diff --git a/docs/external-plugin-guide.md b/docs/external-plugin-guide.md
index bf9dcf9..0c45e8f 100644
--- a/docs/external-plugin-guide.md
+++ b/docs/external-plugin-guide.md
@@ -997,7 +997,7 @@ interface SettingsDescriptor {
   - **迁移**：`titleBarScheme` 无默认值；旧文档已有值（`titleBarCompat === true` 或 `titleBarStripPx` 非 40）→ 迁 `custom`；干净文档 → `auto`。
   - **用户空间 CSS**：预设/自定义 css 注入 `<style data-dsh-preset-css|data-dsh-custom-css>` 到 head 末尾（后写胜出；覆盖 JS 内联需 `!important`），fiber 卸载即移除。稳定寻址面：`[data-dsh-toggle-cluster]` / `[data-dsh-panel]` / `[data-dsh-bottom-panel]`。
   - **拖拽区退出**：交互 chrome（`.toggleCluster` / `.toggleButton` / `.tabBar`）统一 `-webkit-app-region: no-drag`（无边框壳拖拽带吞点击，#103/#111）。
-  - **拖拽区退出（视口层）**：宿主把每个**直挂 body 的子元素**都设成 `no-drag`（`html[data-platform=darwin] body > :not(#root)`，选择器含 id，只能靠 `!important` 压过），而 app-region **无视 `pointer-events`**——铺满视口的插件层因此会把它下面的每条 `[data-window-drag]` 拖拽带一起抵消（窗口拖一次就失效，同时丢掉 macOS 双击标题栏缩放，issue #772）。契约：装饰性的视口层用**中性值** `-webkit-app-region: initial !important` 退出计算（`initial` 的计算值 `none` 不扣减拖拽区），层内的面板/控件再声明 `no-drag` 保住点击；当前覆盖 `[data-dsh-better-sidebar]`、`[data-dsh-panel-host]`（`> *` 保持 `no-drag`）与 `.mermaidModal`（放大视图是第二个铺满视口的 body 直挂层）。**交互弹层（`.selectionPopup` 是 `<button>`，`FloatingWindow` / `AnchoredPopover` 自带指针拖拽）不要加 `initial`**：宿主 `:is(button, a, input, …)` 已给它们 `no-drag`，反过来声明 `initial !important` 会让按下变成拖窗（重演 #103/#111）。形状由 `tests/panel-host-css.spec.ts` 在 Linux 的 `pnpm test` 里守护（无 macOS runner），真实级联由挂载 lane 的探针按宿主两条规则逐字复现后断言计算值。
+  - **拖拽区退出（视口层）**：宿主把每个**直挂 body 的子元素**都设成 `no-drag`（`html[data-platform=darwin] body > :not(#root)`，选择器含 id，只能靠 `!important` 压过），而 app-region **无视 `pointer-events`**——插件宿主就是这样一个 body 子元素，在 Electron 里该值还会传到它内部的**铺满视口的面板层**（#772 的 CDP 实测；挂载 lane 用的浏览器引擎不传播该属性，所以面板层自己也声明了同一条规则），于是它把下面每条 `[data-window-drag]` 拖拽带一起抵消（窗口拖一次就失效，同时丢掉 macOS 双击标题栏缩放，issue #772）。契约：装饰性的视口层用**中性值** `-webkit-app-region: initial !important` 退出计算（`initial` 的计算值 `none` 不扣减拖拽区；注意**字面量 `none` 不是中性值**——它计算成 `no-drag`，是扣减值），层内的面板/控件再声明 `no-drag` 保住点击；当前覆盖 `[data-dsh-better-sidebar]`、`[data-dsh-panel-host]`（`> *` 保持 `no-drag`）与 `.mermaidModal`（放大视图是第二个**持久**铺满视口的 body 直挂层）。**交互弹层不要加 `initial`**（`.selectionPopup` 是 `<button>`，`FloatingWindow` / `AnchoredPopover` 自带指针拖拽、不是遮罩层）：宿主 `:is(button, a, input, …)` 已给它们 `no-drag`，反过来声明 `initial !important` 会让按下变成拖窗（重演 #103/#111）。放大视图是**遮罩层例外**——它是模态，只有其中的控件必须保持 `no-drag`；代价是它覆盖在顶部拖拽带上时，点背景会变成拖窗而不是关闭（为「放大图时窗口仍可拖」付的账）。**未纳入**：`FileTree` 的 `.uploadDropChatHint` 同样是 body 直挂的装饰层，但它只在 OS 文件拖拽悬停期间存在且 `pointer-events: none`，收益极小、暂不处理（`FloatingWindow` / `AnchoredPopover` 是交互层，按上面的判据本就该保持 `no-drag`）。形状由 `tests/panel-host-css.spec.ts` 在 Linux 的 `pnpm test` 里守护（无 macOS runner；`tests/theme.spec.ts` 只守颜色，故本轮不涉及），真实级联由挂载 lane 的探针按宿主规则断言计算值（面板宿主探针复现宿主两条 darwin 规则，放大视图探针直接用页面里宿主自己的规则）。
 - **z-index**：面板宿主层 25、按钮簇 45——低于 DSH ui-cordis 插件面板（30）与浮层栈（100/1000+），浮层天然盖住侧边栏。
 
 ### 12.2 注意事项
diff --git a/src/client/sidebar.module.css b/src/client/sidebar.module.css
index 5971e71..6c5f8c8 100644
--- a/src/client/sidebar.module.css
+++ b/src/client/sidebar.module.css
@@ -64,20 +64,28 @@
 }
 
 /* Desktop drag regions ignore pointer-events: the shell's base stylesheet
-   makes every direct body child `no-drag`, and this viewport-sized layer
-   inherited it, cancelling every window-drag strip beneath it once the
-   shell recomputed regions (window drags worked once, then stopped).
-   Take the host and layer out of the app-region computation; `!important`
-   because the shell's `body > :not(#root)` selector outranks ours. The
-   panels themselves stay no-drag so their controls keep receiving clicks.
-   The plugin's OTHER viewport-sized body child — the mermaid zoom modal —
-   carries the same reset on its own rule further down, or opening a diagram
-   would blank window drag (and the macOS double-click-title zoom) while it
-   is up. Deliberately NOT applied to the interactive popups (`.selectionPopup`
-   is a `<button>`; FloatingWindow / AnchoredPopover own pointer drags): the
-   shell's `:is(button, a, input, …)` rule already keeps those no-drag, and
-   `initial !important` would outrank it and start a window drag on press
-   instead — the click-swallow regression of issues #103/#111. */
+   makes every direct body child `no-drag`, and the plugin HOST is one — in
+   Electron that value also reaches the viewport-sized panel layer inside it
+   (#772's CDP reading; the browser engine used by the mount lane does not
+   propagate it, so the layer's own rule below is belt-and-braces), which is
+   what cancelled every window-drag strip beneath it once the shell
+   recomputed regions (window drags worked once, then stopped). Take the host
+   and layer out of the app-region computation; `!important` because the
+   shell's `body > :not(#root)` selector outranks ours. The panels themselves
+   stay no-drag so their controls keep receiving clicks.
+   The plugin's OTHER persistent viewport-sized body child — the mermaid zoom
+   modal — carries the same reset on its own rule further down, or opening a
+   diagram would blank window drag (and the macOS double-click-title zoom)
+   while it is up. It is a modal SCRIM, so it does get the reset even though
+   it is interactive: only its widgets (`<button>` …) need to stay no-drag,
+   and the residual is that its backdrop inside the shell's top drag band
+   starts a window drag instead of closing the modal — the deliberate trade
+   for keeping the window draggable while a diagram is enlarged.
+   Deliberately NOT applied to the other interactive popups (`.selectionPopup`
+   is a `<button>`; FloatingWindow / AnchoredPopover own pointer drags and are
+   not scrims): the shell's `:is(button, a, input, …)` rule already keeps those
+   no-drag, and `initial !important` would outrank it and start a window drag on
+   press instead — the click-swallow regression of issues #103/#111. */
 :global(html[data-platform] body > [data-dsh-better-sidebar]),
 :global([data-dsh-panel-host]) {
   -webkit-app-region: initial !important;
diff --git a/tests/e2e/mount.e2e.ts b/tests/e2e/mount.e2e.ts
index ad72eaa..c232fe1 100644
--- a/tests/e2e/mount.e2e.ts
+++ b/tests/e2e/mount.e2e.ts
@@ -517,6 +517,28 @@ test('plugin mounts into the DSH shell and survives a built-in tab sweep', async
   const modal = page.locator('[data-mermaid-modal]')
   await pane.locator('[data-mermaid-diagram] svg').first().click()
   await expect(modal, 'clicking the diagram must open the zoom modal').toHaveCount(1, { timeout: 10_000 })
+  // While it is up, the modal is the plugin's OTHER viewport-sized BODY CHILD:
+  // without the app-region reset the shell's blanket `body > :not(#root)`
+  // no-drag makes it cancel every window-drag strip (and the macOS
+  // double-click-title zoom) until it closes — issue #772. Measured against the
+  // SHELL's own darwin rules (present in this page's stylesheet, activated by
+  // the platform attribute) rather than a copy: the modal must compute the
+  // neutral `none`, while its toolbar buttons keep `no-drag` so a click on them
+  // is never a window drag.
+  const modalRegions = await page.evaluate(() => {
+    const previous = document.documentElement.dataset.platform
+    document.documentElement.dataset.platform = 'darwin'
+    const modalElement = document.querySelector('[data-mermaid-modal]')
+    const region = (element: Element | null): string => element === null
+      ? 'missing'
+      : getComputedStyle(element).getPropertyValue('-webkit-app-region').trim()
+    const result = { modal: region(modalElement), button: region(modalElement?.querySelector('button') ?? null) }
+    if (previous === undefined) delete document.documentElement.dataset.platform
+    else document.documentElement.dataset.platform = previous
+    return result
+  })
+  expect(modalRegions.modal, 'the zoom modal must opt out of app-region computation').toBe('none')
+  expect(modalRegions.button, 'its buttons must stay no-drag').toBe('no-drag')
   await page.keyboard.press('Escape')
   await expect(modal, 'Esc must close the zoom modal').toHaveCount(0, { timeout: 10_000 })
   await assertNoCrash()
@@ -615,15 +637,17 @@ test('conservative auto: URL stamps alone never modify the layout; plugin chrome
     return false
   })
   expect(hasNoDragRule, 'the bundle must ship the drag-region opt-out rule').toBe(true)
-  // The viewport-sized panel host must NOT inherit the shell's blanket
-  // `body > :not(#root) { no-drag }` — it would cancel every window-drag
-  // strip beneath it on macOS (issue #772). A text match only proves the
-  // declaration shipped, so this probe reproduces the SHELL's two darwin
-  // rules verbatim, flips the platform attribute the shell stamps, and reads
-  // the COMPUTED property: app-region is inherited and ignores
-  // pointer-events, so the loss shows on the host/layer — never on the strip
-  // itself (it computes `drag` in every configuration, which is why a fix
-  // validated only against the strip proves nothing).
+  // The plugin host is a direct body child, so on macOS it picks up the
+  // shell's blanket `body > :not(#root) { no-drag }` and — because app-region
+  // ignores pointer-events — the viewport-sized layer inside it cancelled every
+  // window-drag strip beneath it (issue #772). A text match only proves the
+  // declaration shipped, so this probe reproduces the SHELL's two darwin rules
+  // verbatim, flips the platform attribute the shell stamps, and reads the
+  // COMPUTED property. Two things to know when reading the expectations below:
+  // the strip itself computes `drag` in every configuration (a fix validated
+  // against the strip alone proves nothing), and `[data-dsh-panel-host]` is NOT
+  // a body child (it lives inside the host), so its own value is pinned by the
+  // unit guard rather than by this probe — see the `layer` expectation.
   const regions = await page.evaluate(() => {
     const style = document.createElement('style')
     style.textContent = [
@@ -660,8 +684,13 @@ test('conservative auto: URL stamps alone never modify the layout; plugin chrome
     return result
   })
   expect(regions.strip, 'the drag strip itself must keep computing `drag`').toBe('drag')
-  expect(regions.host, 'the plugin host must not inherit the shell no-drag').toBe('none')
-  expect(regions.layer, 'the panel host must not inherit the shell no-drag').toBe('none')
+  expect(regions.host, 'the plugin host must not take the shell blanket no-drag').toBe('none')
+  // NOT discriminating here, and kept as a regression nail only: the layer is
+  // not a body child, and this engine does not propagate the property into it,
+  // so it reads `none` pre- and post-fix. Its rule is pinned by
+  // tests/panel-host-css.spec.ts; in Electron (#772's CDP reading) the layer
+  // DOES end up no-drag through that propagation.
+  expect(regions.layer, 'the panel layer must keep its own reset').toBe('none')
   expect(regions.layerChild, 'panels stay no-drag so their controls keep receiving clicks').toBe('no-drag')
 })
 
diff --git a/tests/panel-host-css.spec.ts b/tests/panel-host-css.spec.ts
index f57f298..19da378 100644
--- a/tests/panel-host-css.spec.ts
+++ b/tests/panel-host-css.spec.ts
@@ -49,12 +49,14 @@ describe('panel host layer css', () => {
     // The shell's `html[data-platform=darwin] body > :not(#root) { no-drag }`
     // carries an id in its specificity, so only `initial !important` wins;
     // `initial` computes to the NEUTRAL `none` (does not subtract from the
-    // drag region) while `no-drag` is the subtracting value — hence the
-    // split: decorative viewport-sized layers opt out, their panels stay
-    // no-drag so controls keep receiving clicks. Dropping the `!important`
-    // silently re-breaks window drag / double-click-title zoom on macOS
-    // (there is no macOS runner to catch it), so pin the shape here where
-    // Linux `pnpm test` fails instead.
+    // drag region) while `no-drag` is the subtracting value — and the literal
+    // keyword `none` is NOT neutral (it computes to `no-drag`), which is
+    // exactly why this guard pins `initial`. Hence the split: decorative
+    // viewport-sized layers opt out, their panels stay no-drag so controls
+    // keep receiving clicks. Dropping the `!important` silently re-breaks
+    // window drag / double-click-title zoom on macOS (there is no macOS
+    // runner to catch it), so pin the shape here where Linux `pnpm test`
+    // fails instead.
     const text = stripComments(css)
     expect(text, 'the panel host must opt out of app-region computation').toMatch(
       /:global\(\[data-dsh-panel-host\]\)\s*\{[^}]*-webkit-app-region:\s*initial\s*!important/,
@@ -62,12 +64,21 @@ describe('panel host layer css', () => {
     expect(text, 'panels must stay no-drag').toMatch(
       /:global\(\[data-dsh-panel-host\]\)\s*>\s*\*\s*\{[^}]*-webkit-app-region:\s*no-drag/,
     )
-    expect(text, 'the mermaid zoom modal is the other viewport-sized body child').toMatch(
+    expect(text, 'the mermaid zoom modal is the other persistent viewport-sized body child').toMatch(
       /\.mermaidModal\s*\{[^}]*-webkit-app-region:\s*initial\s*!important/,
     )
     // The interactive popups must NOT get `initial`: they are buttons/handles
     // the shell already keeps no-drag, and outranking that rule makes a press
-    // start a window drag (the #103/#111 click-swallow class).
-    expect(text).not.toMatch(/\.selectionPopup\s*\{[^}]*-webkit-app-region:\s*initial/)
+    // start a window drag (the #103/#111 click-swallow class). Checked per
+    // DECLARATION BLOCK, not per single-selector rule: a selector list
+    // (`.selectionPopup, .other { … initial !important }`) would slip past a
+    // simple "class immediately followed by {" pattern.
+    const resets = [...text.matchAll(/([^{}]+)\{([^{}]*)\}/g)]
+      .filter(([, , body]) => /-webkit-app-region:\s*initial/.test(body ?? ''))
+    expect(resets.length, 'the file must declare the app-region opt-out').toBeGreaterThan(0)
+    const resetSelectors = resets.map(([, selector]) => selector ?? '').join(',')
+    for (const excluded of ['selectionPopup']) {
+      expect(resetSelectors, `${excluded} must not opt out of app-region`).not.toContain(excluded)
+    }
   })
 })