diff --git a/UI-DESIGN.md b/UI-DESIGN.md
index eae0a442..05a6fef8 100644
--- a/UI-DESIGN.md
+++ b/UI-DESIGN.md
@@ -333,9 +333,13 @@
 应用顶栏用于当前会话标题、范围、窗口级状态、侧栏开关和低频全局操作，不承担主要导航。
 顶栏必须保持紧凑，不能与页面内容争夺注意力。
 
-- 无边框窗口使用一条紧凑标题栏，保留侧栏开关、当前会话标题、范围、Runtime 状态、主题
-  开关和窗口控制，不得为了新增工作栏入口把这一整组控件下移。普通图标按钮使用
+- 应用壳层在水平方向分为全高主侧栏和右侧内容框架。主侧栏从窗口顶部贯穿到底部，品牌区、
+  项目切换器、导航和账户区保持同一连续表面；不能用全宽标题栏把整条侧栏向下推移。
+- 无边框窗口的紧凑标题栏只覆盖右侧内容框架，保留侧栏开关、当前会话标题、范围、Runtime
+  状态、主题开关和窗口控制，不得为了新增工作栏入口把这一整组控件下移。普通图标按钮使用
   `34px × 34px` 点击区域。
+- 发布说明 Modal 与其他应用级 Modal 一样使用整窗遮罩；遮罩必须覆盖主侧栏、右侧内容和
+  顶栏，不能保留一条未被遮罩的窗口控制色块。关闭操作由 Modal 自身提供。
 - 当前会话存在 Task 时，Task 上下文栏位于标题栏下方并承载任务摘要与详情；没有 Task 时
   整行隐藏。折叠状态保持为 `46px` 单行表面，与右侧工作栏标签栏等高，左右分隔线必须水平
   对齐。该栏不重复放置新建入口。
diff --git a/docs/prd/assistant-experience/assistant-workbar-and-execution-spaces-prd.md b/docs/prd/assistant-experience/assistant-workbar-and-execution-spaces-prd.md
index eaa7326c..1b83a617 100644
--- a/docs/prd/assistant-experience/assistant-workbar-and-execution-spaces-prd.md
+++ b/docs/prd/assistant-experience/assistant-workbar-and-execution-spaces-prd.md
@@ -221,6 +221,8 @@ Runtime
 - 分栏计算排除最左侧主导航，主工作区与工作栏使用相同的 `300px` 最小宽度。拖动记录两侧
   在可用分栏宽度中的比例；任一侧达到最小值后停止，窗口缩放后按原比例重新计算并再次
   应用同一最小值约束。
+- 最左侧主导航保持全高连续表面；窗口标题栏只覆盖右侧内容框架，不能横跨主导航并把品牌、
+  项目切换器和导航整体向下推移。
 - 对话内容与输入区始终保留对称的左右安全边距，工作栏边界不得覆盖或裁切输入框、发送
   按钮及主工作区右侧边距。
 - 唯一展开与收起开关固定在窗口关闭按钮正下方。工作栏内部不重复关闭入口。开关图标中的
diff --git a/src/renderer/src/App.test.tsx b/src/renderer/src/App.test.tsx
index ed75c8a7..5722258c 100644
--- a/src/renderer/src/App.test.tsx
+++ b/src/renderer/src/App.test.tsx
@@ -8028,8 +8028,17 @@ describe('App', () => {
     const assistantTrigger =
       screen.getByLabelText('切换助手工作栏')
     expect(assistantTrigger.parentElement).toBe(
+      container.querySelector('.app-content')
+    )
+    expect(container.querySelector('.sidebar')?.parentElement).toBe(
       container.querySelector('.app-shell')
     )
+    expect(container.querySelector('.app-frame')?.parentElement).toBe(
+      container.querySelector('.app-shell')
+    )
+    expect(container.querySelector('.topbar')?.parentElement).toBe(
+      container.querySelector('.app-frame')
+    )
     expect(assistantTrigger).toHaveClass('assistant-sidebar-toggle')
     expect(assistantTrigger).not.toHaveClass('icon-button--active')
     expect(assistantTrigger).toHaveAttribute('aria-expanded', 'false')
@@ -8582,7 +8591,7 @@ describe('App', () => {
         name: '助手工作栏'
       })
       expect(workbar).toHaveClass('assistant-sidebar--open')
-      expect(workbar.parentElement).toHaveClass('app-shell')
+      expect(workbar.parentElement).toHaveClass('app-content')
       expect(
         workbar.parentElement?.querySelector('main.workspace')
       ).toBeInTheDocument()
diff --git a/src/renderer/src/App.tsx b/src/renderer/src/App.tsx
index 16bd77aa..ab790e0d 100644
--- a/src/renderer/src/App.tsx
+++ b/src/renderer/src/App.tsx
@@ -7389,114 +7389,7 @@ function App(): React.JSX.Element {
   const backgroundIsolated = mainSidebarOpen
 
   return (
-    <div className="app-frame">
-      <header className="topbar">
-        <button
-          className="icon-button sidebar-toggle"
-          type="button"
-          aria-label={t('sidebar.toggle')}
-          onClick={() => setSidebarOpen((open) => !open)}
-          ref={sidebarToggleRef}
-        >
-          <PanelLeft aria-hidden="true" size={18} />
-        </button>
-        {view === 'chat' && (
-          <>
-            <div
-              className="conversation-title"
-              title={activeConversation?.title}
-            >
-              <span className="conversation-title__text">
-                {activeConversation
-                  ? getConversationDisplayTitle(
-                      activeConversation,
-                      t('conversation.defaultTitle')
-                    )
-                  :
-                  (activeProject?.kind === 'channel'
-                    ? t('conversation.remoteTitle')
-                    : t('conversation.defaultTitle'))}
-              </span>
-              {activeConversation?.branch && (
-                <ConversationBranchBadge
-                  sourceTitle={
-                    conversationTitles.get(
-                      activeConversation.branch.sourceConversationId
-                    ) ?? activeConversation.branch.sourceTitle
-                  }
-                />
-              )}
-              {activeConversation?.remote && (
-                <b className="conversation-source-badge">
-                  {
-                    projectChannelLabels[
-                      activeConversation.remote.channel
-                    ]
-                  }
-                </b>
-              )}
-            </div>
-            <ScopeBadge
-              scope={
-                activeProject
-                  ? {
-                      kind: 'project',
-                      projectName:
-                        activeProjectDisplayName ?? activeProject.name
-                    }
-                  : {
-                      kind: 'unavailable',
-                      explanation: t('notices.projectNotLoaded')
-                    }
-              }
-            />
-          </>
-        )}
-        <div className="topbar__actions">
-          <span
-            className={
-              runtime?.available
-                ? 'runtime-status runtime-status--online'
-                : 'runtime-status'
-            }
-            title={runtime?.detail}
-          >
-            <span className="runtime-status__dot" />
-            <span className="runtime-status__label">
-              {runtime?.label ?? t('runtime.detecting')}
-            </span>
-            {runtime?.capability === 'image-generation' && (
-              <span className="runtime-capability-badge">
-                {t('runtime.imageGeneration')}
-              </span>
-            )}
-          </span>
-          <button
-            aria-label={
-              resolvedAppearanceTheme === 'dark'
-                ? t('topbar.switchLight')
-                : t('topbar.switchDark')
-            }
-            aria-pressed={resolvedAppearanceTheme === 'dark'}
-            className="icon-button theme-toggle-button"
-            onClick={toggleAppearanceTheme}
-            title={
-              resolvedAppearanceTheme === 'dark'
-                ? t('topbar.switchLight')
-                : t('topbar.switchDark')
-            }
-            type="button"
-          >
-            {resolvedAppearanceTheme === 'dark' ? (
-              <Sun aria-hidden="true" size={18} />
-            ) : (
-              <Moon aria-hidden="true" size={18} />
-            )}
-          </button>
-        </div>
-        <WindowControls onError={handleWindowControlError} />
-      </header>
-      <div className="app-shell">
+    <div className="app-shell">
       <aside
         aria-label={
           narrowWindow && sidebarOpen ? t('sidebar.label') : undefined
@@ -8148,32 +8041,141 @@ function App(): React.JSX.Element {
         />
       )}
 
-      {view === 'chat' && (
-        <button
-          aria-controls="assistant-sidebar"
-          aria-expanded={assistantSidebarOpen}
-          aria-label={t('topbar.toggleAssistantSidebar')}
-          className="icon-button assistant-sidebar-toggle"
-          onClick={() =>
-            setAssistantSidebarOpen((current) => !current)
-          }
-          ref={assistantSidebarToggleRef}
-          title={t('topbar.toggleAssistantSidebar')}
-          type="button"
-        >
-          {assistantSidebarOpen ? (
-            <PanelRightClose aria-hidden="true" size={18} />
-          ) : (
-            <PanelRightOpen aria-hidden="true" size={18} />
+      <div className="app-frame">
+        <header className="topbar">
+          <button
+            className="icon-button sidebar-toggle"
+            type="button"
+            aria-label={t('sidebar.toggle')}
+            onClick={() => setSidebarOpen((open) => !open)}
+            ref={sidebarToggleRef}
+          >
+            <PanelLeft aria-hidden="true" size={18} />
+          </button>
+          {view === 'chat' && (
+            <>
+              <div
+                className="conversation-title"
+                title={activeConversation?.title}
+              >
+                <span className="conversation-title__text">
+                  {activeConversation
+                    ? getConversationDisplayTitle(
+                        activeConversation,
+                        t('conversation.defaultTitle')
+                      )
+                    :
+                    (activeProject?.kind === 'channel'
+                      ? t('conversation.remoteTitle')
+                      : t('conversation.defaultTitle'))}
+                </span>
+                {activeConversation?.branch && (
+                  <ConversationBranchBadge
+                    sourceTitle={
+                      conversationTitles.get(
+                        activeConversation.branch.sourceConversationId
+                      ) ?? activeConversation.branch.sourceTitle
+                    }
+                  />
+                )}
+                {activeConversation?.remote && (
+                  <b className="conversation-source-badge">
+                    {
+                      projectChannelLabels[
+                        activeConversation.remote.channel
+                      ]
+                    }
+                  </b>
+                )}
+              </div>
+              <ScopeBadge
+                scope={
+                  activeProject
+                    ? {
+                        kind: 'project',
+                        projectName:
+                          activeProjectDisplayName ?? activeProject.name
+                      }
+                    : {
+                        kind: 'unavailable',
+                        explanation: t('notices.projectNotLoaded')
+                      }
+                }
+              />
+            </>
           )}
-        </button>
-      )}
+          <div className="topbar__actions">
+            <span
+              className={
+                runtime?.available
+                  ? 'runtime-status runtime-status--online'
+                  : 'runtime-status'
+              }
+              title={runtime?.detail}
+            >
+              <span className="runtime-status__dot" />
+              <span className="runtime-status__label">
+                {runtime?.label ?? t('runtime.detecting')}
+              </span>
+              {runtime?.capability === 'image-generation' && (
+                <span className="runtime-capability-badge">
+                  {t('runtime.imageGeneration')}
+                </span>
+              )}
+            </span>
+            <button
+              aria-label={
+                resolvedAppearanceTheme === 'dark'
+                  ? t('topbar.switchLight')
+                  : t('topbar.switchDark')
+              }
+              aria-pressed={resolvedAppearanceTheme === 'dark'}
+              className="icon-button theme-toggle-button"
+              onClick={toggleAppearanceTheme}
+              title={
+                resolvedAppearanceTheme === 'dark'
+                  ? t('topbar.switchLight')
+                  : t('topbar.switchDark')
+              }
+              type="button"
+            >
+              {resolvedAppearanceTheme === 'dark' ? (
+                <Sun aria-hidden="true" size={18} />
+              ) : (
+                <Moon aria-hidden="true" size={18} />
+              )}
+            </button>
+          </div>
+          <WindowControls onError={handleWindowControlError} />
+        </header>
 
-      <main
-        aria-hidden={backgroundIsolated ? 'true' : undefined}
-        className="workspace"
-        inert={backgroundIsolated}
-      >
+        <div className="app-content">
+          {view === 'chat' && (
+            <button
+              aria-controls="assistant-sidebar"
+              aria-expanded={assistantSidebarOpen}
+              aria-label={t('topbar.toggleAssistantSidebar')}
+              className="icon-button assistant-sidebar-toggle"
+              onClick={() =>
+                setAssistantSidebarOpen((current) => !current)
+              }
+              ref={assistantSidebarToggleRef}
+              title={t('topbar.toggleAssistantSidebar')}
+              type="button"
+            >
+              {assistantSidebarOpen ? (
+                <PanelRightClose aria-hidden="true" size={18} />
+              ) : (
+                <PanelRightOpen aria-hidden="true" size={18} />
+              )}
+            </button>
+          )}
+
+          <main
+            aria-hidden={backgroundIsolated ? 'true' : undefined}
+            className="workspace"
+            inert={backgroundIsolated}
+          >
         {(view === 'chat' || cachedWorkspaceViewKeys.has('chat')) && (
           <KeepAliveRoute
             active={view === 'chat'}
@@ -9882,7 +9884,8 @@ function App(): React.JSX.Element {
         tab={assistantSidebarTab}
         workspaceChanges={workspaceChanges}
         workspaceProjectId={activeProjectId || undefined}
-      />
+          />
+        </div>
       </div>
     </div>
   )
diff --git a/src/renderer/src/WorkspacePrimitives.test.tsx b/src/renderer/src/WorkspacePrimitives.test.tsx
index bb1659fe..f8577c8a 100644
--- a/src/renderer/src/WorkspacePrimitives.test.tsx
+++ b/src/renderer/src/WorkspacePrimitives.test.tsx
@@ -199,7 +199,16 @@ describe('WorkspacePrimitives', () => {
       /\.assistant-sidebar__tab\s*\{[^}]*white-space:\s*nowrap;/u
     )
     expect(stylesheet).toMatch(
-      /\.app-frame\s*\{[^}]*display:\s*grid;[^}]*grid-template-rows:\s*58px minmax\(0,\s*1fr\);/u
+      /\.app-frame\s*\{[^}]*display:\s*grid;[^}]*flex:\s*1;[^}]*grid-template-rows:\s*58px minmax\(0,\s*1fr\);/u
+    )
+    expect(stylesheet).toMatch(
+      /\.app-shell\s*\{[^}]*display:\s*flex;[^}]*width:\s*100%;[^}]*height:\s*100%;/u
+    )
+    expect(stylesheet).toMatch(
+      /\.release-notes-backdrop\s*\{[^}]*position:\s*fixed;[^}]*background:\s*var\(--overlay-backdrop\);[^}]*inset:\s*0;/u
+    )
+    expect(stylesheet).toMatch(
+      /\.app-content\s*\{[^}]*position:\s*relative;[^}]*display:\s*flex;[^}]*width:\s*100%;[^}]*height:\s*100%;/u
     )
     expect(stylesheet).toMatch(
       /\.workspace\s*\{[^}]*grid-template-rows:\s*minmax\(0,\s*1fr\);/u
diff --git a/src/renderer/src/styles.css b/src/renderer/src/styles.css
index ad272160..1f0fdf48 100644
--- a/src/renderer/src/styles.css
+++ b/src/renderer/src/styles.css
@@ -2270,8 +2270,8 @@ textarea:focus-visible {
 .app-frame {
   position: relative;
   display: grid;
-  width: 100%;
   height: 100%;
+  flex: 1;
   min-width: 0;
   min-height: 0;
   background: var(--surface-canvas);
@@ -2290,6 +2290,17 @@ textarea:focus-visible {
   color: var(--text-primary);
 }
 
+.app-content {
+  position: relative;
+  display: flex;
+  width: 100%;
+  height: 100%;
+  min-width: 0;
+  min-height: 0;
+  background: var(--surface-canvas);
+  color: var(--text-primary);
+}
+
 .sidebar {
   display: flex;
   flex: 0 0 278px;
@@ -5411,7 +5422,7 @@ button > svg {
   display: grid;
   padding: var(--space-4);
   background: var(--overlay-backdrop);
-  inset: 38px 0 0;
+  inset: 0;
   place-items: center;
 }
 
@@ -12558,7 +12569,7 @@ details.settings-section > :not(summary) + :not(summary) {
   --shadow-dialog: 0 18px 48px rgb(0 4 10 / 48%);
 }
 
-:root[data-theme='dark'] :where(.app-frame, .app-shell) {
+:root[data-theme='dark'] :where(.app-frame, .app-shell, .app-content) {
   background: var(--surface-canvas);
   color: var(--text-primary);
 }