diff --git a/desktop/src/components/controls/ReasoningEffortPopover.test.tsx b/desktop/src/components/controls/ReasoningEffortPopover.test.tsx
index 09ef39c8..10cf4d13 100644
--- a/desktop/src/components/controls/ReasoningEffortPopover.test.tsx
+++ b/desktop/src/components/controls/ReasoningEffortPopover.test.tsx
@@ -44,16 +44,16 @@ describe('ReasoningEffortPopover', () => {
     renderPopover()
 
     const popover = screen.getByTestId('reasoning-effort-popover')
-    expect(popover).toHaveStyle({ width: '280px' })
-    expect(popover).toHaveClass('px-4', 'pb-4', 'pt-3.5')
+    expect(popover).toHaveStyle({ width: '240px' })
+    expect(popover).toHaveClass('px-3.5', 'pb-3.5', 'pt-3')
     expect(popover.querySelectorAll('svg')).toHaveLength(0)
-    expect(screen.getByTestId('reasoning-effort-header')).toHaveClass('mb-3', 'justify-between')
-    expect(screen.getByTestId('reasoning-effort-label')).toHaveClass('text-[15px]')
-    expect(screen.getByTestId('reasoning-effort-context-label')).toHaveClass('text-[11px]')
+    expect(screen.getByTestId('reasoning-effort-header')).toHaveClass('mb-2.5', 'justify-between')
+    expect(screen.getByTestId('reasoning-effort-label')).toHaveClass('text-sm')
+    expect(screen.getByTestId('reasoning-effort-context-label')).toHaveClass('text-[10px]')
     expect(screen.getByTestId('reasoning-effort-context-label')).toHaveTextContent('推理强度')
-    expect(screen.getByRole('slider', { name: '推理强度' })).toHaveClass('h-11')
-    expect(screen.getByTestId('reasoning-effort-track')).toHaveClass('h-[30px]')
-    expect(screen.getByTestId('reasoning-effort-thumb')).toHaveClass('h-10', 'w-10')
+    expect(screen.getByRole('slider', { name: '推理强度' })).toHaveClass('h-9')
+    expect(screen.getByTestId('reasoning-effort-track')).toHaveClass('h-6')
+    expect(screen.getByTestId('reasoning-effort-thumb')).toHaveClass('h-8', 'w-8')
   })
 
   it('renders every model-supported stop and exposes the selected localized value', () => {
diff --git a/desktop/src/components/controls/ReasoningEffortPopover.tsx b/desktop/src/components/controls/ReasoningEffortPopover.tsx
index cfaf3cd9..c87666d0 100644
--- a/desktop/src/components/controls/ReasoningEffortPopover.tsx
+++ b/desktop/src/components/controls/ReasoningEffortPopover.tsx
@@ -20,7 +20,7 @@ type PopoverPosition = {
   width: number
 }
 
-const POPOVER_WIDTH = 280
+const POPOVER_WIDTH = 240
 const VIEWPORT_MARGIN = 16
 const POPOVER_GAP = 10
 
@@ -107,22 +107,22 @@ export function ReasoningEffortPopover({
     <div
       ref={popoverRef}
       data-testid="reasoning-effort-popover"
-      className="fixed z-[90] rounded-[18px] border border-[var(--color-border)] bg-[var(--color-surface-container-lowest)] px-4 pb-4 pt-3.5 shadow-[0_14px_36px_rgba(15,23,42,0.14)]"
+      className="fixed z-[90] rounded-2xl border border-[var(--color-border)] bg-[var(--color-surface-container-lowest)] px-3.5 pb-3.5 pt-3 shadow-[0_12px_30px_rgba(15,23,42,0.13)]"
       style={{ bottom: position.bottom, left: position.left, width: position.width }}
     >
       <div
         data-testid="reasoning-effort-header"
-        className="mb-3 flex items-baseline justify-between gap-3"
+        className="mb-2.5 flex items-baseline justify-between gap-3"
       >
         <div
           data-testid="reasoning-effort-label"
-          className="text-[15px] font-semibold text-[var(--color-text-secondary)]"
+          className="text-sm font-semibold text-[var(--color-text-secondary)]"
         >
           {labels[value]}
         </div>
         <div
           data-testid="reasoning-effort-context-label"
-          className="text-[11px] font-medium tracking-wide text-[var(--color-text-tertiary)]"
+          className="text-[10px] font-medium tracking-wide text-[var(--color-text-tertiary)]"
         >
           {ariaLabel}
         </div>
@@ -137,7 +137,7 @@ export function ReasoningEffortPopover({
         aria-valuemax={maxIndex}
         aria-valuenow={selectedIndex}
         aria-valuetext={labels[value]}
-        className="group relative flex h-11 touch-none cursor-pointer items-center outline-none focus-visible:ring-2 focus-visible:ring-[var(--color-brand)] focus-visible:ring-offset-4 focus-visible:ring-offset-[var(--color-surface-container-lowest)]"
+        className="group relative flex h-9 touch-none cursor-pointer items-center outline-none focus-visible:ring-2 focus-visible:ring-[var(--color-brand)] focus-visible:ring-offset-3 focus-visible:ring-offset-[var(--color-surface-container-lowest)]"
         onClick={(event) => selectFromClientX(event.clientX)}
         onPointerDown={(event) => {
           draggingRef.current = true
@@ -182,7 +182,7 @@ export function ReasoningEffortPopover({
       >
         <div
           data-testid="reasoning-effort-track"
-          className="absolute inset-x-0 h-[30px] overflow-hidden rounded-full bg-[var(--color-surface-container-high)] shadow-[inset_0_0_0_1px_var(--color-border)]"
+          className="absolute inset-x-0 h-6 overflow-hidden rounded-full bg-[var(--color-surface-container-high)] shadow-[inset_0_0_0_1px_var(--color-border)]"
         >
           <div
             data-testid="reasoning-effort-fill"
@@ -191,12 +191,12 @@ export function ReasoningEffortPopover({
           />
         </div>
 
-        <div className="absolute inset-x-0 flex items-center justify-between px-[22px]">
+        <div className="absolute inset-x-0 flex items-center justify-between px-[18px]">
           {options.map((option, index) => (
             <span
               key={option}
               data-testid="reasoning-effort-stop"
-              className={`h-2 w-2 rounded-full ${index <= selectedIndex ? 'bg-white/45' : 'bg-[var(--color-outline)]/55'}`}
+              className={`h-1.5 w-1.5 rounded-full ${index <= selectedIndex ? 'bg-white/45' : 'bg-[var(--color-outline)]/55'}`}
             />
           ))}
         </div>
@@ -204,7 +204,7 @@ export function ReasoningEffortPopover({
         <div
           aria-hidden="true"
           data-testid="reasoning-effort-thumb"
-          className="absolute top-1/2 h-10 w-10 -translate-x-1/2 -translate-y-1/2 rounded-full border border-[var(--color-border)] bg-white shadow-[0_3px_9px_rgba(15,23,42,0.14)] transition-[left] duration-200 motion-reduce:transition-none"
+          className="absolute top-1/2 h-8 w-8 -translate-x-1/2 -translate-y-1/2 rounded-full border border-[var(--color-border)] bg-white shadow-[0_2px_7px_rgba(15,23,42,0.13)] transition-[left] duration-200 motion-reduce:transition-none"
           style={{ left: `${fillPercent}%` }}
         />
       </div>
diff --git a/desktop/src/components/layout/TabBar.test.tsx b/desktop/src/components/layout/TabBar.test.tsx
index 99c3fde2..ba4e6078 100644
--- a/desktop/src/components/layout/TabBar.test.tsx
+++ b/desktop/src/components/layout/TabBar.test.tsx
@@ -295,11 +295,12 @@ describe('TabBar', () => {
     expect(screen.queryByTestId('session-activity-badge')).not.toBeInTheDocument()
   })
 
-  it('shows the activity button for completed TodoWrite history without a badge', async () => {
+  it('shows the activity button for completed TodoWrite history and hides it while the workspace is open', async () => {
     const { TabBar } = await import('./TabBar')
     const { useTabStore } = await import('../../stores/tabStore')
     const { useChatStore } = await import('../../stores/chatStore')
     const { useSessionStore } = await import('../../stores/sessionStore')
+    const { useWorkspacePanelStore } = await import('../../stores/workspacePanelStore')
     const sessionId = 'session-1'
     const chatSession = makeChatSession('idle')
     chatSession.messages = [completedTodoWriteMessage()]
@@ -324,6 +325,12 @@ describe('TabBar', () => {
 
     expect(screen.getByRole('button', { name: /activity/i })).toBeInTheDocument()
     expect(screen.queryByTestId('session-activity-badge')).not.toBeInTheDocument()
+
+    act(() => {
+      useWorkspacePanelStore.getState().openPanel(sessionId)
+    })
+
+    expect(screen.queryByRole('button', { name: /activity/i })).not.toBeInTheDocument()
   })
 
   it('shows the activity button without a numeric badge for running or failed activity', async () => {
diff --git a/desktop/src/components/layout/TabBar.tsx b/desktop/src/components/layout/TabBar.tsx
index 83c10d6d..4d3644c3 100644
--- a/desktop/src/components/layout/TabBar.tsx
+++ b/desktop/src/components/layout/TabBar.tsx
@@ -141,7 +141,7 @@ export function TabBar() {
       hasVisibleActivity: hasVisibleSessionActivity(model),
     }
   }))
-  const showActivityButton = activeTabId && activityState.hasVisibleActivity
+  const showActivityButton = activeTabId && activityState.hasVisibleActivity && !isWorkbenchOpen
 
   const moveTab = useTabStore((s) => s.moveTab)
   const scrollRef = useRef<HTMLDivElement>(null)
diff --git a/desktop/src/pages/ActiveSession.test.tsx b/desktop/src/pages/ActiveSession.test.tsx
index 9b2fb794..e01c8a9b 100644
--- a/desktop/src/pages/ActiveSession.test.tsx
+++ b/desktop/src/pages/ActiveSession.test.tsx
@@ -468,7 +468,7 @@ describe('ActiveSession task polling', () => {
     expect(screen.queryByTestId('background-tasks-button')).not.toBeInTheDocument()
   })
 
-  it('renders the activity panel inside the chat column with session activity rows', () => {
+  it('renders the activity panel as a rail and hides it when the workspace opens', async () => {
     const sessionId = 'activity-panel-open-session'
 
     useCLITaskStore.setState({
@@ -577,6 +577,16 @@ describe('ActiveSession task polling', () => {
     expect(chatColumn).toContainElement(screen.getByTestId('chat-input'))
     expect(screen.queryByTestId('session-task-bar')).not.toBeInTheDocument()
     expect(screen.queryByTestId('background-tasks-button')).not.toBeInTheDocument()
+
+    act(() => {
+      useWorkspacePanelStore.getState().openPanel(sessionId)
+    })
+
+    expect(screen.getByTestId('workbench-panel')).toBeInTheDocument()
+    expect(screen.queryByTestId('session-activity-panel')).not.toBeInTheDocument()
+    await waitFor(() => {
+      expect(useActivityPanelStore.getState().isOpen(sessionId)).toBe(false)
+    })
   })
 
   it('does not render the activity panel when the store is open without visible activity', async () => {
diff --git a/desktop/src/pages/ActiveSession.tsx b/desktop/src/pages/ActiveSession.tsx
index 4262e259..d73f9d79 100644
--- a/desktop/src/pages/ActiveSession.tsx
+++ b/desktop/src/pages/ActiveSession.tsx
@@ -477,6 +477,11 @@ export function ActiveSession() {
     closeActivityPanel(activeTabId)
   }, [activeTabId, closeActivityPanel, hasVisibleActivity, isActivityPanelOpen])
 
+  useEffect(() => {
+    if (!activeTabId || !showWorkbench || !isActivityPanelOpen) return
+    closeActivityPanel(activeTabId)
+  }, [activeTabId, closeActivityPanel, isActivityPanelOpen, showWorkbench])
+
   const handleOpenSubagentRun = useCallback((payload: { sessionId: string; toolUseId: string; title: string }) => {
     useTabStore.getState().openSubagentTab(payload.sessionId, payload.toolUseId, payload.title)
   }, [])
@@ -725,7 +730,7 @@ export function ActiveSession() {
           ) : null}
         </div>
 
-        {activityModel && hasVisibleActivity && !isMobileLayout && !isMemberSession && isSessionTabState(activeTabId, activeTabType) ? (
+        {activityModel && hasVisibleActivity && !showWorkbench && !isMobileLayout && !isMemberSession && isSessionTabState(activeTabId, activeTabType) ? (
           <SessionActivityPanel
             model={activityModel}
             open={isActivityPanelOpen}