diff --git a/apps/web/tests/markdown-images.e2e.ts b/apps/web/tests/markdown-images.e2e.ts
index 122abebc73..390675a3d1 100644
--- a/apps/web/tests/markdown-images.e2e.ts
+++ b/apps/web/tests/markdown-images.e2e.ts
@@ -289,7 +289,18 @@ describe('web e2e: Markdown image rendering', () => {
     await page.getByRole('button', { name: `View full image: ${WORKSPACE_ALT}`, exact: true }).click()
     const lightbox = page.getByRole('dialog', { name: 'Image preview', exact: true })
     await lightbox.waitFor()
-    await lightbox.getByRole('button', { name: 'Close image preview' }).click()
+    const lightboxMask = lightbox.locator(':scope > div > [aria-hidden="true"]')
+    const lightboxClose = lightbox.getByRole('button', { name: 'Close image preview' })
+    for (const windows of [true, false]) {
+      await page.evaluate((value) => {
+        document.documentElement.toggleAttribute('data-windows-titlebar', value)
+        document.documentElement.style.setProperty('--dsh-windows-titlebar-height', value ? '40px' : '')
+      }, windows)
+      // The Windows caption stays unpainted and the close control sits below it.
+      expect((await lightboxMask.boundingBox())?.y).toBe(windows ? 40 : 0)
+      expect((await lightboxClose.boundingBox())?.y).toBe(windows ? 60 : 20)
+    }
+    await lightboxClose.click()
     await lightbox.waitFor({ state: 'detached' })
     const link = page.getByRole('button', { name: 'View comparison', exact: true })
     await link.hover()
diff --git a/packages/client/ui-primitives/README.i18n.yaml b/packages/client/ui-primitives/README.i18n.yaml
index fa11b9567d..06cd120754 100644
--- a/packages/client/ui-primitives/README.i18n.yaml
+++ b/packages/client/ui-primitives/README.i18n.yaml
@@ -24,8 +24,8 @@
   en: f0e54915b896af5a
   zh: 2047520fd321be90
 /deepseek-ai-dsh-client-ui-primitives/use-this-package/rendering-agent-output:
-  en: d79e20306593c4bf
-  zh: 5c0f1100e2cd6fcc
+  en: 4a1a61bb2d64fe4c
+  zh: 1b0097fff440c2ef
 /deepseek-ai-dsh-client-ui-primitives/use-this-package/localizing-copy:
   en: 4aef65dea11de083
   zh: abc22cd7c65cdf38
diff --git a/packages/client/ui-primitives/README.md b/packages/client/ui-primitives/README.md
index d627534fdd..509fdd62fe 100644
--- a/packages/client/ui-primitives/README.md
+++ b/packages/client/ui-primitives/README.md
@@ -106,7 +106,7 @@ The nearest `MarkdownDelegateProvider` supplies optional `openExternalLink` and
 
 `JsonTree` clamps collapsed strings to `collapsedStringLines` (three by default). Expanded strings show raw text, retain sibling commas, and fit within the window and outer scrolling containers. Resize and ancestor-scroll events update that limit. Row copy feedback updates independently of JSON value rendering; pending clipboard writes cannot update a different row or an unmounted tree.
 
-`ImageLightbox` is the shared original-image modal with focus restoration and Escape dismissal. The internal thumbnail renderer receives loading/failure labels from its owner. `HoverCard.inline` keeps a file link in the text flow and uses the shared menu material, keyboard-visible focus, and placement above or below the anchor without covering it. Escape closes an open thumbnail even when focus is elsewhere; subsequent Escape presses reach the owner. `MarkdownDelegateProvider.fileImages` supplies a decoded-path resolver and complete image labels: settled image links gain hover previews, and standalone images gain lightbox activation. Image-only anchors retain their single navigation target. The parser recovers only complete, unescaped, standalone local image references with bare spaces and an unambiguous supported image suffix; code and ambiguous destinations remain literal.
+`ImageLightbox` is the shared original-image modal with focus restoration and Escape dismissal. Like `Modal`, its mask leaves the Windows caption unpainted, and its close control sits 20px below the caption. The internal thumbnail renderer receives loading/failure labels from its owner. `HoverCard.inline` keeps a file link in the text flow and uses the shared menu material, keyboard-visible focus, and placement above or below the anchor without covering it. Escape closes an open thumbnail even when focus is elsewhere; subsequent Escape presses reach the owner. `MarkdownDelegateProvider.fileImages` supplies a decoded-path resolver and complete image labels: settled image links gain hover previews, and standalone images gain lightbox activation. Image-only anchors retain their single navigation target. The parser recovers only complete, unescaped, standalone local image references with bare spaces and an unambiguous supported image suffix; code and ambiguous destinations remain literal.
 
 ### Localizing copy
 
diff --git a/packages/client/ui-primitives/README.zh.md b/packages/client/ui-primitives/README.zh.md
index 82d0419260..1f458060ed 100644
--- a/packages/client/ui-primitives/README.zh.md
+++ b/packages/client/ui-primitives/README.zh.md
@@ -106,7 +106,7 @@ kind: "package-library"
 
 `JsonTree` 把折叠字符串限制为 `collapsedStringLines` 行（默认三行）。展开后显示原始文本、保留同级逗号，并限制在窗口与外层滚动容器内；尺寸变化和祖先滚动事件会更新此限制。行复制反馈独立于 JSON 值渲染更新；尚未完成的剪贴板写入不会更新另一行或已卸载的树。
 
-`ImageLightbox` 是共享原图浮层，支持焦点恢复与 Esc 关闭。包内缩略图渲染器由调用方提供加载及失败文案。`HoverCard.inline` 使文件链接保持在文本流内，并使用共享菜单材质、键盘可见焦点，并在锚点上方或下方定位而不遮挡锚点。即使焦点位于其他位置，Esc 也会关闭已打开的缩略图；后续 Esc 按键继续传给 owner。`MarkdownDelegateProvider.fileImages` 提供已解码路径解析器与完整图片文案：消息落定后的图片链接支持悬停预览，独立图片支持点击放大。仅包含图片的链接保留单一导航目标。解析器仅恢复完整、未转义、独立成段且带明确图片扩展名的含裸空格本地图片引用；代码与有歧义的目标保持原文。
+`ImageLightbox` 是共享原图浮层，支持焦点恢复与 Esc 关闭。与 `Modal` 相同，其遮罩不覆盖 Windows 顶栏，关闭按钮位于顶栏下方 20px。包内缩略图渲染器由调用方提供加载及失败文案。`HoverCard.inline` 使文件链接保持在文本流内，并使用共享菜单材质、键盘可见焦点，并在锚点上方或下方定位而不遮挡锚点。即使焦点位于其他位置，Esc 也会关闭已打开的缩略图；后续 Esc 按键继续传给 owner。`MarkdownDelegateProvider.fileImages` 提供已解码路径解析器与完整图片文案：消息落定后的图片链接支持悬停预览，独立图片支持点击放大。仅包含图片的链接保留单一导航目标。解析器仅恢复完整、未转义、独立成段且带明确图片扩展名的含裸空格本地图片引用；代码与有歧义的目标保持原文。
 
 ### 本地化文案
 
diff --git a/packages/client/ui-primitives/src/ImageLightbox.module.css b/packages/client/ui-primitives/src/ImageLightbox.module.css
index 1907fe930f..4cffa16c36 100644
--- a/packages/client/ui-primitives/src/ImageLightbox.module.css
+++ b/packages/client/ui-primitives/src/ImageLightbox.module.css
@@ -1,9 +1,17 @@
+/* Full-viewport layer that blocks background clicks, including on the Windows caption. */
 .backdrop {
   position: fixed;
   inset: 0;
   z-index: 1000;
-  display: grid;
-  place-items: center;
+}
+
+/* Painted area below the Windows caption; like Modal, the caption stays unpainted. */
+.stage {
+  position: absolute;
+  inset: var(--dsh-frame-chrome-top, 0px) 0 0;
+  display: flex;
+  align-items: center;
+  justify-content: center;
   padding: 40px;
 }
 
@@ -18,7 +26,7 @@
 .image {
   position: relative;
   max-width: min(100%, 1600px);
-  max-height: calc(100vh - 80px);
+  max-height: 100%;
   object-fit: contain;
   border-radius: var(--dsw-radius-lg);
   background: var(--dsw-specific-input-major);
@@ -27,7 +35,7 @@
 }
 
 .close {
-  position: fixed;
+  position: absolute;
   top: 20px;
   right: 20px;
   z-index: 1;
diff --git a/packages/client/ui-primitives/src/ImageLightbox.tsx b/packages/client/ui-primitives/src/ImageLightbox.tsx
index 893ed2fe95..1cb3fe4a8c 100644
--- a/packages/client/ui-primitives/src/ImageLightbox.tsx
+++ b/packages/client/ui-primitives/src/ImageLightbox.tsx
@@ -54,11 +54,13 @@ export function ImageLightbox({ src, alt, labels, onClose }: {
       aria-modal="true"
       aria-label={labels.dialog}
     >
-      <div className={css.mask} aria-hidden="true" onMouseDown={onClose} />
-      <img className={css.image} src={src} alt={alt} />
-      <button ref={closeRef} type="button" className={css.close} aria-label={labels.close} onClick={onClose}>
-        <IconCloseOutlineRegular size={16} />
-      </button>
+      <div className={css.stage}>
+        <div className={css.mask} aria-hidden="true" onMouseDown={onClose} />
+        <img className={css.image} src={src} alt={alt} />
+        <button ref={closeRef} type="button" className={css.close} aria-label={labels.close} onClick={onClose}>
+          <IconCloseOutlineRegular size={16} />
+        </button>
+      </div>
     </div>,
     document.body,
   )