diff --git a/desktop/src/components/chat/ConversationNavigator.test.tsx b/desktop/src/components/chat/ConversationNavigator.test.tsx
index 56534d5d..2cf1cb9a 100644
--- a/desktop/src/components/chat/ConversationNavigator.test.tsx
+++ b/desktop/src/components/chat/ConversationNavigator.test.tsx
@@ -84,6 +84,7 @@ describe('ConversationNavigator', () => {
   it('renders ordered role markers and identifies the active target', () => {
     render(
       <ConversationNavigator
+        mode="full"
         items={[
           { id: 'user-1', renderItemKey: 'user-1', renderIndex: 0, role: 'user', preview: 'First prompt', attachmentCount: 0 },
           { id: 'assistant-1', renderItemKey: 'assistant-1', renderIndex: 1, role: 'assistant', preview: 'First answer', attachmentCount: 0 },
@@ -97,6 +98,55 @@ describe('ConversationNavigator', () => {
     expect(markers.map((marker) => marker.getAttribute('data-role'))).toEqual(['user', 'assistant'])
     expect(markers[0]?.getAttribute('aria-current')).toBeNull()
     expect(markers[1]?.getAttribute('aria-current')).toBe('location')
+
+    const markerBars = markers.map((marker) => marker.querySelector('[aria-hidden="true"]'))
+    expect(screen.getByTestId('conversation-navigator').getAttribute('data-mode')).toBe('full')
+    expect(markerBars.every((bar) => bar?.className.includes('w-3'))).toBe(true)
+    expect(markerBars.every((bar) => bar?.className.includes('group-hover:w-5'))).toBe(true)
+    expect(markerBars.every((bar) => bar?.className.includes('group-focus-visible:w-5'))).toBe(true)
+    expect(markerBars[1]?.className).toContain('bg-[var(--color-brand)]')
+    expect(markerBars[1]?.className.split(/\s+/)).not.toContain('w-5')
+  })
+
+  it('uses equal shorter marker geometry in compact mode', () => {
+    render(
+      <ConversationNavigator
+        mode="compact"
+        items={[
+          { id: 'user-1', renderItemKey: 'user-1', renderIndex: 0, role: 'user', preview: 'First prompt', attachmentCount: 0 },
+          { id: 'assistant-1', renderItemKey: 'assistant-1', renderIndex: 1, role: 'assistant', preview: 'First answer', attachmentCount: 0 },
+        ]}
+        activeItemId="user-1"
+        onNavigate={vi.fn()}
+      />,
+    )
+
+    const markers = screen.getAllByRole('button')
+    const markerBars = markers.map((marker) => marker.querySelector('[aria-hidden="true"]'))
+    expect(screen.getByTestId('conversation-navigator').getAttribute('data-mode')).toBe('compact')
+    expect(markerBars.every((bar) => bar?.className.includes('w-2.5'))).toBe(true)
+    expect(markerBars.every((bar) => bar?.className.includes('group-hover:w-4'))).toBe(true)
+    expect(markerBars.every((bar) => bar?.className.includes('motion-reduce:transition-none'))).toBe(true)
+  })
+
+  it('uses an edge-sized lane when the transcript becomes narrow', () => {
+    render(
+      <ConversationNavigator
+        mode="edge"
+        items={[
+          { id: 'user-1', renderItemKey: 'user-1', renderIndex: 0, role: 'user', preview: 'First prompt', attachmentCount: 0 },
+          { id: 'assistant-1', renderItemKey: 'assistant-1', renderIndex: 1, role: 'assistant', preview: 'First answer', attachmentCount: 0 },
+        ]}
+        activeItemId="assistant-1"
+        onNavigate={vi.fn()}
+      />,
+    )
+
+    const markers = screen.getAllByRole('button')
+    const markerBars = markers.map((marker) => marker.querySelector('[aria-hidden="true"]'))
+    expect(screen.getByTestId('conversation-navigator').getAttribute('data-mode')).toBe('edge')
+    expect(markerBars.every((bar) => bar?.className.includes('w-1.5'))).toBe(true)
+    expect(markerBars.every((bar) => bar?.className.includes('group-hover:w-3'))).toBe(true)
   })
 
   it('shows the preview on hover or focus and navigates on click', () => {
@@ -111,6 +161,7 @@ describe('ConversationNavigator', () => {
     }
     render(
       <ConversationNavigator
+        mode="full"
         items={[item]}
         activeItemId="user-1"
         onNavigate={onNavigate}
diff --git a/desktop/src/components/chat/ConversationNavigator.tsx b/desktop/src/components/chat/ConversationNavigator.tsx
index 59919ec5..2c703118 100644
--- a/desktop/src/components/chat/ConversationNavigator.tsx
+++ b/desktop/src/components/chat/ConversationNavigator.tsx
@@ -19,6 +19,34 @@ export type ConversationNavigationItem = {
   attachmentCount: number
 }
 
+export type ConversationNavigationMode = 'full' | 'compact' | 'edge'
+
+const NAVIGATION_MODE_STYLES: Record<ConversationNavigationMode, {
+  position: string
+  lane: string
+  button: string
+  marker: string
+}> = {
+  full: {
+    position: 'left-2',
+    lane: 'w-10',
+    button: 'w-10 pl-1.5',
+    marker: 'w-3 group-hover:w-5 group-focus-visible:w-5',
+  },
+  compact: {
+    position: 'left-1',
+    lane: 'w-7',
+    button: 'w-7 pl-1',
+    marker: 'w-2.5 group-hover:w-4 group-focus-visible:w-4',
+  },
+  edge: {
+    position: 'left-0',
+    lane: 'w-5',
+    button: 'w-5 pl-0.5',
+    marker: 'w-1.5 group-hover:w-3 group-focus-visible:w-3',
+  },
+}
+
 function normalizePreview(content: string) {
   const normalized = content.slice(0, 2_000)
     .replace(/\[([^\]]+)]\([^)]+\)/g, '$1')
@@ -51,10 +79,12 @@ export function buildConversationNavigationItems(
 }
 
 export function ConversationNavigator({
+  mode,
   items,
   activeItemId,
   onNavigate,
 }: {
+  mode: ConversationNavigationMode
   items: ConversationNavigationItem[]
   activeItemId: string | null
   onNavigate: (item: ConversationNavigationItem) => void
@@ -64,6 +94,7 @@ export function ConversationNavigator({
   const [previewPosition, setPreviewPosition] = useState({ left: 0, top: 0 })
   const markerRefs = useRef(new Map<string, HTMLButtonElement>())
   const previewItem = items.find((item) => item.id === previewItemId) ?? null
+  const modeStyles = NAVIGATION_MODE_STYLES[mode]
 
   const openPreview = (itemId: string, marker: HTMLButtonElement) => {
     const rect = marker.getBoundingClientRect()
@@ -82,10 +113,11 @@ export function ConversationNavigator({
   return (
     <nav
       data-testid="conversation-navigator"
+      data-mode={mode}
       aria-label={t('chat.conversationNavigator.label')}
-      className="absolute left-2 top-1/2 z-30 flex max-h-[64%] -translate-y-1/2 flex-col overflow-visible"
+      className={`absolute top-1/2 z-30 flex max-h-[64%] -translate-y-1/2 flex-col overflow-visible ${modeStyles.position}`}
     >
-      <div className="conversation-navigation-scroll flex max-h-full w-10 flex-col items-start gap-0.5 overflow-y-auto py-2 [scrollbar-width:none] [&::-webkit-scrollbar]:hidden">
+      <div className={`conversation-navigation-scroll flex max-h-full flex-col items-start gap-0.5 overflow-y-auto py-2 [scrollbar-width:none] [&::-webkit-scrollbar]:hidden ${modeStyles.lane}`}>
         {items.map((item) => {
           const roleLabel = item.role === 'user'
             ? t('chat.userMessageReference')
@@ -111,17 +143,18 @@ export function ConversationNavigator({
                 onFocus={(event) => openPreview(item.id, event.currentTarget)}
                 onBlur={() => setPreviewItemId(null)}
                 onClick={() => onNavigate(item)}
-                className="group flex h-4 w-10 items-center rounded-sm pl-1.5 focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-[var(--color-brand)]/35"
+                className={`group flex h-4 items-center rounded-sm focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-[var(--color-brand)]/35 ${modeStyles.button}`}
               >
                 <span
                   aria-hidden="true"
                   className={[
-                    'block h-0.5 rounded-full transition-[width,background-color,opacity] duration-150',
+                    'block h-0.5 rounded-full transition-[width,background-color,opacity] duration-200 ease-out motion-reduce:transition-none',
+                    modeStyles.marker,
                     isActive
-                      ? 'w-5 bg-[var(--color-brand)] opacity-100'
+                      ? 'bg-[var(--color-brand)] opacity-100'
                       : item.role === 'user'
-                        ? 'w-4 bg-[var(--color-text-secondary)] opacity-75 group-hover:w-5 group-hover:bg-[var(--color-text-primary)] group-hover:opacity-100'
-                        : 'w-2.5 bg-[var(--color-outline)] opacity-65 group-hover:w-4 group-hover:bg-[var(--color-text-secondary)] group-hover:opacity-100',
+                        ? 'bg-[var(--color-text-secondary)] opacity-75 group-hover:bg-[var(--color-text-primary)] group-hover:opacity-100 group-focus-visible:bg-[var(--color-text-primary)] group-focus-visible:opacity-100'
+                        : 'bg-[var(--color-outline)] opacity-65 group-hover:bg-[var(--color-text-secondary)] group-hover:opacity-100 group-focus-visible:bg-[var(--color-text-secondary)] group-focus-visible:opacity-100',
                   ].join(' ')}
                 />
               </button>
diff --git a/desktop/src/components/chat/MessageList.test.tsx b/desktop/src/components/chat/MessageList.test.tsx
index ea319f27..8a60770c 100644
--- a/desktop/src/components/chat/MessageList.test.tsx
+++ b/desktop/src/components/chat/MessageList.test.tsx
@@ -350,7 +350,7 @@ describe('MessageList nested tool calls', () => {
     expect(screen.getByText('latest assistant reply')).toBeTruthy()
   })
 
-  it('shows the conversation navigator for normal desktop transcripts and hides it in compact mode', () => {
+  it('keeps the conversation navigator available in compact desktop transcripts', () => {
     useChatStore.setState({
       sessions: {
         [ACTIVE_TAB]: makeSessionState({
@@ -368,7 +368,72 @@ describe('MessageList nested tool calls', () => {
     expect(screen.getByRole('navigation', { name: 'Conversation navigation' })).toBeTruthy()
 
     rerender(<MessageList compact />)
-    expect(screen.queryByRole('navigation', { name: 'Conversation navigation' })).toBeNull()
+    expect(screen.getByRole('navigation', { name: 'Conversation navigation' })).toBeTruthy()
+  })
+
+  it('adapts the conversation navigator when the chat column is resized by adjacent panels', () => {
+    const observers: Array<{
+      callback: ResizeObserverCallback
+      targets: Element[]
+    }> = []
+    class TestResizeObserver {
+      targets: Element[] = []
+      observe = vi.fn((target: Element) => {
+        this.targets.push(target)
+      })
+      unobserve = vi.fn()
+      disconnect = vi.fn()
+
+      constructor(callback: ResizeObserverCallback) {
+        observers.push({ callback, targets: this.targets })
+      }
+    }
+    vi.stubGlobal('ResizeObserver', TestResizeObserver)
+
+    useChatStore.setState({
+      sessions: {
+        [ACTIVE_TAB]: makeSessionState({
+          messages: [
+            { id: 'user-1', type: 'user_text', content: 'First prompt', timestamp: 1 },
+            { id: 'assistant-1', type: 'assistant_text', content: 'First answer', timestamp: 2 },
+            { id: 'user-2', type: 'user_text', content: 'Second prompt', timestamp: 3 },
+            { id: 'assistant-2', type: 'assistant_text', content: 'Second answer', timestamp: 4 },
+          ],
+        }),
+      },
+    })
+
+    render(<MessageList />)
+    const messageList = screen.getByTestId('message-list')
+    const scroller = messageList.querySelector('.chat-scroll-area') as HTMLElement
+    const layoutObserver = observers.find(({ targets }) => targets.includes(messageList))
+    expect(layoutObserver).toBeTruthy()
+    expect(screen.getByTestId('conversation-navigator').getAttribute('data-mode')).toBe('full')
+
+    const resizeTo = (width: number) => {
+      act(() => {
+        layoutObserver?.callback([{
+          target: messageList,
+          contentRect: { width },
+        } as unknown as ResizeObserverEntry], {} as ResizeObserver)
+      })
+    }
+
+    resizeTo(900)
+    expect(screen.getByTestId('conversation-navigator').getAttribute('data-mode')).toBe('compact')
+    expect(scroller.className.split(/\s+/)).toContain('pl-9')
+
+    resizeTo(640)
+    expect(screen.getByTestId('conversation-navigator').getAttribute('data-mode')).toBe('compact')
+
+    resizeTo(520)
+    expect(screen.getByTestId('conversation-navigator').getAttribute('data-mode')).toBe('edge')
+    expect(scroller.className.split(/\s+/)).toContain('pl-6')
+
+    resizeTo(1000)
+    expect(screen.getByTestId('conversation-navigator').getAttribute('data-mode')).toBe('full')
+    expect(scroller.className.split(/\s+/)).not.toContain('pl-9')
+    expect(scroller.className.split(/\s+/)).not.toContain('pl-6')
   })
 
   it('updates the active conversation marker while the transcript scrolls', () => {
diff --git a/desktop/src/components/chat/MessageList.tsx b/desktop/src/components/chat/MessageList.tsx
index e15e158e..7b933643 100644
--- a/desktop/src/components/chat/MessageList.tsx
+++ b/desktop/src/components/chat/MessageList.tsx
@@ -27,6 +27,7 @@ import {
   buildConversationNavigationItems,
   ConversationNavigator,
   type ConversationNavigationItem,
+  type ConversationNavigationMode,
 } from './ConversationNavigator'
 import type { AgentTaskNotification, UIMessage } from '../../types/chat'
 import { formatTokenCount } from '../../lib/formatTokenCount'
@@ -952,6 +953,8 @@ const VIRTUAL_MAX_ITEM_HEIGHT = 24_000
 const CONTENT_RESIZE_FOLLOW_MIN_DELTA_PX = 2
 const USER_SCROLL_INTENT_WINDOW_MS = 500
 const CONVERSATION_NAVIGATION_MIN_ITEMS = 4
+const CONVERSATION_NAVIGATION_FULL_MIN_WIDTH_PX = 960
+const CONVERSATION_NAVIGATION_COMPACT_MIN_WIDTH_PX = 560
 const STREAMING_ASSISTANT_NAVIGATION_KEY = 'streaming-assistant-message'
 const EMPTY_MESSAGES: UIMessage[] = []
 const EMPTY_AGENT_TASK_NOTIFICATIONS: Record<string, AgentTaskNotification> = {}
@@ -1466,6 +1469,7 @@ export function MessageList({ sessionId, compact = false }: MessageListProps = {
     chatState === 'tool_executing' ||
     hasPendingPermissionCard ||
     (chatState === 'thinking' && Boolean(activeThinkingId))
+  const messageListRef = useRef<HTMLDivElement>(null)
   const scrollContainerRef = useRef<HTMLDivElement>(null)
   const scrollContentRef = useRef<HTMLDivElement>(null)
   const virtualItemHeightsRef = useRef<Map<string, number>>(
@@ -1503,6 +1507,7 @@ export function MessageList({ sessionId, compact = false }: MessageListProps = {
   })
   const [measuredItemsVersion, setMeasuredItemsVersion] = useState(0)
   const [highlightedNavigationItemKey, setHighlightedNavigationItemKey] = useState<string | null>(null)
+  const [messageListWidth, setMessageListWidth] = useState<number | null>(null)
   const branchActionsDisabled =
     isMemberSession ||
     chatState !== 'idle' ||
@@ -1526,6 +1531,27 @@ export function MessageList({ sessionId, compact = false }: MessageListProps = {
     }
   }, [])
 
+  useLayoutEffect(() => {
+    const messageList = messageListRef.current
+    if (!messageList) return
+
+    const updateWidth = (width: number) => {
+      const roundedWidth = Math.round(width)
+      if (roundedWidth <= 0) return
+      setMessageListWidth((current) => current === roundedWidth ? current : roundedWidth)
+    }
+
+    updateWidth(messageList.getBoundingClientRect().width || messageList.clientWidth)
+    if (typeof ResizeObserver === 'undefined') return
+
+    const observer = new ResizeObserver((entries) => {
+      const entry = entries.find((candidate) => candidate.target === messageList)
+      if (entry) updateWidth(entry.contentRect.width)
+    })
+    observer.observe(messageList)
+    return () => observer.disconnect()
+  }, [])
+
   const syncVirtualViewportFromContainer = useCallback((container: HTMLElement) => {
     const nextScrollTop = container.scrollTop
     const nextViewportHeight = container.clientHeight || VIRTUAL_DEFAULT_VIEWPORT_HEIGHT
@@ -1920,10 +1946,26 @@ export function MessageList({ sessionId, compact = false }: MessageListProps = {
     ),
     [conversationNavigationItems, virtualTranscriptWindow.offsets, virtualViewport],
   )
+  const conversationNavigationMode: ConversationNavigationMode =
+    messageListWidth === null || messageListWidth >= CONVERSATION_NAVIGATION_FULL_MIN_WIDTH_PX
+      ? 'full'
+      : messageListWidth >= CONVERSATION_NAVIGATION_COMPACT_MIN_WIDTH_PX
+        ? 'compact'
+        : 'edge'
   const showConversationNavigator =
-    !compact &&
     !isTouchH5Document() &&
     conversationNavigationItems.length >= CONVERSATION_NAVIGATION_MIN_ITEMS
+  const chatScrollPaddingClass = compact
+    ? showConversationNavigator && conversationNavigationMode === 'compact'
+      ? 'pb-5 pl-9 pr-3 py-3'
+      : showConversationNavigator && conversationNavigationMode === 'edge'
+        ? 'pb-5 pl-6 pr-3 py-3'
+        : 'px-3 py-3 pb-5'
+    : showConversationNavigator && conversationNavigationMode === 'compact'
+      ? 'pl-9 pr-4 py-4'
+      : showConversationNavigator && conversationNavigationMode === 'edge'
+        ? 'pl-6 pr-4 py-4'
+        : 'px-4 py-4'
   const confirmTurnCard = useMemo(
     () => visibleTurnChangeCards.find((card) => card.target.messageId === turnUndoConfirmTargetId) ?? null,
     [turnUndoConfirmTargetId, visibleTurnChangeCards],
@@ -2331,7 +2373,7 @@ export function MessageList({ sessionId, compact = false }: MessageListProps = {
   }
 
   return (
-    <div className="relative min-h-0 flex-1">
+    <div ref={messageListRef} data-testid="message-list" className="relative min-h-0 flex-1">
       <div
         ref={scrollContainerRef}
         onScroll={updateAutoScrollState}
@@ -2339,7 +2381,7 @@ export function MessageList({ sessionId, compact = false }: MessageListProps = {
         onPointerDown={markUserScrollIntent}
         onTouchStart={markUserScrollIntent}
         onKeyDown={handleKeyDownScrollIntent}
-        className={`${CHAT_SCROLL_AREA_CLASS} h-full overflow-y-auto ${compact ? 'px-3 py-3 pb-5' : 'px-4 py-4'}`}
+        className={`${CHAT_SCROLL_AREA_CLASS} h-full overflow-y-auto ${chatScrollPaddingClass}`}
       >
         <div
           ref={scrollContentRef}
@@ -2410,6 +2452,7 @@ export function MessageList({ sessionId, compact = false }: MessageListProps = {
 
       {showConversationNavigator ? (
         <ConversationNavigator
+          mode={conversationNavigationMode}
           items={conversationNavigationItems}
           activeItemId={activeConversationNavigationItemId}
           onNavigate={handleNavigateToConversationItem}