大化/还原实时更新——**即使为 0 也权威**，`visible=false` 的幽灵 API 视为缺失，覆盖 #257 的 32/36px 差异）；② URL `dsh-desktop-titlebar-inset`；③ 壳预设 `stripFor`（仅 `preset` 方案）；④ 手动 `titleBarStripPx`（仅 `custom` 方案）；⑤ 0（网页零修改）。结果驱动 `body[data-dsh-title-bar-compat]` + `--dsh-title-bar-strip`（语义与旧布尔一致）。
+  - **四选项设置**（`SidebarPrefs.titleBarScheme`，设置页主行**下拉**：`auto` 默认 / `web` / `preset` / `custom`）：`auto` = 只信标准信号（WCO），壳 stamp 不触发任何修改——**"为某壳做的兼容在另一个壳会再坏"，核心不做壳专属分支**；`web` = 显式「DSH官方Web」，任何情况强制 0；`preset` = 数据驱动的内置壳预设（`src/client/shell-presets.ts`，准入规则：issue/PR 中被提及且 GitHub ⭐>100；v1 仅 anywhere-labs DSH Desktop：darwin advanced 20px、win32 无 WCO 时 32px 兜底；下拉选项命中环境时带「已检测」后缀，仅提示、绝不自动启用）；`custom` = 用户自定义 CSS + 手动 strip px（下拉选中后出现齿轮按钮，弹窗含下移距离与 CSS 输入）。
+  - **旧文档迁移**：schema 中 `titleBarScheme` 无默认值（缺失才可迁移）；旧文档**已有值**（`titleBarCompat === true` 或 `titleBarStripPx` 非默认 40）→ 迁移到 `custom` 方案保留用户数值；干净文档 → `auto`。
+  - **用户空间 CSS**：预设 css（`<style data-dsh-preset-css>`）与自定义 css（`<style data-dsh-custom-css>`）经 `Sidebar.tsx` effect 注入到 `document.head` 末尾（后写胜出；覆盖 JS 内联变量需 `!important`），fiber 卸载/变更即移除。稳定寻址面（皮肤/预设/自定义 CSS 共用）：`[data-dsh-toggle-cluster]`、`[data-dsh-panel]`（右面板）、`[data-dsh-bottom-panel]`（底面板）。
+  - **拖拽区退出**：插件交互 chrome（`.toggleCluster` / `.toggleButton` / `.tabBar`）统一 `-webkit-app-region: no-drag`——无边框壳的顶部拖拽带会吞点击（#103/#111），该属性在普通浏览器与无拖拽区壳中惰性无害。
+  - `compatibility` 模式与无信号环境不避让。
 - **z-index**：面板宿主层 40、折叠按钮簇 45（角手柄在面板内层叠，z-index 2 仅面板内有效）——全部低于 DSH 浮层栈（100/1000+），任何浮层天然盖住侧边栏。
 
 ### 8.2 注意事项
diff --git a/README.md b/README.md
index c74e887..eb0cdab 100644
--- a/README.md
+++ b/README.md
@@ -57,7 +57,8 @@
 
 **✨ 新功能**
 
-- 🖼️ **统一面板宿主注入重构**（[#232](https://github.com/omdsh-dev/DSH-better-sidebar/pull/232)）：面板/开关簇迁入 `[data-dsh-panel-host]` 固定含块层（`fixed inset-0 z-40`），免疫桌面套壳中间层 transform 对 fixed 含块的劫持；挂载自检（页面级 transform → `data-dsh-panel-host-degraded` 降级同步，按未修正几何判定、祖先变换消失才退出）；推挤锚点改 `#root [data-dsh-frame] > [data-pane="conversation"]` + `#root` calc 宽度防桌面壳加性溢出；chunk 激活重验证（HEAD+ETag 保留未变 chunk，5s 超时兜底 fail-open）；桌面信号自动探测（win32 advanced 标题栏兼容 32px 避让，手动 pref 可覆盖）；`visualViewport` 键盘 inset + `env(safe-area-inset-*)` 移动端适配
+- 🧩 **桌面兼容四选项**：位置兼容模式改为**主行下拉**——**自动检测**（默认，保守：仅使用标准的 Window Controls Overlay 几何，32/36px 等各壳差异自动跟随、最大化/还原实时更新，网页环境零修改）/ **DSH官方Web**（显式零适配）/ **壳兼容方案**（内置预设，手动启用；只收录 issue/PR 中出现过且 100+ star 的壳，命中环境带「已检测」提示）/ **自定义方案**（自定义 CSS + 下移距离，保留设置按钮）。旧版本已有兼容配置的用户自动落到自定义方案。核心不再为具体壳写适配分支；交互控件统一退出桌面拖拽区（`no-drag`，吸收 #111/#153）；推挤锚点复合选择器加固（`[data-pane]` 与 `:has(> [data-slot])` 双保险）
+- 🖼️ **统一面板宿主注入重构**（[#232](https://github.com/omdsh-dev/DSH-better-sidebar/pull/232)）：面板/开关簇迁入 `[data-dsh-panel-host]` 固定含块层（`fixed inset-0 z-40`），免疫桌面套壳中间层 transform 对 fixed 含块的劫持；挂载自检（页面级 transform → `data-dsh-panel-host-degraded` 降级同步，按未修正几何判定、祖先变换消失才退出）；推挤锚点改 `#root [data-dsh-frame] > [data-pane="conversation"]` + `#root` calc 宽度防桌面壳加性溢出；chunk 激活重验证（HEAD+ETag 保留未变 chunk，5s 超时兜底 fail-open）；`visualViewport` 键盘 inset + `env(safe-area-inset-*)` 移动端适配
 - 📂 **文件打开方式默认独立**（[#232](https://github.com/omdsh-dev/DSH-better-sidebar/pull/232)）：`editorExplorer` 默认从「合并」改为「独立」——新会话树点击 / 打开文件按路径**新开**文件 tab，无路径窗口即纯资源管理器；合并模式保留为可选手动开启
 - 🖥️ **终端 shell / shellArgs 设置页可配**（[#232](https://github.com/omdsh-dev/DSH-better-sidebar/pull/232)）：终端卡齿轮二级页面新增「Shell 路径」「Shell 参数」两行配置（此前只能通过 `cordis.patch.yml` 配置）——设置页写入后对**之后打开的** UI 终端与模型终端（`terminal_create`）即时生效；留空保持 yaml → `$SHELL` / 登录 shell / `powershell.exe` 的既有解析顺序
 - 🏷️ **设置页版本徽标**（[#232](https://github.com/omdsh-dev/DSH-better-sidebar/pull/232)）：侧边卡片设置页顶部新增 `DSH-better-sidebar v0.14.0` 身份徽标（版本与服务实例同步，由测试守护）
diff --git a/README_EN.md b/README_EN.md
index b39024d..2b2e3ee 100644
--- a/README_EN.md
+++ b/README_EN.md
@@ -56,7 +56,8 @@
 
 **✨ New features**
 
-- 🖼️ **Unified panel-host injection refactor** ([#232](https://github.com/omdsh-dev/DSH-better-sidebar/pull/232)): panels/toggle clusters moved into a `[data-dsh-panel-host]` fixed containing block (`fixed inset-0 z-40`), immune to desktop-shell intermediate transforms hijacking `fixed`; mount self-check (page-level transform → `data-dsh-panel-host-degraded` degraded sync, judged on uncorrected geometry, exits only when the ancestor transform is gone); push anchor switched to `#root [data-dsh-frame] > [data-pane="conversation"]` + `#root` calc width against desktop-shell additive overflow; chunk revalidation on activation (HEAD+ETag keeps unchanged chunks, 5s timeout fails open); desktop signal auto-detection (win32 advanced title-bar compat 32px avoidance, manual pref overrides); `visualViewport` keyboard inset + `env(safe-area-inset-*)` mobile adaptation
+- 🧩 **Desktop compatibility in four options**: "Position compatibility mode" is now a main-row dropdown — **Auto-detect** (default, conservative: only the standard Window Controls Overlay geometry contributes; real 32/36px caption-overlay heights per shell, live on maximize/restore; zero modification on plain web) / **DSH official web** (explicitly no adaptation) / **Shell preset** (built-in, opt-in; only shells that appeared in this repo's issues/PRs with 100+ stars, "detected" badge when the environment matches) / **Custom** (free-form CSS + shift distance, keeps the settings button). Documents that already carried compatibility values migrate to the custom scheme. The core no longer branches per shell; interactive chrome opts out of desktop drag regions (`no-drag`, absorbing #111/#153); the bottom-push anchor is a composite selector (`[data-pane]` and `:has(> [data-slot])` — same element, double protection)
+- 🖼️ **Unified panel-host injection refactor** ([#232](https://github.com/omdsh-dev/DSH-better-sidebar/pull/232)): panels/toggle clusters moved into a `[data-dsh-panel-host]` fixed containing block (`fixed inset-0 z-40`), immune to desktop-shell intermediate transforms hijacking `fixed`; mount self-check (page-level transform → `data-dsh-panel-host-degraded` degraded sync, judged on uncorrected geometry, exits only when the ancestor transform is gone); push anchor switched to `#root [data-dsh-frame] > [data-pane="conversation"]` + `#root` calc width against desktop-shell additive overflow; chunk revalidation on activation (HEAD+ETag keeps unchanged chunks, 5s timeout fails open); `visualViewport` keyboard inset + `env(safe-area-inset-*)` mobile adaptation
 - 📂 **Separate file windows by default** ([#232](https://github.com/omdsh-dev/DSH-better-sidebar/pull/232)): `editorExplorer` now defaults to **separate** — tree clicks / file opens create a new tab per path and the path-less window is a pure file manager; merged mode stays available as an opt-in
 - 🖥️ **Terminal shell / shellArgs configurable from the settings page** ([#232](https://github.com/omdsh-dev/DSH-better-sidebar/pull/232)): the terminal card's gear popup gains "Shell path" and "Shell arguments" rows (previously yaml-only via `cordis.patch.yml`) — saved values take effect immediately for terminals opened afterwards (UI terminals and model `terminal_create` alike); empty keeps the existing yaml → `$SHELL` / login shell / `powershell.exe` resolution order
 - 🏷️ **Version badge on the settings page** ([#232](https://github.com/omdsh-dev/DSH-better-sidebar/pull/232)): the side-card settings section now opens with a `DSH-better-sidebar v0.14.0` identity badge (version synced with the service instance, test-guarded)
diff --git a/docs/plans/2026-08-20-desktop-scheme-settings-design.md b/docs/plans/2026-08-20-desktop-scheme-settings-design.md
new file mode 100644
index 0000000..a8cb28a
--- /dev/null
+++ b/docs/plans/2026-08-20-desktop-scheme-settings-design.md
@@ -0,0 +1,79 @@
+# 桌面端兼容统一方案：四选项下拉（自动检测 / DSH官方Web / 壳预设 / 自定义 CSS）
+
+> 2026-08-20 · 对应分支 `feat/desktop-scheme-settings` · 关联 issue #257、#208、#103/#111；外部 PR #82/#89/#111/#153/#226/#243 处置见文末。
+
+## 背景与问题
+
+better-sidebar 的桌面端适配历史上是"每壳一条补丁"：右上角开关簇与原生标题栏按钮重叠（#87/#101）、点击被拖拽区吞掉（#103/#111）、推挤锚点随 DSH DOM 版本漂移（#208/#226/#262）、WCO 高度硬编码 32px 与实际不符（#257，Electron 版本间 32/36px 不一）。这些补丁全部针对**具体某个壳的 DOM/类名/数值**，换一个壳（Tauri、Pake、新壳）就失效或出错。
+
+**全仓证据盘点**（121 issues + 159 PRs 全量 + 三个候选壳克隆取证）：
+
+| 壳 | ⭐ | issue/PR 提及 | 形态 | 需要什么 |
+|---|---|---|---|---|
+| anywhere-labs/deepseek-harness-desktop | 16.3K | ✅ 大量 | Electron；advanced: win32 WCO 32px / darwin caption 20px；compat 原生框 | win32 已被标准 WCO 覆盖；darwin 20px 让位 |
+| dataelement/dsh-desktop | 1.3K | ❌ 零提及 | Electron；win32 WCO 36px | 已被标准 WCO 覆盖 |
+| Deepseek-Harness-EAC | 1.0K | ❌ 零提及 | Electron Win-only；自绘 36px 玻璃栏（私有标记 `data-dsh-title-bar-height`） | 无 WCO，需 36px 让位（文档示例） |
+| hairyf Tauri 版 | 715 | ✅ pr#229 | Tauri2；44px 导航栏在 iframe **之上** | **无冲突**，无需适配 |
+
+平台分布结论：兼容问题**不是 Windows 独有**（macOS 6 条、Web 3 条），但当前 main 上未闭环的 chrome 兼容基本就是 **Windows 顶栏**（WCO 几何 + 通用 no-drag 兜底）；macOS 的坏 bug（#25/#208）已修复。
+
+## 决策
+
+1. **核心只留 Web 标准机制**：WCO（`navigator.windowControlsOverlay` + `geometrychange`）是唯一"不是适配、是标准"的信号；`-webkit-app-region: no-drag` 是标准属性（普通浏览器/无拖拽区壳惰性无害）。核心代码 grep 不到任何壳类名。
+2. **壳专属适配进用户空间**：「位置兼容模式」升级为**主行下拉**四选项：**自动检测（默认，保守，web 零修改）/ DSH官方Web（显式零适配）/ 壳兼容方案（内置预设，opt-in）/ 自定义方案（自由 CSS + 下移 px，保留齿轮弹窗）**。
+3. **预设准入规则**：issue/PR 中被提及（链接或明确名称）且 GitHub ⭐>100 的壳；v1 仅 anywhere-labs（唯一同时满足者）。预设只做**标题栏 strip 让位**，不做布局推挤/壳类名（尊重"不特意兼容 DSH Desktop 高级模式"）。Tauri 无冲突只写文档；EAC 未提及但提供 custom CSS 示例。
+4. 不向 anywhere-labs 提跨仓库 PR；不修改 DSH 源码。
+
+## 实施
+
+### prefs 模型（`src/prefs-shared.ts` / `src/config.ts` / `src/client/prefs.ts`）
+
+- 新增 `titleBarScheme: 'auto' | 'web' | 'preset' | 'custom'`（默认 `'auto'`）、`titleBarPresetId: string`、`customCss: string`。`web` = 显式「DSH官方Web」，取值链最优先强制 0（连 WCO 也不适用）。
+- schema 中三个新字段**无 default**（schemastery 验证：缺失字段不出现在解析结果里）→ `parsePrefs` 在字段缺失时由旧 `titleBarCompat` 派生：`true` → `custom`（保留 `titleBarStripPx`）；`false`/缺失 → `auto`。写路径镜像写旧字段（`titleBarCompat = scheme !== 'auto'`）供降级。
+
+### 标准件（`src/client/wco.ts` + `src/client/titlebar-strip.ts`）
+
+- `wco.ts`：模块级反应式 store（subscribe/getSnapshot，`useSyncExternalStore` 消费），特性检测 `navigator.windowControlsOverlay`，订阅 `geometrychange` 重读矩形（最大化/还原实时更新）；最后订阅者退订时解绑原生监听；`setWcoSourceForTests` 注入测试源。API 抛错视为 present+0（绝不崩布局）。
+- `titlebar-strip.ts`（唯一决策点，纯函数）：**⓪ `web` 方案强制 0 → ① WCO 真实高度（权威，0 也权威；`visible=false` 幽灵 API 视为缺失）→ ② URL `dsh-desktop-titlebar-inset`（0–120 clamp）→ ③ 预设 `stripFor`（仅 preset 方案）→ ④ 手动 `titleBarStripPx`（仅 custom 方案）→ ⑤ 0**。结果驱动 `body[data-dsh-title-bar-compat]` + `--dsh-title-bar-strip`（CSS 契约不变）。
+- `desktop-env.ts`：只做环境报告（desktop/mode/platform/titlebarInset），SSR 安全；移除旧 `win32OverlayTop` 硬编码。
+
+### 预设与用户 CSS（`src/client/shell-presets.ts` + `Sidebar.tsx` effect）
+
+- `ShellPreset { id; title; desc; stripFor?; css?; detect? }`；v1 一条 `dsh-desktop`：darwin advanced 20px、win32 advanced 32px（无 WCO 兜底）、其余 undefined；`detect` 仅用于设置页「已检测」徽标。
+- 注入：预设 css → `<style data-dsh-preset-css="<id>">`；自定义 css → `<style data-dsh-custom-css="custom">`；追加到 `document.head` 末尾（后写胜出），fiber 卸载/变更即移除。
+- 稳定寻址面：`[data-dsh-toggle-cluster]`、`[data-dsh-panel]`、`[data-dsh-bottom-panel]` data 属性。
+
+### no-drag 兜底（`sidebar.module.css`）
+
+`.toggleCluster` / `.toggleButton` / `.tabBar` 统一 `-webkit-app-region: no-drag`（吸收 #111/#153，补 #103 插件侧缺口）。
+
+### Web 推挤锚点加固（`layout.css`）
+
+复合选择器（同元素双保险）：`#root [data-dsh-frame] > [data-pane="conversation"]` 与 `#root :has(> [data-slot="conversation"])`；拖拽过渡/prefers-reduced-motion 同步；`drag-layout.e2e.ts` 新增两选择器同元素断言。
+
+### 设置 UI（`SideCardSection.tsx` + locales）
+
+「位置兼容模式」行改为**主行下拉**：自动检测（默认）/ DSH官方Web / 各壳预设（命中环境带「已检测」后缀，仅提示）/ 自定义方案（选中后行内出现齿轮，弹窗 = 下移距离 + CSS textarea（Cmd/Ctrl+Enter 提交））。
+
+### 测试
+
+- 单测：`wco.spec.ts`（7 例：检测/读取/取整/geometrychange 通知/抛错降级/换源）、`titlebar-strip.spec.ts`（取值链 5 例）、`shell-presets.spec.ts`（注册表完整性 + dsh-desktop strip 值）、`desktop-env.spec.ts`（重写：inset 参数 clamp + 移除 win32 硬编码）、`prefs.spec.ts`（新字段 + 旧字段迁移）、`plugin-shape.spec.ts`（schema 无默认值语义）、`smoke.spec.ts`（解析结果不含新字段）。
+- e2e（`mount.e2e.ts` 重写桌面场景）：保守 auto（stamp 不触发修改 + data 属性 + no-drag 规则存在）、WCO mock 驱动 strip 且 geometrychange 反应、预设注入（settings.update 写入 scheme=preset → 32px + style 标签）、自定义 CSS 注入（marker 生效）；`drag-layout.e2e.ts` 复合锚点。
+
+## 验证
+
+- `pnpm typecheck` / `pnpm test`（691 passed）/ `pnpm test:mount` 全绿。
+- 普通浏览器零行为变化（auto 无 WCO → 无 strip）。
+- Electron WCO win32（mock 实测）：strip=真实高度（32/36），最大化/还原跟随。
+- anywhere-labs darwin advanced：启用预设后 20px 让位。
+- 核心代码 grep 无壳类名（`.dshDesktopFrame` 等仅存在于预设数据字符串与测试断言之外——v1 预设无 CSS，纯 strip 数据）。
+
+## 实施偏差记录
+
+- 无。计划与实施一致；仅补充：schema 新字段必须无 default 才能让旧文档迁移（否则 settings 服务会把 default 填进解析结果、吞掉迁移），`plugin-shape.spec.ts` 断言了这一点。
+
+## 存量 PR/issue 处置（合并后执行，均含哲学声明）
+
+- 实现后关闭：#257（WCO 标准件）。
+- 关闭：#111/#153（no-drag 吸收）、#226（复合锚点吸收，main 已修）、#243（布局推挤不采纳；标题栏部分进 dsh-desktop 预设）、#108（#232 已吸收 + WCO）、#82/#89/#138（不采纳，指向自定义 CSS/预设路径）。
+- 回复：#208（已修+回归）、#221（自定义 CSS 可微调）、#233（git.ts windowsHide 独立问题）、#167/#240（非 chrome 范畴/文档已有）。
diff --git a/src/client/SideCardSection.module.css b/src/client/SideCardSection.module.css
index 293307c..f55fdef 100644
--- a/src/client/SideCardSection.module.css
+++ b/src/client/SideCardSection.module.css
@@ -462,6 +462,28 @@
   color: var(--dsw-alias-label-secondary);
 }
 
+/* The multi-line custom-CSS input (scheme `custom`): monospace, generous
+   height, resizable — same surface tokens as the typed inputs. */
+.cssTextArea {
+  width: 100%;
+  box-sizing: border-box;
+  min-height: 120px;
+  padding: 8px 10px;
+  border: 1px solid var(--dsw-alias-border-l2);
+  border-radius: 8px;
+  background: var(--dsw-alias-bg-layer-3);
+  color: var(--dsw-alias-label-primary);
+  font-family: var(--ds-font-family-code, monospace);
+  font-size: 12px;
+  line-height: 1.6;
+  resize: vertical;
+}
+
+.cssTextArea:focus-visible {
+  outline: 2px solid var(--dsw-alias-state-business-primary);
+  outline-offset: 2px;
+}
+
 /* Secondary settings popup: a wider dialog than the primitive default (the
    dialog portals to document.body; the doubled class keeps the width rule
    above the primitive's .dialog regardless of stylesheet order). */
diff --git a/src/client/SideCardSection.tsx b/src/client/SideCardSection.tsx
index 4da11c7..efbc0df 100644
--- a/src/client/SideCardSection.tsx
+++ b/src/client/SideCardSection.tsx
@@ -38,7 +38,7 @@
  * shows the wire error inline — a broken settings surface never crashes the
  * shell.
  */
-import { Fragment, useEffect, useRef, useState, type ReactNode } from 'react'
+import { Fragment, useEffect, useMemo, useRef, useState, type ReactNode } from 'react'
 import {
   IconCheckOutline16,
   IconChevronDownOutline14,
@@ -59,11 +59,14 @@ import {
   WIDTH_PERCENT_MAX,
   WIDTH_PERCENT_MIN,
   type SidebarPrefs,
+  type TitleBarScheme,
 } from '../prefs-shared.ts'
 import { api } from './api.ts'
 import { parsePrefs } from './prefs.ts'
 import { AddPluginModal, type PluginKind } from './add-plugin-modal.tsx'
 import { t } from './locales.ts'
+import { parseDesktopEnv } from './desktop-env.ts'
+import { getShellPreset, getShellPresets } from './shell-presets.ts'
 import type { SidebarStore } from './state.ts'
 import type {
   BetterSidebarService,
@@ -109,6 +112,17 @@ function tabOrder(a: TabDescriptor, b: TabDescriptor): number {
   return (a.order ?? 100) - (b.order ?? 100)
 }
 
+/**
+ * The scheme dropdown's current value: the plain scheme, or `preset:<id>`
+ * while a preset is active. Falls back to `auto` when the stored preset id
+ * is no longer registered (the strip resolves to 0 then anyway).
+ */
+function titleBarSchemeValue(prefs: SidebarPrefs): string {
+  if (prefs.titleBarScheme !== 'preset') return prefs.titleBarScheme
+  const preset = getShellPreset(prefs.titleBarPresetId)
+  return preset !== undefined ? `preset:${preset.id}` : 'auto'
+}
+
 /** Viewer inventory order: priority desc (the catch-all `code` comes last). */
 function viewerOrder(a: FileViewerDescriptor, b: FileViewerDescriptor): number {
   return (b.priority ?? 0) - (a.priority ?? 0)
@@ -318,24 +332,60 @@ function TypedRow(props: {
     </div>
   )
 }
+/**
+ * The multi-line custom-CSS input (scheme `custom`): a monospace textarea
+ * whose draft is local state, committed on blur or Cmd/Ctrl+Enter through
+ * the parent's handler. Keyed by the stored value so an external commit
+ * remounts it with the canonical text (same pattern as TypedRow).
+ */
+function CssDraft(props: {
+  value: string
+  onCommit: (raw: string) => void
+  label: string
+  placeholder?: string
+}) {
+  const { value, onCommit, label, placeholder } = props
+  const [draft, setDraft] = useState(value)
+  return (
+    <textarea
+      className={css.cssTextArea}
+      rows={6}
+      value={draft}
+      placeholder={placeholder}
+      aria-label={label}
+      spellCheck={false}
+      onChange={event => { setDraft(event.currentTarget.value) }}
+      onBlur={() => { onCommit(draft) }}
+      onKeyDown={event => {
+        if (event.key === 'Enter' && (event.metaKey || event.ctrlKey)) event.currentTarget.blur()
+      }}
+    />
+  )
+}
 
 /**
- * One select row: a dropdown over the toggle's declared `options`. When any
- * option carries an icon, the dropdown renders big-icon option cards (icon +
- * title + desc) and the closed anchor shows the selected option's icon as
- * well; without icons both are a single line of text. Single-pick commits the
- * option's value and closes; `multi` toggles membership, commits the picked
- * values as an array (in options order), and stays open.
+ * The reusable dropdown — the primitives Menu, NOT a native <select>: a
+ * closed anchor button (picked option text + chevron) opening one Menu item
+ * per option (big-icon cards when any option carries an icon). Single-pick
+ * commits the option's value and closes; `multi` toggles membership and
+ * commits the picked values as an array (in options order), staying open.
+ * Shared by the declarative select rows (SelectRow) and the title-bar
+ * scheme dropdown on the General row.
  */
-function SelectRow(props: {
-  toggle: SidebarSettingToggle
-  title: string
+function SelectMenu(props: {
+  label: string
   value: unknown
-  onSelectValue?: (toggle: SidebarSettingToggle, next: unknown) => void
+  options: readonly {
+    value: string | number | boolean
+    title: string | (() => string)
+    desc?: string | (() => string)
+    icon?: ReactNode | ((size: number) => ReactNode)
+  }[]
+  multi?: boolean
+  onSelect: (next: unknown) => void
+  placeholder?: string
 }) {
-  const { toggle, title, value, onSelectValue } = props
-  const options = toggle.options ?? []
-  const multi = toggle.multi === true
+  const { label, value, options, multi, onSelect, placeholder } = props
   const [open, setOpen] = useState(false)
   const hasIcons = options.some(option => option.icon !== undefined)
   const picked: readonly unknown[] = multi ? (Array.isArray(value) ? value : []) : [value]
@@ -346,7 +396,7 @@ function SelectRow(props: {
     const option = options[index]
     if (option === undefined) return
     if (!multi) {
-      onSelectValue?.(toggle, option.value)
+      onSelect(option.value)
       setOpen(false)
       return
     }
@@ -355,14 +405,14 @@ function SelectRow(props: {
     if (at >= 0) current.splice(at, 1)
     else current.push(option.value)
     // Stable wire order: follow the declared options order, not pick order.
-    onSelectValue?.(toggle, options.filter(o => current.includes(o.value)).map(o => o.value))
+    onSelect(options.filter(o => current.includes(o.value)).map(o => o.value))
   }
 
   const anchor = (
     <button
       type="button"
       className={css.selectAnchor}
-      aria-label={title}
+      aria-label={label}
       aria-haspopup="listbox"
       aria-expanded={open}
       onClick={() => { setOpen(now => !now) }}
@@ -371,12 +421,55 @@ function SelectRow(props: {
         <span className={css.selectAnchorIcon}>{iconOf(selected[0].icon, 16)}</span>
       )}
       <span className={css.selectAnchorText}>
-        {selected.length === 0 ? '—' : selected.map(option => textOf(option.title)).join(', ')}
+        {selected.length === 0 ? (placeholder ?? '—') : selected.map(option => textOf(option.title)).join(', ')}
       </span>
       <IconChevronDownOutline14 size={12} />
     </button>
   )
 
+  return (
+    <Menu
+      open={open}
+      anchor={anchor}
+      items={options.map((option, index) => ({
+        id: String(index),
+        label: hasIcons
+          ? (
+            <span className={css.selectOption}>
+              <span className={css.selectOptionIcon}>{iconOf(option.icon, 24)}</span>
+              <span className={css.selectOptionText}>
+                <span className={css.title}>{textOf(option.title)}</span>
+                {textOf(option.desc) !== '' && <span className={css.desc}>{textOf(option.desc)}</span>}
+              </span>
+            </span>
+          )
+          : textOf(option.title),
+      }))}
+      selectedId={!multi && selected[0] !== undefined ? String(options.indexOf(selected[0])) : undefined}
+      selectedIds={multi ? selected.map(option => String(options.indexOf(option))) : undefined}
+      onSelect={(id) => { pick(Number(id)) }}
+      onClose={() => { setOpen(false) }}
+      portal
+    />
+  )
+}
+
+/**
+ * One select row: a dropdown over the toggle's declared `options` (the
+ * shared SelectMenu). When any option carries an icon, the dropdown renders
+ * big-icon option cards (icon + title + desc) and the closed anchor shows
+ * the selected option's icon as well; without icons both are a single line
+ * of text. Single-pick commits the option's value and closes; `multi`
+ * toggles membership, commits the picked values as an array (in options
+ * order), and stays open.
+ */
+function SelectRow(props: {
+  toggle: SidebarSettingToggle
+  title: string
+  value: unknown
+  onSelectValue?: (toggle: SidebarSettingToggle, next: unknown) => void
+}) {
+  const { toggle, title, value, onSelectValue } = props
   return (
     <div className={css.popupRow}>
       <span className={css.rowText}>
@@ -384,28 +477,12 @@ function SelectRow(props: {
         {textOf(toggle.desc) !== '' && <span className={css.desc}>{textOf(toggle.desc)}</span>}
       </span>
       <span className={css.control}>
-        <Menu
-          open={open}
-          anchor={anchor}
-          items={options.map((option, index) => ({
-            id: String(index),
-            label: hasIcons
-              ? (
-                <span className={css.selectOption}>
-                  <span className={css.selectOptionIcon}>{iconOf(option.icon, 24)}</span>
-                  <span className={css.selectOptionText}>
-                    <span className={css.title}>{textOf(option.title)}</span>
-                    {textOf(option.desc) !== '' && <span className={css.desc}>{textOf(option.desc)}</span>}
-                  </span>
-                </span>
-              )
-              : textOf(option.title),
-          }))}
-          selectedId={!multi && selected[0] !== undefined ? String(options.indexOf(selected[0])) : undefined}
-          selectedIds={multi ? selected.map(option => String(options.indexOf(option))) : undefined}
-          onSelect={(id) => { pick(Number(id)) }}
-          onClose={() => { setOpen(false) }}
-          portal
+        <SelectMenu
+          label={title}
+          value={value}
+          options={toggle.options ?? []}
+          multi={toggle.multi === true}
+          onSelect={(next) => { onSelectValue?.(toggle, next) }}
         />
       </span>
     </div>
@@ -498,6 +575,10 @@ export function SideCardSection({ store, service }: SideCardSectionProps) {
   const [settingsFor, setSettingsFor] = useState<TabDescriptor | FileViewerDescriptor | null>(null)
   // Whether the position-compat strip popup (the gear on the 常规 row) is open.
   const [stripSettingsOpen, setStripSettingsOpen] = useState(false)
+  // The parsed desktop environment (URL stamps — see desktop-env.ts). Used
+  // ONLY to badge matching presets in the scheme dropdown ("已检测");
+  // nothing is auto-applied.
+  const detectedEnv = useMemo(() => parseDesktopEnv(), [])
   // Whether the "add plugin" modal (a dashed card at the end of the
   // 侧边栏内容 / 文件预览 grids) is open, and for which extension point
   // (null = closed).
@@ -635,6 +716,38 @@ export function SideCardSection({ store, service }: SideCardSectionProps) {
     return raw
   }
 
+  /**
+   * Pick the title-bar / shell compatibility scheme. Mirrors the legacy
+   * `titleBarCompat` flag (true = anything but the conservative auto) so
+   * documents stay readable by older plugin versions.
+   */
+  /**
+   * Pick the title-bar / shell compatibility scheme from the dropdown. The
+   * option values are `auto` | `web` | `custom` | `preset:<id>`; selecting
+   * a preset stores both the scheme and its id. Mirrors the legacy
+   * `titleBarCompat` flag (true for preset/custom) so documents stay
+   * readable by older plugin versions.
+   */
+  const onSchemeSelect = (value: unknown): void => {
+    if (typeof value !== 'string') return
+    if (value === 'auto' || value === 'web' || value === 'custom') {
+      applyPref({ titleBarScheme: value, titleBarCompat: value === 'custom' })
+      return
+    }
+    if (value.startsWith('preset:') && getShellPreset(value.slice('preset:'.length)) !== undefined) {
+      applyPref({
+        titleBarScheme: 'preset',
+        titleBarPresetId: value.slice('preset:'.length),
+        titleBarCompat: true,
+      })
+    }
+  }
+
+  /** Commit the free-form custom CSS (scheme `custom`). */
+  const commitCustomCss = (raw: string): void => {
+    applyPref({ customCss: raw })
+  }
+
   /** Persist one plugin-owned setting of one descriptor (merged into the pluginSettings blob). */
   const applyPluginSetting = (descriptorId: string, key: string, value: unknown): void => {
     applyPref({ pluginSettings: mergePluginSetting(optimisticRef.current.pluginSettings, descriptorId, key, value) })
@@ -800,12 +913,31 @@ export function SideCardSection({ store, service }: SideCardSectionProps) {
           </span>
           <span className={css.control}>
             {/*
-              The position-compat row's gear (same popup pattern as the
-              feature cards): opens a Modal with the strip-height number row.
-              Hidden while the mode is off — its related setting is dormant
-              then (the feature-card convention).
+              The scheme dropdown (the shared SelectMenu — NOT a native
+              select): 自动检测 (default) / DSH官方Web / 各壳兼容方案 /
+              自定义方案. Matching presets carry a 「已检测」 desc badge
+              (suggestion only). The 自定义方案 row keeps its gear (the
+              popup with the shift distance + custom CSS) — the other
+              schemes need no further settings.
             */}
-            {prefs.titleBarCompat && (
+            <SelectMenu
+              label={t('settingsTitleBarTitle')}
+              value={titleBarSchemeValue(prefs)}
+              options={[
+                { value: 'auto', title: t('settingsSchemeAutoTitle'), desc: t('settingsSchemeAutoDesc') },
+                { value: 'web', title: t('settingsSchemeWebTitle'), desc: t('settingsSchemeWebDesc') },
+                ...getShellPresets().map(preset => ({
+                  value: `preset:${preset.id}`,
+                  title: preset.title,
+                  desc: preset.detect?.(detectedEnv) === true
+                    ? `${preset.desc}（${t('settingsSchemeDetectedSuffix')}）`
+                    : preset.desc,
+                })),
+                { value: 'custom', title: t('settingsSchemeCustomTitle'), desc: t('settingsSchemeCustomDesc') },
+              ]}
+              onSelect={onSchemeSelect}
+            />
+            {prefs.titleBarScheme === 'custom' && (
               <button
                 type="button"
                 className={css.rowGear}
@@ -816,11 +948,6 @@ export function SideCardSection({ store, service }: SideCardSectionProps) {
                 <IconSettingsOutline16 size={14} />
               </button>
             )}
-            <Switch
-              label={t('settingsTitleBarTitle')}
-              checked={prefs.titleBarCompat}
-              onChange={(next) => { applyPref({ titleBarCompat: next }) }}
-            />
           </span>
         </div>
       </div>
@@ -948,10 +1075,11 @@ export function SideCardSection({ store, service }: SideCardSectionProps) {
         </Modal>
       )}
 
-      {/* The position-compat strip popup (opened by the gear on the 常规
-          row): one number row for the reserved strip height in px. Same
-          Modal chrome and row machinery as the feature popups — mounted
-          only while open (the Modal SSR rule above). */}
+      {/* The custom-scheme popup (opened by the gear next to the scheme
+          dropdown when 自定义方案 is active): the shift distance in px and
+          the free-form custom CSS. The OTHER schemes (自动检测 / DSH官方Web /
+          壳预设) need no further settings — the scheme itself is chosen on
+          the 常规 row. Mounted only while open (the Modal SSR rule above). */}
       {stripSettingsOpen && (
         <Modal
           open
@@ -966,20 +1094,29 @@ export function SideCardSection({ store, service }: SideCardSectionProps) {
             </button>
           )}
         >
-          <FeatureSettingsRows
-            toggles={[{
-              key: 'titleBarStripPx',
-              type: 'number',
-              title: () => t('settingsTitleBarStripTitle'),
-              desc: () => t('settingsTitleBarStripDesc'),
-              min: TITLE_BAR_STRIP_MIN,
-              max: TITLE_BAR_STRIP_MAX,
-              unit: 'px',
-            }]}
-            prefs={prefs}
-            onToggle={onToggleSetting}
-            onCommit={onCommitSetting}
-          />
+          <div className={css.popupRows}>
+            <FeatureSettingsRows
+              toggles={[{
+                key: 'titleBarStripPx',
+                type: 'number',
+                title: () => t('settingsTitleBarStripTitle'),
+                desc: () => t('settingsTitleBarStripDesc'),
+                min: TITLE_BAR_STRIP_MIN,
+                max: TITLE_BAR_STRIP_MAX,
+                unit: 'px',
+              }]}
+              prefs={prefs}
+              onToggle={onToggleSetting}
+              onCommit={onCommitSetting}
+            />
+            <CssDraft
+              key={prefs.customCss}
+              value={prefs.customCss}
+              label={t('settingsCustomCssTitle')}
+              placeholder={t('settingsCustomCssPlaceholder')}
+              onCommit={commitCustomCss}
+            />
+          </div>
         </Modal>
       )}
 
diff --git a/src/client/Sidebar.tsx b/src/client/Sidebar.tsx
index 6a09d2a..5684db7 100644
--- a/src/client/Sidebar.tsx
+++ b/src/client/Sidebar.tsx
@@ -44,6 +44,9 @@ import { IconPanelBottomOutline16, IconPanelRightOutline16 } from './icons.tsx'
 import { Workbench, type WorkbenchActions } from './split-pane.tsx'
 import { useNarrowViewport } from './breakpoints.ts'
 import { parseDesktopEnv } from './desktop-env.ts'
+import { getWcoSnapshot, subscribeWco } from './wco.ts'
+import { getShellPreset } from './shell-presets.ts'
+import { computeTitleBarStrip } from './titlebar-strip.ts'
 import type { NewTabOption } from './TabBar.tsx'
 import type { TabDragPayload } from './TabBar.tsx'
 import { relativeTo } from './paths.ts'
@@ -86,6 +89,20 @@ const osFileDragShield = {
   onDrop: swallowOsFileDrag,
 }
 
+/**
+ * Append one user-space stylesheet (preset or custom CSS) as a tagged
+ * `<style>` element. The tag attribute carries the source identity so the
+ * running configuration is inspectable in DevTools; the returned tag is
+ * removed by the caller's effect cleanup.
+ */
+function injectUserCss(attr: string, id: string, cssText: string): HTMLStyleElement {
+  const tag = document.createElement('style')
+  tag.setAttribute(attr, id)
+  tag.textContent = cssText
+  document.head.appendChild(tag)
+  return tag
+}
+
 /** Render the content of one tab (dispatched by type). */
 function TabContent(props: {
   tab: SidebarTab
@@ -229,25 +246,31 @@ export function Sidebar(props: { ctx: Context; store: SidebarStore }) {
     return () => { document.body.removeAttribute('data-dsh-sidebar-collapsed') }
   }, [collapsed])
 
-  // Position compatibility mode (titleBarCompat pref): Windows frameless
-  // windows draw the native title bar (minimize/maximize/close) at the
-  // window's top-right corner, OVER the web content. When enabled, the body
-  // attribute lets sidebar.module.css drop the toggle cluster below the
-  // strip and push the right panel's content below it. Auto-enabled in the
-  // win32 advanced desktop shell (the shell stamps the URL — see
-  // desktop-env.ts — and reserves a 32px overlay for the window controls);
-  // the manual pref and its strip height still win when the user sets them,
-  // and the manual switch only ever ADDS compat. The strip height rides a
-  // CSS variable so the rules stay declarative; the attribute rides the
-  // snapshot's prefs, so flipping the setting re-renders and re-applies
-  // immediately; the cleanup removes both on unmount/boundary swap so a
-  // crashed sidebar never leaves them behind.
+  // Title-bar / shell compatibility (the "位置兼容模式" scheme):
+  //   auto    — CONSERVATIVE: only the standard Window Controls Overlay
+  //             geometry contributes (the real caption-overlay height,
+  //             reactive to maximize/restore). No URL stamp, no preset, no
+  //             guess — plain browsers see zero modification.
+  //   preset  — an opt-in built-in shell preset (shell-presets.ts) adds its
+  //             per-shell strip as the no-WCO fallback.
+  //   custom  — the user's own CSS (injected below) + the legacy manual
+  //             strip px.
+  // The resolved strip drives the SAME body attribute + CSS variable as the
+  // legacy boolean did, so the CSS contract is unchanged (layout.css /
+  // sidebar.module.css); only the value source changed. The cleanup removes
+  // both on unmount/boundary swap so a crashed sidebar never leaves them
+  // behind.
   const desktopEnv = parseDesktopEnv()
-  const autoTitleBarCompat = desktopEnv.win32OverlayTop > 0
-  const titleBarCompat = snapshot.prefs.titleBarCompat || autoTitleBarCompat
-  const titleBarStrip = snapshot.prefs.titleBarCompat
-    ? snapshot.prefs.titleBarStripPx
-    : desktopEnv.win32OverlayTop
+  const wco = useSyncExternalStore(
+    useMemo(() => subscribeWco, []),
+    getWcoSnapshot,
+  )
+  const scheme = snapshot.prefs.titleBarScheme
+  const preset = scheme === 'preset' ? getShellPreset(snapshot.prefs.titleBarPresetId) : undefined
+  const titleBarStrip = computeTitleBarStrip(
+    desktopEnv, wco, scheme, preset, snapshot.prefs.titleBarStripPx,
+  )
+  const titleBarCompat = titleBarStrip > 0
   useEffect(() => {
     const root = document.documentElement
     if (titleBarCompat) {
@@ -263,6 +286,22 @@ export function Sidebar(props: { ctx: Context; store: SidebarStore }) {
     }
   }, [titleBarCompat, titleBarStrip])
 
+  // User-space CSS injection (the escape hatch): preset CSS (scheme
+  // `preset`) and free-form custom CSS (scheme `custom`) are appended AFTER
+  // the plugin's own styles — later in the cascade wins ties, and
+  // `!important` can override the JS-written inline strip variable. Each
+  // source gets its own tagged <style> so the running configuration stays
+  // inspectable; tags are removed on change/unmount so a stale stylesheet
+  // never outlives its fiber (HMR-safe).
+  const presetCss = scheme === 'preset' ? preset?.css ?? '' : ''
+  const customCss = scheme === 'custom' ? snapshot.prefs.customCss : ''
+  useEffect(() => {
+    const tags: HTMLStyleElement[] = []
+    if (presetCss !== '') tags.push(injectUserCss('data-dsh-preset-css', preset?.id ?? '', presetCss))
+    if (customCss !== '') tags.push(injectUserCss('data-dsh-custom-css', 'custom', customCss))
+    return () => { for (const tag of tags) tag.remove() }
+  }, [presetCss, customCss, preset?.id])
+
   /**
    * Bottom-panel merge on narrow viewports: whenever a session is current
    * while narrow (mount, session switch, or a desktop→narrow transition),
@@ -891,7 +930,7 @@ export function Sidebar(props: { ctx: Context; store: SidebarStore }) {
   if (state === undefined || sessionId === undefined) {
     return (
       <div data-dsh-panel-host {...osFileDragShield}>
-        <div className={css.toggleCluster}>
+        <div className={css.toggleCluster} data-dsh-toggle-cluster>
           {!narrow && (
             <Tooltip label={t('noSession')} side="bottom" delayMs={500}>
               <button type="button" className={css.toggleButton} disabled aria-label={t('noSession')}>
@@ -985,7 +1024,7 @@ export function Sidebar(props: { ctx: Context; store: SidebarStore }) {
         right end it really squeezes (the strip reserves its width via CSS),
         so the tabs genuinely yield space to it.
       */}
-      <div className={css.toggleCluster}>
+      <div className={css.toggleCluster} data-dsh-toggle-cluster>
         {/*
           Narrow viewports merge the two workbenches into the one drawer —
           there is no bottom panel, so its toggle button is not offered.
@@ -1025,6 +1064,7 @@ export function Sidebar(props: { ctx: Context; store: SidebarStore }) {
       <div
         ref={panelRef}
         className={clsx(css.panel, !state.panelOpen && css.panelHidden)}
+        data-dsh-panel
         style={{
           width: narrow ? '100vw' : Math.min(state.width, window.innerWidth),
           // Narrow drawer: keep the bottom-anchored sheet above the on-screen
@@ -1155,7 +1195,8 @@ export function Sidebar(props: { ctx: Context; store: SidebarStore }) {
       <div
         ref={bottomRef}
         className={clsx(css.bottomPanel, !state.bottomOpen && css.bottomPanelHidden)}
-        data-dsh-bottom-panel=""
+        data-dsh-panel
+        data-dsh-bottom-panel
         style={{
           height: Math.min(state.bottomHeight, window.innerHeight),
           left: centerRect.left,
diff --git a/src/client/desktop-env.ts b/src/client/desktop-env.ts
index 751f67f..49ffdcb 100644
--- a/src/client/desktop-env.ts
+++ b/src/client/desktop-env.ts
@@ -1,21 +1,18 @@
 /**
- * Desktop-shell detection for the sidebar. The official DSH Desktop shell
- * (Electron) stamps every render URL with `dsh-desktop-mode` and
- * `dsh-desktop-platform` and exposes `window.__DSH_DESKTOP_FILE_PATH__`
- * through its preload; community Tauri shells keep the native system frame
- * (no stamps — plain-browser semantics). Parsed once per page and memoized
- * (the URL never changes mid-session); `resetDesktopEnvForTests` clears the
- * memo for unit tests.
+ * Desktop-shell detection for the sidebar. Shells may stamp the render URL
+ * with `dsh-desktop-mode` / `dsh-desktop-platform` (the official Electron
+ * shell does) and expose `window.__DSH_DESKTOP_FILE_PATH__` through a
+ * preload. Parsed once per page and memoized (the URL never changes
+ * mid-session); `resetDesktopEnvForTests` clears the memo for unit tests.
  *
- * Geometry facts the sidebar adapts to (from the Electron runtime):
- * - win32 `advanced` mode draws the window controls in a 32px overlay strip
- *   at the top-right of the web content (`titleBarOverlay: { height: 32 }`)
- *   — exactly where the toggle cluster sits, so it must drop below the
- *   strip and the right panel's content must clear it.
- * - darwin `advanced` mode keeps the traffic lights at (16,16) in the
- *   top-left; nothing on the plugin's side touches that corner today, but
- *   the platform is still reported so left-edge controls can avoid it.
- * - `compatibility` mode keeps the native frame — no adaptation needed.
+ * GEOMETRY POLICY: this module only REPORTS shell facts — it never decides
+ * how to adapt. The strip height comes from standard signals first (the
+ * Window Controls Overlay API, see wco.ts), then the documented contract
+ * parameter `dsh-desktop-titlebar-inset` (a shell may stamp the real pixels
+ * it reserves at the top), then the user's chosen scheme (preset / custom).
+ * The legacy win32-advanced 32px constant is gone from the core: it lives
+ * in the opt-in shell preset (shell-presets.ts) as a fallback for shells
+ * without the WCO API.
  */
 export interface DesktopEnv {
   /** Running inside a desktop shell (any URL stamp or preload marker). */
@@ -24,34 +21,51 @@ export interface DesktopEnv {
   readonly mode: 'compatibility' | 'advanced' | null
   /** Shell platform stamp ('darwin' | 'win32' | …), lowercased, or null. */
   readonly platform: string | null
-  /** Pixels the win32 advanced shell reserves at the top-right for window
-   *  controls (0 elsewhere). */
-  readonly win32OverlayTop: number
+  /**
+   * Contract parameter `dsh-desktop-titlebar-inset`: pixels the shell
+   * reserves at the top of the web content for its own chrome (0–120,
+   * clamped; 0 when absent). Standard WCO geometry takes precedence over
+   * this whenever the API is available.
+   */
+  readonly titlebarInset: number
 }
 
 let cached: DesktopEnv | undefined
 
-/** Read the shell's desktop stamps (memoized per page). */
+/** Read the shell's desktop stamps (memoized per page; SSR-safe). */
 export function parseDesktopEnv(): DesktopEnv {
   if (cached !== undefined) return cached
+  const hasWindow = typeof window !== 'undefined'
+  const hasPreloadMarker = hasWindow
+    && typeof (window as { __DSH_DESKTOP_FILE_PATH__?: unknown }).__DSH_DESKTOP_FILE_PATH__ !== 'undefined'
   // location.search includes the leading '?', which URLSearchParams does NOT
   // strip (it would become part of the first key) — drop it explicitly.
-  const params = new URLSearchParams(window.location.search.replace(/^\?/, ''))
+  // SSR (no window) resolves the empty environment: nothing desktop.
+  const params = hasWindow
+    ? new URLSearchParams(window.location.search.replace(/^\?/, ''))
+    : new URLSearchParams()
   const modeParam = params.get('dsh-desktop-mode')
   const mode = modeParam === 'compatibility' || modeParam === 'advanced' ? modeParam : null
   const platformParam = params.get('dsh-desktop-platform')
   const platform = platformParam !== null && platformParam !== '' ? platformParam.toLowerCase() : null
-  const desktop = mode !== null
-    || typeof (window as { __DSH_DESKTOP_FILE_PATH__?: unknown }).__DSH_DESKTOP_FILE_PATH__ !== 'undefined'
+  const desktop = mode !== null || hasPreloadMarker
   cached = {
     desktop,
     mode,
     platform,
-    win32OverlayTop: desktop && mode === 'advanced' && platform === 'win32' ? 32 : 0,
+    titlebarInset: parseTitlebarInset(params.get('dsh-desktop-titlebar-inset')),
   }
   return cached
 }
 
+/** Clamp the contract inset parameter into 0–120 (invalid/absent → 0). */
+function parseTitlebarInset(raw: string | null): number {
+  if (raw === null) return 0
+  const parsed = Number(raw)
+  if (!Number.isFinite(parsed)) return 0
+  return Math.min(120, Math.max(0, Math.round(parsed)))
+}
+
 /** Test hook: drop the memo so the next parse re-reads the URL/globals. */
 export function resetDesktopEnvForTests(): void {
   cached = undefined
diff --git a/src/client/layout.css b/src/client/layout.css
index 20b4f1f..333f9b0 100644
--- a/src/client/layout.css
+++ b/src/client/layout.css
@@ -35,8 +35,14 @@
     width var(--ds-transition-duration-slow) var(--ds-ease-in-out);
 }
 
-/* The AppFrame's center column, anchored by data attributes (see above). */
-#root [data-dsh-frame] > [data-pane="conversation"] {
+/* The AppFrame's center column, anchored by data attributes (see above).
+   Composite selector: DSH 0.1.x versions name the center grid item
+   `[data-pane="conversation"]`, while rc.8-era shells put a
+   `[data-slot="conversation"]` child inside it — both selectors resolve to
+   the SAME element on live pages (verified), and keeping both future-proofs
+   the rule against a host rename without touching shell-specific markup. */
+#root [data-dsh-frame] > [data-pane="conversation"],
+#root :has(> [data-slot="conversation"]) {
   margin-bottom: var(--dsh-sidebar-height, 0px);
   transition: margin-bottom var(--ds-transition-duration-slow) var(--ds-ease-in-out);
 }
@@ -55,7 +61,8 @@ body[data-dsh-sidebar-collapsed] [data-slot="conversation.session.header"] > hea
 }
 
 body[data-dsh-sidebar-dragging] #root,
-body[data-dsh-sidebar-dragging] #root [data-dsh-frame] > [data-pane="conversation"] {
+body[data-dsh-sidebar-dragging] #root [data-dsh-frame] > [data-pane="conversation"],
+body[data-dsh-sidebar-dragging] #root :has(> [data-slot="conversation"]) {
   transition: none;
 }
 
@@ -80,7 +87,8 @@ body[data-dsh-sidebar-dragging] #root [data-dsh-frame] > [data-pane="conversatio
 
 @media (prefers-reduced-motion: reduce) {
   #root,
-  #root [data-dsh-frame] > [data-pane="conversation"] {
+  #root [data-dsh-frame] > [data-pane="conversation"],
+  #root :has(> [data-slot="conversation"]) {
     transition: none;
   }
 }
diff --git a/src/client/locales.ts b/src/client/locales.ts
index 490ce15..1c06b4b 100644
--- a/src/client/locales.ts
+++ b/src/client/locales.ts
@@ -154,9 +154,19 @@ export const zh = {
   settingsOpenPathTitle: '聊天区文件在侧边栏打开',
   settingsOpenPathDesc: '在聊天里点击文件链接（工具行、产物列表、文件提及）时，在侧边栏编辑器中打开，不再调用系统默认应用',
   settingsTitleBarTitle: '位置兼容模式',
-  settingsTitleBarDesc: '为 Windows 右上角的原生标题栏预留空间：侧边栏按钮与侧边栏内容整体下移，避免被标题栏遮挡',
+  settingsTitleBarDesc: '选择顶栏兼容方案：自动检测（默认，保守）/ DSH官方Web / 已知桌面壳 / 自定义方案（下移距离 + 自定义 CSS）',
   settingsTitleBarStripTitle: '下移距离',
-  settingsTitleBarStripDesc: '标题栏条带高度：侧边栏按钮与内容下移的像素数（0–120，默认 40）',
+  settingsTitleBarStripDesc: '标题栏条带高度：侧边栏按钮与内容下移的像素数（0–120，默认 40；自定义方案下生效）',
+  settingsSchemeAutoTitle: '自动检测',
+  settingsSchemeAutoDesc: '保守方案：仅在 Window Controls Overlay 标准 API 可用时按真实标题栏高度让位；网页环境下不做任何修改',
+  settingsSchemeWebTitle: 'DSH官方Web',
+  settingsSchemeWebDesc: '显式声明运行在官方网页版：不做任何适配（连标准 WCO 几何也不适用）',
+  settingsSchemeCustomTitle: '自定义方案',
+  settingsSchemeCustomDesc: '完全由你控制：注入自定义 CSS（可覆盖内置样式），并指定标题栏下移距离',
+  settingsSchemeDetectedSuffix: '已检测',
+  settingsCustomCssTitle: '自定义 CSS',
+  settingsCustomCssDesc: '追加到页面末尾的样式（同优先级下后写胜出；覆盖 JS 内联变量需用 !important）',
+  settingsCustomCssPlaceholder: '/* 例：为自绘标题栏的壳预留 36px */\nhtml[data-dsh-title-bar-height="36"] {\n  --dsh-title-bar-strip: 36px !important;\n}',
   settingsSaveFailed: '保存失败',
   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',
@@ -422,9 +432,19 @@ export const en: Record<keyof typeof zh, string> = {
   settingsOpenPathTitle: 'Open chat files in the sidebar',
   settingsOpenPathDesc: 'Open file links in the chat (tool rows, produced files, mentions) in the sidebar editor instead of the system default app',
   settingsTitleBarTitle: 'Position compatibility mode',
-  settingsTitleBarDesc: 'Reserve space for the native Windows title bar at the top-right so the sidebar buttons and content sit below it instead of underneath',
+  settingsTitleBarDesc: 'Pick the title-bar compatibility scheme: auto-detect (default, conservative) / DSH official web / known desktop shells / custom (shift distance + custom CSS)',
   settingsTitleBarStripTitle: 'Shift distance',
-  settingsTitleBarStripDesc: 'Title-bar strip height: how far the sidebar buttons and content move down in px (0–120, default 40)',
+  settingsTitleBarStripDesc: 'Title-bar strip height: how far the sidebar buttons and content move down in px (0–120, default 40; applies under the custom scheme)',
+  settingsSchemeAutoTitle: 'Auto-detect',
+  settingsSchemeAutoDesc: 'Conservative: only the standard Window Controls Overlay API contributes (real caption-overlay height); plain web environments get no modification',
+  settingsSchemeWebTitle: 'DSH official web',
+  settingsSchemeWebDesc: 'Explicitly declare the official web UI: no adaptation at all (not even standard WCO geometry)',
+  settingsSchemeCustomTitle: 'Custom',
+  settingsSchemeCustomDesc: 'Full control: inject custom CSS (can override built-in styles) and set the title-bar shift distance',
+  settingsSchemeDetectedSuffix: 'detected',
+  settingsCustomCssTitle: 'Custom CSS',
+  settingsCustomCssDesc: 'Styles appended at the end of the page (later in the cascade wins ties; use !important to override JS-written inline variables)',
+  settingsCustomCssPlaceholder: '/* e.g. reserve 36px for a shell with a custom-drawn title bar */\nhtml[data-dsh-title-bar-height="36"] {\n  --dsh-title-bar-strip: 36px !important;\n}',
   settingsSaveFailed: 'Failed to save',
   settingsConflict: 'The setting changed in another window — please retry',
   binaryNoPreview: 'This file type cannot be previewed',
diff --git a/src/client/prefs.ts b/src/client/prefs.ts
index f172fb6..02f33a2 100644
--- a/src/client/prefs.ts
+++ b/src/client/prefs.ts
@@ -14,11 +14,21 @@ import {
   clampTitleBarStrip,
   clampWidthPercent,
   SIDEBAR_PREFS_DEFAULTS,
+  TITLE_BAR_SCHEMES,
+  TITLE_BAR_STRIP_DEFAULT,
   type SidebarPrefs,
+  type TitleBarScheme,
 } from '../prefs-shared.ts'
 
-export { SIDEBAR_PREFS_DEFAULTS, clampTerminalFontSize, clampTitleBarStrip, clampWidthPercent }
-export type { SidebarPrefs }
+export {
+  SIDEBAR_PREFS_DEFAULTS,
+  TITLE_BAR_SCHEMES,
+  TITLE_BAR_STRIP_DEFAULT,
+  clampTerminalFontSize,
+  clampTitleBarStrip,
+  clampWidthPercent,
+}
+export type { SidebarPrefs, TitleBarScheme }
 
 /** The settings wire face the preferences need (a subset of the plugin api). */
 export type SidebarSettingsClient = Pick<typeof api, 'settingsGet' | 'settingsUpdate'>
@@ -69,6 +79,22 @@ export function parsePrefs(value: unknown): SidebarPrefs {
     editorExplorer: typeof record.editorExplorer === 'boolean'
       ? record.editorExplorer
       : SIDEBAR_PREFS_DEFAULTS.editorExplorer,
+    // The title-bar scheme (auto | web | preset | custom). The schema
+    // declares the field WITHOUT a default, so documents written by older
+    // plugin versions resolve without it — migrate from the legacy fields:
+    // a document that ALREADY HAS VALUES (the manual compat flag on, or a
+    // non-default strip px — both only reachable through the old gear
+    // popup) maps to the `custom` scheme so the user's numbers keep
+    // working; a pristine document keeps the conservative `auto` scheme.
+    titleBarScheme: isTitleBarScheme(record.titleBarScheme)
+      ? record.titleBarScheme
+      : (record.titleBarCompat === true || hasLegacyStripValue(record.titleBarStripPx) ? 'custom' : 'auto'),
+    titleBarPresetId: typeof record.titleBarPresetId === 'string'
+      ? record.titleBarPresetId
+      : SIDEBAR_PREFS_DEFAULTS.titleBarPresetId,
+    customCss: typeof record.customCss === 'string'
+      ? record.customCss
+      : SIDEBAR_PREFS_DEFAULTS.customCss,
     titleBarCompat: typeof record.titleBarCompat === 'boolean'
       ? record.titleBarCompat
       : SIDEBAR_PREFS_DEFAULTS.titleBarCompat,
@@ -130,6 +156,21 @@ function booleanMapOf(value: unknown): Record<string, boolean> {
   return out
 }
 
+/** Type guard for the title-bar scheme union (anything else falls back). */
+function isTitleBarScheme(value: unknown): value is TitleBarScheme {
+  return typeof value === 'string' && (TITLE_BAR_SCHEMES as readonly string[]).includes(value)
+}
+
+/**
+ * Whether the legacy document carries an explicit strip value (only
+ * reachable through the old gear popup): a stored number different from the
+ * default counts as "the user already configured something" and migrates to
+ * the `custom` scheme.
+ */
+function hasLegacyStripValue(value: unknown): boolean {
+  return typeof value === 'number' && Number.isFinite(value) && value !== TITLE_BAR_STRIP_DEFAULT
+}
+
 /**
  * Read the resolved side card preferences through the plugin's settings route.
  * @param settings - the settings wire face (the plugin api by default).
diff --git a/src/client/shell-presets.ts b/src/client/shell-presets.ts
new file mode 100644
index 0000000..52b8ebd
--- /dev/null
+++ b/src/client/shell-presets.ts
@@ -0,0 +1,83 @@
+/**
+ * Built-in desktop-shell presets for the "位置兼容模式" secondary setting
+ * (scheme `preset`). DATA-DRIVEN by design: each shell's adaptation lives
+ * in one entry (strip values / optional CSS), the core applies it through
+ * the SAME generic strip variable and CSS-injection mechanism — adding a
+ * shell is adding data, never a code path.
+ *
+ * Inclusion rule (maintained in AGENTS.md §8): only shells that (a) appear
+ * in this repo's issues/PRs (a user actually hit a problem) and (b) have
+ * 100+ GitHub stars (a real user base). The mechanism is opt-in: auto
+ * detection never applies a preset — the settings badge only SUGGESTS it.
+ */
+import type { DesktopEnv } from './desktop-env.ts'
+
+export interface ShellPreset {
+  /** Stable preset id (persisted in `titleBarPresetId`). */
+  readonly id: string
+  /** User-facing name of the shell. */
+  readonly title: string
+  /** One-line description shown in the settings popup. */
+  readonly desc: string
+  /**
+   * The top strip (px) this shell reserves over web content, per
+   * environment — the fallback used when neither the standard WCO API nor
+   * the `dsh-desktop-titlebar-inset` contract parameter is available.
+   * Return undefined when the shell needs no strip in that environment.
+   * MUST be pure (called during render).
+   */
+  readonly stripFor?: (env: DesktopEnv) => number | undefined
+  /**
+   * Extra CSS applied while the preset is enabled (injected last, after the
+   * plugin's own styles). Targets the plugin's stable data attributes and
+   * shell-declared body/URL markers only — never other shells' class names.
+   * Empty for presets fully covered by the strip variable.
+   */
+  readonly css?: string
+  /**
+   * Whether this shell's marker is currently visible (URL stamps / preload
+   * markers — see desktop-env.ts). Used ONLY for the settings "已检测"
+   * badge; never auto-applies anything. MUST be pure.
+   */
+  readonly detect?: (env: DesktopEnv) => boolean
+}
+
+/**
+ * DeepSeek Harness Desktop (anywhere-labs, Electron, 16k+ stars — the most
+ * reported shell in this repo's issues/PRs). Advanced mode: macOS reserves
+ * a 20px caption row (traffic lights top-left), win32 draws the native
+ * window controls in a ~32px overlay (WCO reports the real height when
+ * available, which the auto scheme already consumes; the 32 is the
+ * no-WCO fallback). Compatibility mode keeps the native frame — nothing.
+ */
+const DSH_DESKTOP: ShellPreset = {
+  id: 'dsh-desktop',
+  title: 'DeepSeek Harness Desktop',
+  desc: 'Electron 高级模式（无边框）：macOS 顶栏 20px、Windows 无 WCO 时 32px 标题栏让位',
+  stripFor: (env) => {
+    if (env.mode !== 'advanced') return undefined
+    if (env.platform === 'darwin') return 20
+    if (env.platform === 'win32') return 32
+    return undefined
+  },
+  detect: (env) => env.mode === 'advanced',
+}
+
+const PRESETS: readonly ShellPreset[] = [
+  DSH_DESKTOP,
+]
+
+/** All built-in shell presets (registration order = settings list order). */
+export function getShellPresets(): readonly ShellPreset[] {
+  return PRESETS
+}
+
+/** One preset by id, or undefined for an unknown/empty id. */
+export function getShellPreset(id: string): ShellPreset | undefined {
+  return PRESETS.find(preset => preset.id === id)
+}
+
+/** The strip the active preset contributes for the given environment. */
+export function presetStripFor(preset: ShellPreset | undefined, env: DesktopEnv): number | undefined {
+  return preset?.stripFor?.(env)
+}
diff --git a/src/client/sidebar.module.css b/src/client/sidebar.module.css
index 3dcb15c..f648d4c 100644
--- a/src/client/sidebar.module.css
+++ b/src/client/sidebar.module.css
@@ -282,6 +282,21 @@ body[data-dsh-sidebar-dragging] .bottomPanel {
   padding-right: 40px;
 }
 
+/* ── Desktop drag-region opt-out ──────────────────────────────────────── */
+
+/* Frameless desktop shells make the top strip of the web content draggable
+   (Electron `-webkit-app-region: drag`); pointer events over that strip are
+   swallowed as window drags unless the interactive element opts out
+   (issues #103/#111). The plugin's viewport-corner chrome must declare
+   `no-drag` itself — some shells (Tauri, older desktop builds, third-party
+   wrappers) have no blanket button rule. The property is a no-op in plain
+   browsers and in shells without drag regions — safe everywhere. */
+.toggleCluster,
+.toggleButton,
+.tabBar {
+  -webkit-app-region: no-drag;
+}
+
 /* ── Position compatibility mode (Windows native title bar) ────────────── */
 
 /* Windows frameless / hidden-title-bar windows draw the native caption
diff --git a/src/client/titlebar-strip.ts b/src/client/titlebar-strip.ts
new file mode 100644
index 0000000..c5aada2
--- /dev/null
+++ b/src/client/titlebar-strip.ts
@@ -0,0 +1,37 @@
+/**
+ * The title-bar strip resolution chain — the ONE place that decides how
+ * many pixels the sidebar yields at the top. Standard signals first, then
+ * the user's chosen scheme; never a per-shell branch:
+ *
+ *   0. `web` scheme — EXPLICIT "DSH official web": never adapt, not even
+ *      standard WCO geometry (the user declares the plain web UI).
+ *   1. Window Controls Overlay real geometry (standard API, authoritative
+ *      when present — even 0, e.g. the overlay is hidden while maximized).
+ *   2. The `dsh-desktop-titlebar-inset` URL contract parameter (a shell
+ *      declares the exact pixels it reserves).
+ *   3. The active shell preset's strip (scheme `preset` — opt-in data).
+ *   4. The legacy manual `titleBarStripPx` (scheme `custom`).
+ *   5. 0 — plain-browser semantics, nothing modified.
+ *
+ * The result drives `--dsh-title-bar-strip` + `body[data-dsh-title-bar-compat]`
+ * exactly like the legacy boolean did; only the VALUE source changed.
+ */
+import type { DesktopEnv } from './desktop-env.ts'
+import type { TitleBarScheme } from '../prefs-shared.ts'
+import type { WcoSnapshot } from './wco.ts'
+import { presetStripFor, type ShellPreset } from './shell-presets.ts'
+
+export function computeTitleBarStrip(
+  env: DesktopEnv,
+  wco: WcoSnapshot,
+  scheme: TitleBarScheme,
+  preset: ShellPreset | undefined,
+  customStripPx: number,
+): number {
+  if (scheme === 'web') return 0
+  if (wco.present) return wco.height
+  if (env.titlebarInset > 0) return env.titlebarInset
+  if (scheme === 'preset') return presetStripFor(preset, env) ?? 0
+  if (scheme === 'custom') return customStripPx
+  return 0
+}
diff --git a/src/client/wco.ts b/src/client/wco.ts
new file mode 100644
index 0000000..00edf34
--- /dev/null
+++ b/src/client/wco.ts
@@ -0,0 +1,120 @@
+/**
+ * Reactive Window Controls Overlay geometry — the STANDARD web mechanism
+ * for frameless Chromium shells that draw the native caption buttons
+ * (minimize / maximize / close) OVER the web content (Electron
+ * `titleBarOverlay` on Windows; issue #257). Feature-detected: absent in
+ * plain browsers, macOS, Tauri etc., where the snapshot stays `NONE` and
+ * the sidebar adapts nothing — this is the conservative "auto" signal.
+ *
+ * The API reports the real titlebar rect (CSS px), which differs between
+ * shells and Electron versions (32 / 36 …), and fires `geometrychange`
+ * when the window maximizes / restores / moves — so the strip must be
+ * reactive, not memoized like the URL stamps.
+ *
+ * Module-level store so the Sidebar shell can subscribe via
+ * `useSyncExternalStore`; `setWcoSourceForTests` swaps the source for unit
+ * tests (no real API exists in jsdom/headless).
+ */
+export interface WcoSource {
+  readonly visible: boolean
+  getTitlebarAreaRect(): { readonly x: number; readonly y: number; readonly width: number; readonly height: number }
+  addEventListener(type: 'geometrychange', listener: () => void): void
+  removeEventListener(type: 'geometrychange', listener: () => void): void
+}
+
+/** The current overlay geometry (present=false = API unavailable). */
+export interface WcoSnapshot {
+  readonly present: boolean
+  readonly height: number
+}
+
+/** Snapshot when the API is unavailable (plain browser / non-overlay shell). */
+export const WCO_NONE: WcoSnapshot = Object.freeze({ present: false, height: 0 })
+
+type Listener = () => void
+
+let source: WcoSource | undefined
+let snapshot: WcoSnapshot = WCO_NONE
+let attached = false
+let sourceListener: (() => void) | undefined
+const listeners = new Set<Listener>()
+
+function read(): WcoSnapshot {
+  if (source === undefined) return WCO_NONE
+  try {
+    // A present-but-NOT-visible API is a PHANTOM: headless Chromium and
+    // macOS builds expose the interface but draw no overlay (empty rect,
+    // visible=false). Only a genuinely visible overlay is authoritative —
+    // otherwise the resolution chain would trust a zero rect and silently
+    // skip the shell's real reserved space.
+    if (source.visible !== true) return { present: false, height: 0 }
+    const rect = source.getTitlebarAreaRect()
+    const height = Math.round(rect.height)
+    return Number.isFinite(height) && height > 0
+      ? { present: true, height }
+      : { present: true, height: 0 }
+  } catch {
+    // A hostile/racy API must never break the layout — treat as absent.
+    return { present: false, height: 0 }
+  }
+}
+
+function onGeometryChange(): void {
+  snapshot = read()
+  emit()
+}
+
+function emit(): void {
+  for (const listener of listeners) listener()
+}
+
+/** Attach the native geometrychange listener (once). */
+function attach(): void {
+  if (attached) return
+  attached = true
+  // The test hook may have installed a source already; otherwise attach to
+  // the real navigator API (absent in plain browsers → stay NONE).
+  const candidate = source ?? (navigator as unknown as { windowControlsOverlay?: WcoSource }).windowControlsOverlay
+  if (candidate === undefined) return
+  source = candidate
+  sourceListener = onGeometryChange
+  snapshot = read()
+  source.addEventListener('geometrychange', sourceListener)
+}
+
+/** Detach the native listener (last subscriber left or source swapped). */
+function detach(): void {
+  if (source !== undefined && sourceListener !== undefined) {
+    source.removeEventListener('geometrychange', sourceListener)
+  }
+  sourceListener = undefined
+  attached = false
+}
+
+/** Read the current snapshot (returns the frozen NONE when unavailable). */
+export function getWcoSnapshot(): WcoSnapshot {
+  return snapshot
+}
+
+/**
+ * Subscribe to overlay geometry changes. Attaches to the real
+ * `navigator.windowControlsOverlay` on first subscribe; the disposer
+ * detaches the native listener when the last subscriber leaves.
+ */
+export function subscribeWco(onChange: Listener): () => void {
+  listeners.add(onChange)
+  attach()
+  return () => {
+    listeners.delete(onChange)
+    if (listeners.size === 0) detach()
+  }
+}
+
+/** Test hook: swap the geometry source (undefined = API unavailable). */
+export function setWcoSourceForTests(next: WcoSource | undefined): void {
+  detach()
+  source = next
+  snapshot = next === undefined ? WCO_NONE : read()
+  if (next !== undefined && listeners.size > 0) attach()
+  emit()
+}
diff --git a/src/config.ts b/src/config.ts
index 4af0d03..5f4cae0 100644
--- a/src/config.ts
+++ b/src/config.ts
@@ -129,6 +129,9 @@ export const PrefsSchema: z<SidebarPrefs> = z.object({
   editorExplorer: z.boolean().default(false),
   terminalShell: z.string().default(''),
   terminalShellArgs: z.string().default(''),
+  titleBarScheme: z.union([z.const('auto'), z.const('web'), z.const('preset'), z.const('custom')]),
+  titleBarPresetId: z.string(),
+  customCss: z.string(),
   titleBarCompat: z.boolean().default(false),
   titleBarStripPx: z.number().step(1).min(TITLE_BAR_STRIP_MIN).max(TITLE_BAR_STRIP_MAX).default(TITLE_BAR_STRIP_DEFAULT),
   htmlViewerNoSandbox: z.boolean().default(false),
diff --git a/src/prefs-shared.ts b/src/prefs-shared.ts
index a9f5514..027998d 100644
--- a/src/prefs-shared.ts
+++ b/src/prefs-shared.ts
@@ -85,17 +85,43 @@ export interface SidebarPrefs {
    */
   terminalShellArgs: string
   /**
-   * Position compatibility mode: reserves space at the top for the native
-   * Windows title bar (drawn at the window's top-right corner over the web
-   * content in frameless/hidden-title-bar windows). When on, the toggle
-   * cluster drops below the strip and the right panel's content starts
-   * below it. Off by default — the sidebar layout is untouched.
+   * Title-bar / shell compatibility scheme (the "位置兼容模式" setting):
+   * - `auto` (default): CONSERVATIVE — only the standard Window Controls
+   *   Overlay API (present in frameless Chromium shells that draw the
+   *   native caption buttons over web content) contributes real geometry;
+   *   without it nothing is modified, so plain-browser (web) behavior is
+   *   untouched.
+   * - `web`: EXPLICIT "DSH official web" — never adapt, not even WCO
+   *   geometry (the user declares they run the plain web UI).
+   * - `preset`: apply the built-in shell preset named by
+   *   `titleBarPresetId` (data-driven, opt-in — see shell-presets.ts).
+   * - `custom`: apply the free-form `customCss` (and the legacy
+   *   `titleBarStripPx` strip).
+   */
+  titleBarScheme: TitleBarScheme
+  /**
+   * The built-in shell preset id applied while `titleBarScheme` is
+   * `preset` ('' = no preset — nothing extra is applied).
+   */
+  titleBarPresetId: string
+  /**
+   * Free-form CSS injected into the page (last in the cascade, so it can
+   * override the plugin's styles; use `!important` to override JS-written
+   * inline CSS variables). Applied while `titleBarScheme` is `custom`.
+   */
+  customCss: string
+  /**
+   * LEGACY (kept for read-migration and downgrade mirroring only): position
+   * compatibility mode flag. The UI writes `titleBarScheme` instead; a
+   * stored `true` without a scheme migrates to the `custom` scheme (with
+   * `titleBarStripPx` preserved).
    */
   titleBarCompat: boolean
   /**
-   * The reserved top strip height in px when `titleBarCompat` is on
-   * (0–120, default 40). Drives the `--dsh-title-bar-strip` CSS variable:
-   * the toggle cluster drops `strip + 3px` and the right panel's content
+   * LEGACY (kept for read-migration and downgrade mirroring only): the
+   * reserved top strip height in px used by the `custom` scheme (0–120,
+   * default 40). Drives the `--dsh-title-bar-strip` CSS variable: the
+   * toggle cluster drops `strip + 3px` and the right panel's content
    * starts `strip` px below its top edge.
    */
   titleBarStripPx: number
@@ -192,6 +218,10 @@ export const TITLE_BAR_STRIP_MIN = 0
 export const TITLE_BAR_STRIP_MAX = 120
 export const TITLE_BAR_STRIP_DEFAULT = 40
 
+/** The title-bar / shell compatibility schemes (see {@link SidebarPrefs.titleBarScheme}). */
+export const TITLE_BAR_SCHEMES = ['auto', 'web', 'preset', 'custom'] as const
+export type TitleBarScheme = typeof TITLE_BAR_SCHEMES[number]
+
 /** Fallback prefs used whenever the settings document is unreachable or malformed. */
 export const SIDEBAR_PREFS_DEFAULTS: SidebarPrefs = {
   openByDefault: false,
@@ -206,6 +236,9 @@ export const SIDEBAR_PREFS_DEFAULTS: SidebarPrefs = {
   editorExplorer: false,
   terminalShell: '',
   terminalShellArgs: '',
+  titleBarScheme: 'auto',
+  titleBarPresetId: '',
+  customCss: '',
   titleBarCompat: false,
   titleBarStripPx: TITLE_BAR_STRIP_DEFAULT,
   htmlViewerNoSandbox: false,
diff --git a/tests/desktop-env.spec.ts b/tests/desktop-env.spec.ts
index 87bfe61..53ca36e 100644
--- a/tests/desktop-env.spec.ts
+++ b/tests/desktop-env.spec.ts
@@ -1,7 +1,10 @@
 /**
  * Desktop-shell detection tests: URL stamps (dsh-desktop-mode/platform)
  * from the official Electron shell, the preload marker
- * (__DSH_DESKTOP_FILE_PATH__), and the win32 advanced overlay adaptation.
+ * (__DSH_DESKTOP_FILE_PATH__), and the `dsh-desktop-titlebar-inset`
+ * contract parameter. Geometry ADAPTATION is deliberately NOT here — the
+ * strip resolution chain lives in titlebar-strip.ts (standard WCO first,
+ * see wco.spec.ts), keeping this module a pure environment reporter.
  */
 import { beforeEach, describe, expect, it } from 'vitest'
 import './browser-globals.ts'
@@ -18,25 +21,25 @@ beforeEach(() => {
 })
 
 describe('parseDesktopEnv', () => {
-  it('reports a plain browser page as non-desktop', () => {
-    expect(parseDesktopEnv()).toEqual({ desktop: false, mode: null, platform: null, win32OverlayTop: 0 })
+  it('reports a plain browser page as non-desktop with no inset', () => {
+    expect(parseDesktopEnv()).toEqual({ desktop: false, mode: null, platform: null, titlebarInset: 0 })
   })
 
-  it('parses win32 advanced stamps with the 32px window-control overlay', () => {
+  it('parses win32 advanced stamps (no overlay guess — geometry comes from WCO/preset)', () => {
     setSearch('?dsh-desktop-mode=advanced&dsh-desktop-platform=win32')
     const env = parseDesktopEnv()
     expect(env.desktop).toBe(true)
     expect(env.mode).toBe('advanced')
     expect(env.platform).toBe('win32')
-    expect(env.win32OverlayTop).toBe(32)
+    expect(env.titlebarInset).toBe(0)
   })
 
-  it('parses darwin advanced stamps without an overlay (traffic lights are top-left)', () => {
+  it('parses darwin advanced stamps', () => {
     setSearch('?dsh-desktop-mode=advanced&dsh-desktop-platform=darwin')
     const env = parseDesktopEnv()
     expect(env.desktop).toBe(true)
     expect(env.platform).toBe('darwin')
-    expect(env.win32OverlayTop).toBe(0)
+    expect(env.titlebarInset).toBe(0)
   })
 
   it('parses compatibility mode as desktop with the native frame (no adaptation)', () => {
@@ -44,7 +47,7 @@ describe('parseDesktopEnv', () => {
     const env = parseDesktopEnv()
     expect(env.desktop).toBe(true)
     expect(env.mode).toBe('compatibility')
-    expect(env.win32OverlayTop).toBe(0)
+    expect(env.titlebarInset).toBe(0)
   })
 
   it('detects the desktop preload marker even without URL stamps', () => {
@@ -52,7 +55,7 @@ describe('parseDesktopEnv', () => {
     const env = parseDesktopEnv()
     expect(env.desktop).toBe(true)
     expect(env.mode).toBeNull()
-    expect(env.win32OverlayTop).toBe(0)
+    expect(env.titlebarInset).toBe(0)
   })
 
   it('ignores unknown mode values (exotic shells keep plain-browser semantics)', () => {
@@ -61,6 +64,20 @@ describe('parseDesktopEnv', () => {
     expect(parseDesktopEnv().desktop).toBe(false)
   })
 
+  it('reads the documented titlebar-inset contract parameter (clamped 0–120)', () => {
+    setSearch('?dsh-desktop-mode=advanced&dsh-desktop-platform=win32&dsh-desktop-titlebar-inset=36')
+    expect(parseDesktopEnv().titlebarInset).toBe(36)
+    setSearch('?dsh-desktop-mode=advanced&dsh-desktop-titlebar-inset=200')
+    resetDesktopEnvForTests()
+    expect(parseDesktopEnv().titlebarInset).toBe(120)
+    setSearch('?dsh-desktop-mode=advanced&dsh-desktop-titlebar-inset=-5')
+    resetDesktopEnvForTests()
+    expect(parseDesktopEnv().titlebarInset).toBe(0)
+    setSearch('?dsh-desktop-mode=advanced&dsh-desktop-titlebar-inset=abc')
+    resetDesktopEnvForTests()
+    expect(parseDesktopEnv().titlebarInset).toBe(0)
+  })
+
   it('memoizes across calls until the test hook resets', () => {
     setSearch('?dsh-desktop-mode=advanced&dsh-desktop-platform=win32')
     const first = parseDesktopEnv()
diff --git a/tests/e2e/drag-layout.e2e.ts b/tests/e2e/drag-layout.e2e.ts
index 01d57bf..32db2c6 100644
--- a/tests/e2e/drag-layout.e2e.ts
+++ b/tests/e2e/drag-layout.e2e.ts
@@ -702,3 +702,34 @@ test('bottom panel never flashes full-width after a width drag release (issue #2
     ).toBeLessThanOrEqual(8)
   }
 })
+
+test('the bottom-push anchor resolves through the composite selectors (at least one; same element when both)', async ({ page }) => {
+  // layout.css pushes the bottom panel via the center column. The selector
+  // is COMPOSITE on purpose: `[data-pane="conversation"]` (0.1.x naming)
+  // and `:has(> [data-slot="conversation"])` (rc.8-era naming) — HOST
+  // VERSIONS MAY RENAME THE ATTRIBUTE (issue #208 comment / PR #226), so
+  // the contract is "at least one resolves", and when both resolve they
+  // must hit the SAME element (otherwise the push would land twice).
+  await page.goto(BASE_URL, { waitUntil: 'domcontentloaded' })
+  await expect(page.locator('[data-dsh-better-sidebar]')).toBeAttached({ timeout: 90_000 })
+  const anchors = await page.evaluate(() => {
+    const a = document.querySelector('#root [data-dsh-frame] > [data-pane="conversation"]')
+    const b = document.querySelector('#root :has(> [data-slot="conversation"])')
+    const frame = document.querySelector('#root [data-dsh-frame]')
+    return {
+      a: a !== null,
+      b: b !== null,
+      same: a !== null && b !== null && a === b,
+      frameChildren: frame !== null
+        ? [...frame.children].map(el => `${el.tagName}[${[...el.attributes].map(attr => attr.name).filter(name => name.startsWith('data-')).join(',')}]`)
+        : [],
+    }
+  })
+  expect(
+    anchors.a || anchors.b,
+    `at least one bottom-push anchor must resolve on this host (frame children: ${anchors.frameChildren.join(' / ') || 'no [data-dsh-frame]'})`,
+  ).toBe(true)
+  if (anchors.a && anchors.b) {
+    expect(anchors.same, 'both selectors must hit the SAME center-column element').toBe(true)
+  }
+})
diff --git a/tests/e2e/mount.e2e.ts b/tests/e2e/mount.e2e.ts
index a7dbf2c..7e038ce 100644
--- a/tests/e2e/mount.e2e.ts
+++ b/tests/e2e/mount.e2e.ts
@@ -341,20 +341,122 @@ test('plugin mounts into the DSH shell and survives a built-in tab sweep', async
   await page.screenshot({ path: 'test-results/mount-final.png' })
 })
 
-test('desktop shell stamps auto-enable the win32 title-bar compatibility mode', async ({ page }) => {
+test('conservative auto: URL stamps alone never modify the layout; plugin chrome carries the stable data attributes', async ({ page }) => {
   // The official DSH Desktop shell stamps every render URL with
-  // dsh-desktop-mode / dsh-desktop-platform (and exposes a preload marker).
-  // The win32 advanced shell reserves a 32px overlay for the window
-  // controls where the toggle cluster sits — the sidebar must auto-drop
-  // below it (body[data-dsh-title-bar-compat]) without any manual pref.
+  // dsh-desktop-mode / dsh-desktop-platform. Under the conservative AUTO
+  // scheme, shell stamps are REPORTS, not geometry: without the standard
+  // Window Controls Overlay API the layout must stay untouched (plain-web
+  // semantics) — the strip/body attribute appear only for real standard
+  // geometry (see the WCO scenario below) or an opt-in preset.
   await page.goto(`${BASE_URL}?dsh-desktop-mode=advanced&dsh-desktop-platform=win32`, { waitUntil: 'domcontentloaded' })
   await expect(page.locator('[data-dsh-better-sidebar]')).toBeAttached({ timeout: 90_000 })
   await expect(
     page.locator('body[data-dsh-title-bar-compat]'),
-    'win32 advanced shell must auto-enable title-bar compatibility',
-  ).toBeAttached({ timeout: 90_000 })
-  // The strip variable must be sized to the shell's 32px overlay.
+    'stamps alone must NOT auto-enable title-bar compatibility under auto',
+  ).toHaveCount(0)
   await expect
     .poll(() => page.evaluate(() => document.documentElement.style.getPropertyValue('--dsh-title-bar-strip')))
-    .toBe('32px')
+    .toBe('')
+  // The stable addressing surface for presets / custom CSS is mounted.
+  await expect(page.locator('[data-dsh-toggle-cluster]')).toBeAttached()
+  await expect(page.locator('[data-dsh-panel]').first()).toBeAttached()
+  // The plugin's interactive chrome opts out of Electron drag regions
+  // (issues #103/#111) — inert in plain browsers, present in the bundle
+  // (the bundler minifies the property's whitespace, so match loosely).
+  const hasNoDragRule = await page.evaluate(() => {
+    for (const tag of document.querySelectorAll('style')) {
+      if (tag.textContent !== null && /-webkit-app-region:\s*no-drag/.test(tag.textContent)) return true
+    }
+    return false
+  })
+  expect(hasNoDragRule, 'the bundle must ship the drag-region opt-out rule').toBe(true)
+})
+
+test('standard WCO geometry drives the strip reactively (issue #257)', async ({ page }) => {
+  // The Window Controls Overlay API is the STANDARD signal for shells that
+  // draw the native caption buttons over web content (Electron
+  // `titleBarOverlay`). Mock it with the real API shape: the strip must
+  // follow the reported rect and react to geometrychange (maximize/restore).
+  await page.addInitScript(() => {
+    const rect = { x: 0, y: 0, width: 138, height: 36 }
+    const listeners = new Set<() => void>()
+    Object.defineProperty(navigator, 'windowControlsOverlay', {
+      configurable: true,
+      value: {
+        visible: true,
+        getTitlebarAreaRect: () => ({ ...rect }),
+        addEventListener: (type: string, listener: () => void) => { if (type === 'geometrychange') listeners.add(listener) },
+        removeEventListener: (type: string, listener: () => void) => { if (type === 'geometrychange') listeners.delete(listener) },
+      },
+    })
+    ;(globalThis as { __wcoMock?: { setHeight: (height: number) => void } }).__wcoMock = {
+      setHeight: (height: number) => {
+        rect.height = height
+        for (const listener of listeners) listener()
+      },
+    }
+  })
+  await page.goto(BASE_URL, { waitUntil: 'domcontentloaded' })
+  await expect(page.locator('[data-dsh-better-sidebar]')).toBeAttached({ timeout: 90_000 })
+  // Real reported height (36px, not a hardcoded 32) drives the strip.
+  await expect(page.locator('body[data-dsh-title-bar-compat]')).toBeAttached({ timeout: 90_000 })
+  await expect
+    .poll(() => page.evaluate(() => document.documentElement.style.getPropertyValue('--dsh-title-bar-strip')))
+    .toBe('36px')
+  // Maximize → the overlay reports a zero rect → the strip is removed.
+  await page.evaluate(() => (globalThis as { __wcoMock?: { setHeight: (height: number) => void } }).__wcoMock?.setHeight(0))
+  await expect(page.locator('body[data-dsh-title-bar-compat]')).toHaveCount(0)
+  await expect
+    .poll(() => page.evaluate(() => document.documentElement.style.getPropertyValue('--dsh-title-bar-strip')))
+    .toBe('')
+  // Restore → the strip comes back.
+  await page.evaluate(() => (globalThis as { __wcoMock?: { setHeight: (height: number) => void } }).__wcoMock?.setHeight(36))
+  await expect(page.locator('body[data-dsh-title-bar-compat]')).toBeAttached()
+})
+
+test('opt-in shell preset applies its strip when WCO is absent (data-driven, manual)', async ({ request, page }) => {
+  // The anywhere-labs DSH Desktop preset (shell-presets.ts) is OPT-IN: under
+  // the preset scheme the win32 advanced stamp resolves to its 32px fallback
+  // even without the WCO API; auto never does this.
+  const update = await request.post(`${BASE_URL}/sidebar/api/settings.update`, {
+    data: { patch: { titleBarScheme: 'preset', titleBarPresetId: 'dsh-desktop', titleBarCompat: true } },
+  })
+  expect(update.ok(), `settings.update: ${update.status()}`).toBe(true)
+  try {
+    await page.goto(`${BASE_URL}?dsh-desktop-mode=advanced&dsh-desktop-platform=win32`, { waitUntil: 'domcontentloaded' })
+    await expect(page.locator('[data-dsh-better-sidebar]')).toBeAttached({ timeout: 90_000 })
+    await expect(page.locator('body[data-dsh-title-bar-compat]')).toBeAttached({ timeout: 90_000 })
+    await expect
+      .poll(() => page.evaluate(() => document.documentElement.style.getPropertyValue('--dsh-title-bar-strip')))
+      .toBe('32px')
+    // The v1 anywhere-labs preset is PURE STRIP DATA (no extra CSS — the
+    // injection mechanism is exercised by the custom-scheme test). Assert
+    // the absence explicitly: a future preset that ADDS css would trip
+    // here instead of silently shipping unstyled.
+    await expect(page.locator('style[data-dsh-preset-css]')).toHaveCount(0)
+  } finally {
+    // Restore the shared server state for the lanes after this one.
+    await request.post(`${BASE_URL}/sidebar/api/settings.update`, {
+      data: { patch: { titleBarScheme: 'auto', titleBarPresetId: '', customCss: '', titleBarCompat: false } },
+    })
+  }
+})
+
+test('custom scheme injects the user stylesheet live', async ({ request, page }) => {
+  const update = await request.post(`${BASE_URL}/sidebar/api/settings.update`, {
+    data: { patch: { titleBarScheme: 'custom', customCss: 'html { --dsh-e2e-marker: 1; }', titleBarCompat: true } },
+  })
+  expect(update.ok(), `settings.update: ${update.status()}`).toBe(true)
+  try {
+    await page.goto(BASE_URL, { waitUntil: 'domcontentloaded' })
+    await expect(page.locator('[data-dsh-better-sidebar]')).toBeAttached({ timeout: 90_000 })
+    await expect(page.locator('style[data-dsh-custom-css="custom"]')).toBeAttached()
+    // The injected CSS is live (a custom property the page can read back).
+    const marker = await page.evaluate(() => getComputedStyle(document.documentElement).getPropertyValue('--dsh-e2e-marker').trim())
+    expect(marker).toBe('1')
+  } finally {
+    await request.post(`${BASE_URL}/sidebar/api/settings.update`, {
+      data: { patch: { titleBarScheme: 'auto', titleBarPresetId: '', customCss: '', titleBarCompat: false } },
+    })
+  }
 })
diff --git a/tests/plugin-shape.spec.ts b/tests/plugin-shape.spec.ts
index 72f20e3..56f7270 100644
--- a/tests/plugin-shape.spec.ts
+++ b/tests/plugin-shape.spec.ts
@@ -69,8 +69,15 @@ describe('dsh-better-sidebar plugin export shape', () => {
     // and 13px.
     expect(resolved.terminalFontFamily).toBe('')
     expect(resolved.terminalFontSize).toBe(13)
-    // The position-compat mode defaults OFF (the normal layout is default),
-    // with the strip defaulting to 40px.
+    // The position-compat scheme is declared WITHOUT a schema default so a
+    // stored document that predates it resolves without the field — the
+    // CLIENT parsePrefs then applies the conservative `auto` default (or
+    // migrates the legacy boolean), which is exactly what makes old
+    // documents migrate instead of silently flipping to a scheme. The
+    // legacy strip keeps its schema default of 40px.
+    expect(resolved.titleBarScheme).toBeUndefined()
+    expect(resolved.titleBarPresetId).toBeUndefined()
+    expect(resolved.customCss).toBeUndefined()
     expect(resolved.titleBarCompat).toBe(false)
     expect(resolved.titleBarStripPx).toBe(40)
     // The enable-switch maps resolve to {} (everything on) for old documents.
diff --git a/tests/prefs.spec.ts b/tests/prefs.spec.ts
index 45a700c..d1c1920 100644
--- a/tests/prefs.spec.ts
+++ b/tests/prefs.spec.ts
@@ -45,6 +45,9 @@ describe('side card preferences', () => {
         editorExplorer: false,
         terminalShell: '',
         terminalShellArgs: '',
+        titleBarScheme: 'auto',
+        titleBarPresetId: '',
+        customCss: '',
         titleBarCompat: false,
         titleBarStripPx: 40,
         htmlViewerNoSandbox: false,
@@ -74,6 +77,9 @@ describe('side card preferences', () => {
         editorExplorer: false,
         terminalShell: '',
         terminalShellArgs: '',
+        titleBarScheme: 'auto',
+        titleBarPresetId: '',
+        customCss: '',
         titleBarCompat: false,
         titleBarStripPx: 40,
         htmlViewerNoSandbox: false,
@@ -103,6 +109,9 @@ describe('side card preferences', () => {
         editorExplorer: false,
         terminalShell: '',
         terminalShellArgs: '',
+        titleBarScheme: 'auto',
+        titleBarPresetId: '',
+        customCss: '',
         titleBarCompat: false,
         titleBarStripPx: 40,
         htmlViewerNoSandbox: false,
@@ -151,14 +160,42 @@ describe('side card preferences', () => {
     expect((await loadPrefs(wire({ editorExplorer: true }))).editorExplorer).toBe(true)
   })
 
-  it('defaults titleBarCompat to false; only an explicit true turns the position-compat mode on', async () => {
-    // Absent or malformed → off (the normal layout is the default).
-    expect((await loadPrefs(wire({}))).titleBarCompat).toBe(false)
-    expect((await loadPrefs(wire({ titleBarCompat: 'yes' }))).titleBarCompat).toBe(false)
-    expect((await loadPrefs(wire({ titleBarCompat: 1 }))).titleBarCompat).toBe(false)
-    // Explicit booleans survive verbatim.
-    expect((await loadPrefs(wire({ titleBarCompat: false }))).titleBarCompat).toBe(false)
-    expect((await loadPrefs(wire({ titleBarCompat: true }))).titleBarCompat).toBe(true)
+  it('defaults the title-bar scheme to the conservative auto with no preset or custom CSS', async () => {
+    // Absent or malformed → auto (plain web keeps the untouched layout).
+    expect((await loadPrefs(wire({}))).titleBarScheme).toBe('auto')
+    expect((await loadPrefs(wire({ titleBarScheme: 'weird' }))).titleBarScheme).toBe('auto')
+    expect((await loadPrefs(wire({ titleBarScheme: 1 }))).titleBarScheme).toBe('auto')
+    expect((await loadPrefs(wire({}))).titleBarPresetId).toBe('')
+    expect((await loadPrefs(wire({ titleBarPresetId: 5 }))).titleBarPresetId).toBe('')
+    expect((await loadPrefs(wire({}))).customCss).toBe('')
+    expect((await loadPrefs(wire({ customCss: 7 }))).customCss).toBe('')
+    // Valid values survive verbatim (including the explicit web scheme).
+    const picked = await loadPrefs(wire({ titleBarScheme: 'preset', titleBarPresetId: 'dsh-desktop', customCss: 'html { }' }))
+    expect(picked.titleBarScheme).toBe('preset')
+    expect(picked.titleBarPresetId).toBe('dsh-desktop')
+    expect(picked.customCss).toBe('html { }')
+    expect((await loadPrefs(wire({ titleBarScheme: 'web' }))).titleBarScheme).toBe('web')
+  })
+
+  it('migrates LEGACY documents that ALREADY HAVE VALUES into the custom scheme', async () => {
+    // A pre-scheme document with the manual compat flag on maps to the
+    // custom scheme, keeping the strip px the user chose.
+    const migrated = await loadPrefs(wire({ titleBarCompat: true, titleBarStripPx: 56 }))
+    expect(migrated.titleBarScheme).toBe('custom')
+    expect(migrated.titleBarStripPx).toBe(56)
+    // A non-default strip px alone (only reachable through the old gear
+    // popup) also counts as "already has values" → custom.
+    const stripOnly = await loadPrefs(wire({ titleBarStripPx: 48 }))
+    expect(stripOnly.titleBarScheme).toBe('custom')
+    expect(stripOnly.titleBarStripPx).toBe(48)
+    // A stored scheme always wins over the legacy fields (round-trip of the
+    // mirrored write: preset stays preset even though the mirror is true).
+    const roundTrip = await loadPrefs(wire({ titleBarScheme: 'preset', titleBarCompat: true }))
+    expect(roundTrip.titleBarScheme).toBe('preset')
+    // Legacy off / absent / default strip → the conservative auto scheme.
+    expect((await loadPrefs(wire({ titleBarCompat: false }))).titleBarScheme).toBe('auto')
+    expect((await loadPrefs(wire({ titleBarStripPx: 40 }))).titleBarScheme).toBe('auto')
+    expect((await loadPrefs(wire({}))).titleBarScheme).toBe('auto')
   })
 
   it('defaults titleBarStripPx to 40 and clamps stored values into the contract range', async () => {
@@ -223,9 +260,9 @@ 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, bottomPanelAutoTerminal: true, terminalFontFamily: '', terminalFontSize: 13, interceptOpenPath: true, editorExplorer: true, terminalShell: '', terminalShellArgs: '', 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, autoOpenJobs: true, agentTerminalTools: 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, bottomPanelAutoTerminal: true, terminalFontFamily: '', terminalFontSize: 13, interceptOpenPath: true, editorExplorer: true, terminalShell: '', terminalShellArgs: '', 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, autoOpenJobs: true, agentTerminalTools: 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)
@@ -261,7 +298,7 @@ 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, bottomPanelAutoTerminal: true, terminalFontFamily: '', terminalFontSize: 13, interceptOpenPath: true, editorExplorer: true, terminalShell: '', terminalShellArgs: '', 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, autoOpenJobs: true, agentTerminalTools: 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)
@@ -271,7 +308,7 @@ 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, bottomPanelAutoTerminal: true, terminalFontFamily: '', terminalFontSize: 13, interceptOpenPath: true, editorExplorer, terminalShell: '', terminalShellArgs: '', 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, autoOpenJobs: true, agentTerminalTools: 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-${editorExplorer}`)
       const openTabs = allLeaves(openStore.getSnapshot().state!.splits).flatMap(leaf => leaf.tabs)
       expect(openTabs.map(tab => tab.type)).toEqual(['editor'])
@@ -281,7 +318,7 @@ describe('side card preferences', () => {
   it('seeds the empty editor home tab (files window) in both editorExplorer modes', () => {
     for (const editorExplorer of [true, false]) {
       const store = createSidebarStore()
-      store.setPrefs({ openByDefault: true, defaultWidthPercent: 30, autoOpenSubagent: true, autoOpenJobs: true, agentTerminalTools: false, bottomPanelAutoTerminal: true, terminalFontFamily: '', terminalFontSize: 13, interceptOpenPath: true, editorExplorer, terminalShell: '', terminalShellArgs: '', titleBarCompat: false, titleBarStripPx: 40, htmlViewerNoSandbox: false, htmlViewerDefaultUnsafe: false, browserNoSandbox: false, browserInterceptLinks: true, browserInterceptHttp: true, browserInterceptHttps: false, tabsEnabled: {}, viewersEnabled: {}, pluginSettings: {} })
+      store.setPrefs({ openByDefault: true, defaultWidthPercent: 30, autoOpenSubagent: true, autoOpenJobs: true, agentTerminalTools: false, bottomPanelAutoTerminal: true, terminalFontFamily: '', terminalFontSize: 13, interceptOpenPath: true, editorExplorer, terminalShell: '', terminalShellArgs: '', titleBarScheme: 'auto', titleBarPresetId: '', customCss: '', titleBarCompat: false, titleBarStripPx: 40, htmlViewerNoSandbox: false, htmlViewerDefaultUnsafe: false, browserNoSandbox: false, browserInterceptLinks: true, browserInterceptHttp: true, browserInterceptHttps: false, tabsEnabled: {}, viewersEnabled: {}, pluginSettings: {} })
       store.setSession(`fresh-${editorExplorer}`)
       const tabs = allLeaves(store.getSnapshot().state!.splits).flatMap(leaf => leaf.tabs)
       expect(tabs).toHaveLength(1)
diff --git a/tests/shell-presets.spec.ts b/tests/shell-presets.spec.ts
new file mode 100644
index 0000000..a03aa2d
--- /dev/null
+++ b/tests/shell-presets.spec.ts
@@ -0,0 +1,66 @@
+/**
+ * Built-in shell-preset data tests: registry integrity (unique ids, non-empty
+ * titles, pure strip/detect functions) and the anywhere-labs DSH Desktop
+ * entry's strip values (darwin advanced 20px, win32 advanced 32px as the
+ * no-WCO fallback, compatibility/plain browser nothing).
+ */
+import { describe, expect, it } from 'vitest'
+import { getShellPreset, getShellPresets, presetStripFor } from '../src/client/shell-presets.ts'
+import type { DesktopEnv } from '../src/client/desktop-env.ts'
+
+const env = (partial: Partial<DesktopEnv>): DesktopEnv => ({
+  desktop: false,
+  mode: null,
+  platform: null,
+  titlebarInset: 0,
+  ...partial,
+})
+
+describe('shell presets', () => {
+  it('keeps the registry well-formed (unique ids, titles, pure strip functions)', () => {
+    const presets = getShellPresets()
+    expect(presets.length).toBeGreaterThan(0)
+    const ids = new Set<string>()
+    for (const preset of presets) {
+      expect(ids.has(preset.id)).toBe(false)
+      ids.add(preset.id)
+      expect(preset.title.length).toBeGreaterThan(0)
+      expect(preset.desc.length).toBeGreaterThan(0)
+      // The strip function must be total — an unknown environment yields
+      // undefined, never a throw.
+      expect(() => presetStripFor(preset, env({ desktop: false, mode: null, platform: null }))).not.toThrow()
+      expect(() => preset.detect?.(env({ desktop: false, mode: null, platform: null }))).not.toThrow()
+    }
+  })
+
+  it('looks up presets by id; unknown/empty ids resolve to undefined', () => {
+    expect(getShellPreset('dsh-desktop')).toBeDefined()
+    expect(getShellPreset('')).toBeUndefined()
+    expect(getShellPreset('no-such-shell')).toBeUndefined()
+  })
+
+  describe('dsh-desktop (DeepSeek Harness Desktop, anywhere-labs)', () => {
+    const preset = getShellPreset('dsh-desktop')!
+
+    it('reserves 20px on darwin advanced (the caption row above the surfaces)', () => {
+      expect(presetStripFor(preset, env({ desktop: true, mode: 'advanced', platform: 'darwin' }))).toBe(20)
+    })
+
+    it('reserves 32px on win32 advanced as the no-WCO fallback', () => {
+      expect(presetStripFor(preset, env({ desktop: true, mode: 'advanced', platform: 'win32' }))).toBe(32)
+    })
+
+    it('reserves nothing in compatibility mode or on unknown platforms', () => {
+      expect(presetStripFor(preset, env({ desktop: true, mode: 'compatibility', platform: 'win32' }))).toBeUndefined()
+      expect(presetStripFor(preset, env({ desktop: true, mode: 'advanced', platform: 'linux' }))).toBeUndefined()
+      expect(presetStripFor(preset, env({ desktop: false, mode: null, platform: null }))).toBeUndefined()
+    })
+
+    it('detects advanced shells only as a SUGGESTION signal (never auto-applies)', () => {
+      expect(preset.detect?.(env({ desktop: true, mode: 'advanced', platform: 'darwin' }))).toBe(true)
+      expect(preset.detect?.(env({ desktop: true, mode: 'advanced', platform: 'win32' }))).toBe(true)
+      expect(preset.detect?.(env({ desktop: true, mode: 'compatibility', platform: 'win32' }))).toBe(false)
+      expect(preset.detect?.(env({ desktop: false, mode: null, platform: null }))).toBe(false)
+    })
+  })
+})
diff --git a/tests/side-card-section.spec.tsx b/tests/side-card-section.spec.tsx
index 11d2605..4126e2a 100644
--- a/tests/side-card-section.spec.tsx
+++ b/tests/side-card-section.spec.tsx
@@ -125,8 +125,10 @@ describe('SideCardSection declarative inventory', () => {
     const html = renderSection(store, service)
     // Subagents declares a toggle → its card carries the settings gear
     // (aria-label = "<title> Feature settings"); Explorer and Image declare
-    // none → no gear.
+    // none → no gear. The position-compat row is a DROPDOWN (no gear unless
+    // the custom scheme is active), so the total is 1.
     expect(html.match(/aria-label="[^"]*Feature settings"/g)?.length).toBe(1)
+    expect(html).toContain('Subagents Feature settings')
   })
 
   it('renders the two dashed "add plugin" cards (tab grid + viewer grid)', () => {
@@ -159,28 +161,35 @@ describe('SideCardSection declarative inventory', () => {
     const { store, service } = mount()
     store.setPrefs({ ...store.getPrefs(), tabsEnabled: { subagent: false } })
     const html = renderSection(store, service)
+    // The disabled Subagents card loses its gear; the position-compat row
+    // is a dropdown (default auto → no gear either).
     expect(html).not.toContain('Feature settings')
   })
 
-  it('renders the position-compat mode general row: off by default, checked when the pref is on', () => {
+  it('renders the position-compat mode row as a scheme dropdown: auto default, custom keeps the gear', () => {
     const { store, service } = mount()
     let html = renderSection(store, service)
-    // The general row renders its title and description.
+    // The general row renders its title and description; the scheme is the
+    // conservative auto by default and the row is the shared SelectMenu
+    // dropdown (the closed anchor shows the picked option — NOT a native
+    // <select>).
     expect(html).toContain('Position compatibility mode')
-    expect(html).toContain('Reserve space for the native Windows title bar')
-    // Three general rows now: only interceptOpenPath is checked by default
-    // (openByDefault defaults off, the titleBarCompat row starts UNCHECKED) —
-    // the checked checkbox count is 1 while the total checkbox count is 3.
-    expect(html.match(/type="checkbox"/g)?.length).toBe(3)
+    expect(html).toContain('Pick the title-bar compatibility scheme: auto-detect (default, conservative) / DSH official web / known desktop shells / custom (shift distance + custom CSS)')
+    expect(html).not.toContain('<select')
+    expect(html).toContain('>Auto-detect<')
+    // Two general-row switches remain (openByDefault + interceptOpenPath),
+    // only interceptOpenPath checked by default — the scheme row is a
+    // dropdown, not a switch.
+    expect(html.match(/type="checkbox"/g)?.length).toBe(2)
     expect(html.match(/checked=""/g)?.length).toBe(1)
-    // The row's gear (customize the shift distance) is dormant while the
-    // mode is off — the feature-card convention.
+    // Auto (default) needs no further settings → no gear.
     expect(html).not.toContain('Position compatibility mode Feature settings')
 
-    // When the pref is on, the new switch is checked and the gear appears.
-    store.setPrefs({ ...store.getPrefs(), titleBarCompat: true })
+    // The custom scheme keeps its settings button (the px + CSS popup);
+    // the anchor now shows the picked custom option.
+    store.setPrefs({ ...store.getPrefs(), titleBarScheme: 'custom', titleBarCompat: true })
     html = renderSection(store, service)
-    expect(html.match(/checked=""/g)?.length).toBe(2)
+    expect(html).toContain('>Custom<')
     expect(html).toContain('aria-label="Position compatibility mode Feature settings"')
   })
 })
diff --git a/tests/titlebar-strip.spec.ts b/tests/titlebar-strip.spec.ts
new file mode 100644
index 0000000..f7d1a96
--- /dev/null
+++ b/tests/titlebar-strip.spec.ts
@@ -0,0 +1,75 @@
+/**
+ * The title-bar strip resolution chain: standard WCO geometry first
+ * (authoritative even when 0), then the documented URL inset contract
+ * parameter, then the opt-in preset / custom scheme — and 0 (plain web,
+ * nothing modified) otherwise. No per-shell branch lives in the core.
+ */
+import { describe, expect, it } from 'vitest'
+import { computeTitleBarStrip } from '../src/client/titlebar-strip.ts'
+import type { DesktopEnv } from '../src/client/desktop-env.ts'
+import type { WcoSnapshot } from '../src/client/wco.ts'
+import type { ShellPreset } from '../src/client/shell-presets.ts'
+
+const env = (partial: Partial<DesktopEnv>): DesktopEnv => ({
+  desktop: false,
+  mode: null,
+  platform: null,
+  titlebarInset: 0,
+  ...partial,
+})
+
+const wco = (present: boolean, height = 0): WcoSnapshot => ({ present, height })
+
+const noPreset: ShellPreset | undefined = undefined
+
+describe('computeTitleBarStrip', () => {
+  it('keeps plain web untouched: no WCO, no inset, no scheme → 0', () => {
+    expect(computeTitleBarStrip(env({}), wco(false), 'auto', noPreset, 40)).toBe(0)
+    expect(computeTitleBarStrip(env({}), wco(false), 'custom', noPreset, 40)).toBe(40)
+  })
+
+  it('the explicit WEB scheme forces 0 — not even standard WCO geometry applies', () => {
+    const desktop = env({ desktop: true, mode: 'advanced', platform: 'win32' })
+    // The user declared "DSH official web": no adaptation at all, even when
+    // a real overlay exists or a preset is active.
+    expect(computeTitleBarStrip(desktop, wco(true, 36), 'web', noPreset, 40)).toBe(0)
+    expect(computeTitleBarStrip(desktop, wco(false), 'web', noPreset, 40)).toBe(0)
+    expect(computeTitleBarStrip(desktop, wco(false), 'web', {
+      id: 't', title: 't', desc: '', stripFor: () => 20,
+    }, 40)).toBe(0)
+  })
+
+  it('trusts the standard WCO geometry first in every scheme (even 0 — e.g. maximized)', () => {
+    const desktop = env({ desktop: true, mode: 'advanced', platform: 'win32' })
+    expect(computeTitleBarStrip(desktop, wco(true, 36), 'auto', noPreset, 0)).toBe(36)
+    expect(computeTitleBarStrip(desktop, wco(true, 36), 'preset', noPreset, 0)).toBe(36)
+    expect(computeTitleBarStrip(desktop, wco(true, 36), 'custom', noPreset, 40)).toBe(36)
+    // Authoritative zero: the overlay is hidden while maximized — no strip.
+    expect(computeTitleBarStrip(desktop, wco(true, 0), 'auto', noPreset, 40)).toBe(0)
+  })
+
+  it('applies the documented URL inset contract parameter before any scheme', () => {
+    const stamped = env({ desktop: true, mode: 'advanced', platform: 'darwin', titlebarInset: 20 })
+    expect(computeTitleBarStrip(stamped, wco(false), 'auto', noPreset, 0)).toBe(20)
+    expect(computeTitleBarStrip(stamped, wco(false), 'preset', noPreset, 0)).toBe(20)
+  })
+
+  it('uses the opt-in preset strip under the preset scheme only', () => {
+    const preset: ShellPreset = {
+      id: 't', title: 't', desc: '',
+      stripFor: (e) => e.platform === 'darwin' ? 20 : undefined,
+    }
+    const darwin = env({ desktop: true, mode: 'advanced', platform: 'darwin' })
+    expect(computeTitleBarStrip(darwin, wco(false), 'preset', preset, 0)).toBe(20)
+    // Auto never applies the preset — only standard signals.
+    expect(computeTitleBarStrip(darwin, wco(false), 'auto', preset, 0)).toBe(0)
+    // Custom never applies the preset either.
+    expect(computeTitleBarStrip(darwin, wco(false), 'custom', preset, 0)).toBe(0)
+  })
+
+  it('uses the manual strip px under the custom scheme only', () => {
+    expect(computeTitleBarStrip(env({}), wco(false), 'custom', noPreset, 56)).toBe(56)
+    expect(computeTitleBarStrip(env({}), wco(false), 'auto', noPreset, 56)).toBe(0)
+    expect(computeTitleBarStrip(env({}), wco(false), 'preset', noPreset, 56)).toBe(0)
+  })
+})
diff --git a/tests/wco.spec.ts b/tests/wco.spec.ts
new file mode 100644
index 0000000..bc7f737
--- /dev/null
+++ b/tests/wco.spec.ts
@@ -0,0 +1,125 @@
+/**
+ * Window Controls Overlay (WCO) geometry store tests: feature detection,
+ * subscribe/getSnapshot, geometrychange re-reads, and the absent-API
+ * fallback (the conservative "auto" signal — plain browsers and non-overlay
+ * shells report NONE and the sidebar adapts nothing).
+ */
+import { afterEach, beforeEach, describe, expect, it } from 'vitest'
+import './browser-globals.ts'
+import {
+  getWcoSnapshot, setWcoSourceForTests, subscribeWco, WCO_NONE,
+  type WcoSource,
+} from '../src/client/wco.ts'
+
+/** A controllable fake of the standard API surface. */
+function makeSource(initial: { width: number; height: number; visible?: boolean }): {
+  source: WcoSource
+  setRect: (width: number, height: number) => void
+  fireGeometryChange: () => void
+  listeners: Set<() => void>
+} {
+  const listeners = new Set<() => void>()
+  let rect = { x: 0, y: 0, width: initial.width, height: initial.height }
+  const source: WcoSource = {
+    visible: initial.visible ?? true,
+    getTitlebarAreaRect: () => rect,
+    addEventListener: (type, listener) => { if (type === 'geometrychange') listeners.add(listener) },
+    removeEventListener: (type, listener) => { if (type === 'geometrychange') listeners.delete(listener) },
+  }
+  return {
+    source,
+    setRect: (width, height) => { rect = { x: 0, y: 0, width, height } },
+    fireGeometryChange: () => { for (const listener of listeners) listener() },
+    listeners,
+  }
+}
+
+beforeEach(() => {
+  setWcoSourceForTests(undefined)
+})
+
+afterEach(() => {
+  setWcoSourceForTests(undefined)
+})
+
+describe('wco geometry store', () => {
+  it('reports NONE (absent API) in plain browsers / non-overlay shells', () => {
+    expect(getWcoSnapshot()).toBe(WCO_NONE)
+    expect(getWcoSnapshot().present).toBe(false)
+    expect(getWcoSnapshot().height).toBe(0)
+  })
+
+  it('reads the real overlay rect once a source is present', () => {
+    const { source } = makeSource({ width: 138, height: 36 })
+    setWcoSourceForTests(source)
+    expect(getWcoSnapshot()).toEqual({ present: true, height: 36 })
+  })
+
+  it('rounds fractional overlay heights to whole pixels', () => {
+    const { source } = makeSource({ width: 100, height: 35.6 })
+    setWcoSourceForTests(source)
+    expect(getWcoSnapshot().height).toBe(36)
+  })
+
+  it('re-reads geometry on geometrychange (maximize/restore) and notifies subscribers', () => {
+    const { source, setRect, fireGeometryChange, listeners } = makeSource({ width: 138, height: 32 })
+    setWcoSourceForTests(source)
+    const calls: number[] = []
+    const off = subscribeWco(() => { calls.push(getWcoSnapshot().height) })
+    // Maximized: the overlay reports a zero/empty rect.
+    setRect(0, 0)
+    fireGeometryChange()
+    expect(getWcoSnapshot()).toEqual({ present: true, height: 0 })
+    expect(calls).toEqual([0])
+    // Restored.
+    setRect(138, 36)
+    fireGeometryChange()
+    expect(getWcoSnapshot()).toEqual({ present: true, height: 36 })
+    expect(calls).toEqual([0, 36])
+    // The disposer stops notifications.
+    off()
+    setRect(138, 40)
+    fireGeometryChange()
+    expect(calls).toEqual([0, 36])
+    expect(listeners.size).toBe(0)
+  })
+
+  it('treats a PHANTOM API (present but not visible) as absent — headless/macOS expose the interface with no overlay', () => {
+    const { source } = makeSource({ width: 0, height: 0, visible: false })
+    setWcoSourceForTests(source)
+    // present=false lets the strip chain fall through to the inset / preset
+    // / custom scheme instead of trusting an empty rect.
+    expect(getWcoSnapshot()).toEqual({ present: false, height: 0 })
+    // A real overlay flips to authoritative immediately.
+    const real = makeSource({ width: 138, height: 36, visible: true })
+    setWcoSourceForTests(real.source)
+    expect(getWcoSnapshot()).toEqual({ present: true, height: 36 })
+  })
+
+  it('treats a throwing API as absent (never breaks the layout)', () => {
+    const source: WcoSource = {
+      visible: true,
+      getTitlebarAreaRect: () => { throw new Error('racy API') },
+      addEventListener: () => {},
+      removeEventListener: () => {},
+    }
+    setWcoSourceForTests(source)
+    expect(getWcoSnapshot()).toEqual({ present: false, height: 0 })
+  })
+
+  it('re-attaches cleanly when the source is swapped (test hook)', () => {
+    const first = makeSource({ width: 138, height: 32 })
+    const second = makeSource({ width: 138, height: 36 })
+    setWcoSourceForTests(first.source)
+    expect(first.listeners.size).toBe(0) // no subscriber yet
+    const off = subscribeWco(() => {})
+    expect(first.listeners.size).toBe(1)
+    setWcoSourceForTests(second.source)
+    expect(first.listeners.size).toBe(0)
+    expect(second.listeners.size).toBe(1)
+    expect(getWcoSnapshot().height).toBe(36)
+    off()
+    setWcoSourceForTests(undefined)
+    expect(getWcoSnapshot()).toBe(WCO_NONE)
+  })
+})