diff --git a/.github/pr-evidence/ui-scale-100.png b/.github/pr-evidence/ui-scale-100.png
new file mode 100644
index 00000000..ec326216
Binary files /dev/null and b/.github/pr-evidence/ui-scale-100.png differ
diff --git a/.github/pr-evidence/ui-scale-80.png b/.github/pr-evidence/ui-scale-80.png
new file mode 100644
index 00000000..b8cb602a
Binary files /dev/null and b/.github/pr-evidence/ui-scale-80.png differ
diff --git a/packages/electron/main.mjs b/packages/electron/main.mjs
index fa027314..7285e9a1 100644
--- a/packages/electron/main.mjs
+++ b/packages/electron/main.mjs
@@ -2413,6 +2413,13 @@ const getMenuTargetWindow = () => {
 
 const dispatchMenuAction = (action) => {
   const target = getMenuTargetWindow();
+  // Zoom actions are consumed by the renderer's DOM listener. Sending them
+  // through both the IPC bridge and the DOM event would invoke the handler
+  // multiple times because preload fans the IPC event back into both paths.
+  if (action === 'zoom-in' || action === 'zoom-out' || action === 'zoom-reset') {
+    dispatchDomEventToWindow(target, 'openchamber:menu-action', action);
+    return;
+  }
   emitToWindow(target, 'openchamber:menu-action', action);
   dispatchDomEventToWindow(target, 'openchamber:menu-action', action);
 };
@@ -4963,6 +4970,10 @@ const buildMacMenu = () => {
         { role: 'minimize' },
         { role: 'zoom' },
         { type: 'separator' },
+        { label: 'Zoom In', accelerator: 'CmdOrCtrl+=', click: () => dispatchAction('zoom-in') },
+        { label: 'Zoom Out', accelerator: 'CmdOrCtrl+-', click: () => dispatchAction('zoom-out') },
+        { label: 'Reset Zoom', accelerator: 'CmdOrCtrl+0', click: () => dispatchAction('zoom-reset') },
+        { type: 'separator' },
         { role: 'close' },
       ],
     },
@@ -5076,6 +5087,9 @@ const buildAutoHiddenMenu = () => {
       label: 'Window',
       submenu: [
         { role: 'minimize' },
+        { label: 'Zoom In', accelerator: 'Ctrl+=', click: () => dispatchAction('zoom-in') },
+        { label: 'Zoom Out', accelerator: 'Ctrl+-', click: () => dispatchAction('zoom-out') },
+        { label: 'Reset Zoom', accelerator: 'Ctrl+0', click: () => dispatchAction('zoom-reset') },
         { role: 'togglefullscreen' },
         { type: 'separator' },
         { role: 'close' },
diff --git a/packages/ui/src/components/browser/BrowserPane.tsx b/packages/ui/src/components/browser/BrowserPane.tsx
index 638b9547..216f9448 100644
--- a/packages/ui/src/components/browser/BrowserPane.tsx
+++ b/packages/ui/src/components/browser/BrowserPane.tsx
@@ -588,6 +588,20 @@ const WebviewBrowser: React.FC<BrowserPaneProps> = ({ initialUrl, directory, tab
     }
   }, []);
 
+  React.useEffect(() => {
+    const handleZoom = (event: Event) => {
+      if (!(event instanceof CustomEvent)) return;
+      const action = event.detail;
+      const webview = webviewRef.current;
+      if (!webview || document.activeElement !== webview) return;
+      if (action === 'zoom-in') applyZoom(zoomLevel + ZOOM_STEP);
+      else if (action === 'zoom-out') applyZoom(zoomLevel - ZOOM_STEP);
+      else if (action === 'zoom-reset') applyZoom(0);
+    };
+    window.addEventListener('openchamber:zoom', handleZoom);
+    return () => window.removeEventListener('openchamber:zoom', handleZoom);
+  }, [applyZoom, zoomLevel]);
+
   const clearBrowsingData = React.useCallback((what: 'cookies' | 'cache') => {
     void invokeDesktopCommand('desktop_browser_clear_data', {
       partition: BROWSER_PARTITION,
diff --git a/packages/ui/src/components/chat/DraftPresetChips.tsx b/packages/ui/src/components/chat/DraftPresetChips.tsx
index 31230b64..0b5bd058 100644
--- a/packages/ui/src/components/chat/DraftPresetChips.tsx
+++ b/packages/ui/src/components/chat/DraftPresetChips.tsx
@@ -94,7 +94,7 @@ const SortableChip: React.FC<{
                 {...attributes}
                 {...listeners}
                 onClick={() => onSubmit(item)}
-                className="group inline-flex touch-none select-none items-center gap-1.5 rounded-full border px-3 py-1.5 text-sm text-muted-foreground transition-colors hover:bg-[var(--interactive-hover)] hover:text-foreground"
+                className="group inline-flex touch-none select-none items-center gap-1.5 rounded-full border px-3 py-1.5 typography-ui-label text-muted-foreground transition-colors hover:bg-[var(--interactive-hover)] hover:text-foreground"
                 style={chipStyle}
                 title={item.shared ? t('chat.draftStarters.sharedTitle') : undefined}
             >
diff --git a/packages/ui/src/components/chat/composer/ui/DraftTargetSelectors.tsx b/packages/ui/src/components/chat/composer/ui/DraftTargetSelectors.tsx
index abccd7d6..5b4c6d29 100644
--- a/packages/ui/src/components/chat/composer/ui/DraftTargetSelectors.tsx
+++ b/packages/ui/src/components/chat/composer/ui/DraftTargetSelectors.tsx
@@ -310,7 +310,7 @@ export function DraftTargetSelectors(props: DraftTargetProps) {
                 >
                     <span className="flex min-w-0 items-center gap-1.5">
                         {selectedProject.kind === 'chat'
-                            ? <span className="truncate">{t('chat.chatInput.chooseProject')}</span>
+                            ? <span className="truncate typography-ui-label">{t('chat.chatInput.chooseProject')}</span>
                             : <ProjectLabel project={selectedProject} theme={theme} />}
                         <Icon name="arrow-down-s" className="size-4 shrink-0 opacity-50" />
                     </span>
@@ -498,7 +498,7 @@ export function MobileDraftTargetTriggers(
                 onClick={() => onOpenPicker('project')}
             >
                 {selectedProject.kind === 'chat'
-                    ? <span className="truncate">{t('chat.chatInput.chooseProject')}</span>
+                        ? <span className="truncate typography-ui-label">{t('chat.chatInput.chooseProject')}</span>
                     : <ProjectLabel project={selectedProject} theme={theme} />}
                 <Icon name="arrow-down-s" className="h-3.5 w-3.5 flex-shrink-0 text-muted-foreground" />
             </button>
diff --git a/packages/ui/src/components/layout/ContextPanel.tsx b/packages/ui/src/components/layout/ContextPanel.tsx
index 0b7eef5d..ed8de6ba 100644
--- a/packages/ui/src/components/layout/ContextPanel.tsx
+++ b/packages/ui/src/components/layout/ContextPanel.tsx
@@ -52,7 +52,7 @@ import {
 import { getContextSurfaceWidthFraction } from '@/lib/surfaces/registry';
 import { isTerminalEventTarget } from '@/lib/terminalFocus';
 
-const CONTEXT_PANEL_MIN_WIDTH = 380;
+const CONTEXT_PANEL_MIN_WIDTH = 320;
 const CONTEXT_PANEL_MAX_WIDTH = 1400;
 const CONTEXT_PANEL_DEFAULT_WIDTH = 600;
 const RESIZE_FOLLOW_INTERVAL_MS = 100;
@@ -484,10 +484,21 @@ export const ContextPanel: React.FC = () => {
   const [availablePanelAreaWidth, setAvailablePanelAreaWidth] = React.useState<number | null>(null);
   const activeModeForWidth = activeTab?.mode ?? null;
   const manualWidth = activeModeForWidth ? panelState?.widthByMode?.[activeModeForWidth] : undefined;
+  const manualWidthFraction = activeModeForWidth ? panelState?.widthFractionByMode?.[activeModeForWidth] : undefined;
   const widthFraction = activeModeForWidth ? getContextSurfaceWidthFraction(activeModeForWidth) : 0.5;
   const widthFallbackBase = availablePanelAreaWidth
     ?? (typeof window !== 'undefined' ? window.innerWidth : CONTEXT_PANEL_DEFAULT_WIDTH * 2);
-  const width = clampWidth(manualWidth ?? Math.round(widthFraction * widthFallbackBase));
+  const effectiveManualWidth = manualWidthFraction != null && availablePanelAreaWidth != null
+    ? Math.round(manualWidthFraction * availablePanelAreaWidth)
+    : manualWidth;
+  const width = clampWidth(effectiveManualWidth ?? Math.round(widthFraction * widthFallbackBase));
+
+  // Convert legacy pixel-only preferences to a ratio the first time the
+  // available area is known, so existing users also get responsive sizing.
+  React.useEffect(() => {
+    if (!directoryKey || !activeModeForWidth || manualWidthFraction != null || manualWidth == null || availablePanelAreaWidth == null) return;
+    setContextPanelWidth(directoryKey, activeModeForWidth, manualWidth, availablePanelAreaWidth);
+  }, [activeModeForWidth, availablePanelAreaWidth, directoryKey, manualWidth, manualWidthFraction, setContextPanelWidth]);
   const chatSessionIDs = React.useMemo(() => {
     const ids: string[] = [];
     for (const tab of tabs) {
@@ -592,6 +603,7 @@ export const ContextPanel: React.FC = () => {
     // Apply the final width once, letting the regular 200ms width transition
     // carry the panel to the release position.
     const finalWidth = clampWidthForDrag(resizingWidthRef.current ?? width);
+    const availableWidth = resizeAvailableWidthRef.current;
     resizingWidthRef.current = null;
     resizeAvailableWidthRef.current = null;
     if (resizeFollowTimerRef.current !== null) {
@@ -600,7 +612,7 @@ export const ContextPanel: React.FC = () => {
     }
     document.documentElement.style.cursor = '';
     if (directoryKey && activeModeForWidth) {
-      setContextPanelWidth(directoryKey, activeModeForWidth, finalWidth);
+      setContextPanelWidth(directoryKey, activeModeForWidth, finalWidth, availableWidth ?? undefined);
     }
     setIsResizing(false);
     activeResizePointerIDRef.current = null;
diff --git a/packages/ui/src/components/layout/Header.tsx b/packages/ui/src/components/layout/Header.tsx
index 3f2af834..bcca36af 100644
--- a/packages/ui/src/components/layout/Header.tsx
+++ b/packages/ui/src/components/layout/Header.tsx
@@ -1076,7 +1076,9 @@ export const Header: React.FC = () => {
   // `--oc-titlebar-left-inset` so the sidebar strip can mirror it.
   const titlebarLeftInset = React.useMemo(() => {
     if (isDesktopApp && isMacPlatform && !isDesktopWindowFullscreen) {
-      return '5.5rem';
+      // Native traffic lights have a fixed physical footprint. Keep this
+      // clearance in pixels so shrinking the interface cannot overlap them.
+      return '88px';
     }
     if (isTabletStandalonePwa) {
       return 'max(calc(0.75rem + var(--oc-wco-left-inset, 0px)), 5.5rem)';
@@ -1170,8 +1172,10 @@ export const Header: React.FC = () => {
       // Left inset is handled by the no-drag spacer (see renderDesktop); only
       // the right inset / titlebar height are owned by the window-controls overlay.
       paddingRight: 'calc(0.75rem + var(--oc-wco-right-inset, 0px))',
-      minHeight: 'max(3rem, var(--oc-wco-titlebar-height, 0px))',
-      height: 'max(3rem, var(--oc-wco-titlebar-height, 0px))',
+      // Keep the titlebar safe area in physical pixels. Interface zoom may
+      // shrink rem content, but native macOS traffic lights must never overlap it.
+      minHeight: 'max(56px, var(--oc-wco-titlebar-height, 0px))',
+      height: 'max(56px, var(--oc-wco-titlebar-height, 0px))',
     };
   }, [isDesktopApp, isVSCode, usesFramelessChrome, windowControlsSide]);
 
diff --git a/packages/ui/src/components/layout/Sidebar.tsx b/packages/ui/src/components/layout/Sidebar.tsx
index 77a7b32d..f18d3a3a 100644
--- a/packages/ui/src/components/layout/Sidebar.tsx
+++ b/packages/ui/src/components/layout/Sidebar.tsx
@@ -6,7 +6,7 @@ import { useUIStore } from '@/stores/useUIStore';
 import { ScrollableOverlay } from '@/components/ui/ScrollableOverlay';
 
 const SIDEBAR_CONTENT_WIDTH = 280;
-const SIDEBAR_MIN_WIDTH = 280;
+const SIDEBAR_MIN_WIDTH = 168;
 const SIDEBAR_MAX_WIDTH = 500;
 
 interface SidebarProps {
diff --git a/packages/ui/src/components/mini-chat/MiniChatLayout.tsx b/packages/ui/src/components/mini-chat/MiniChatLayout.tsx
index 84afce61..58883fb5 100644
--- a/packages/ui/src/components/mini-chat/MiniChatLayout.tsx
+++ b/packages/ui/src/components/mini-chat/MiniChatLayout.tsx
@@ -264,7 +264,8 @@ const MiniChatHeader: React.FC<{ mode: MiniChatMode }> = ({ mode }) => {
       className={cn(
         'flex items-center gap-3 bg-background',
         usesFramelessChrome && windowControlsSide === 'right' ? 'pr-0' : 'pr-3',
-        hasMacTrafficLights ? 'pl-[5.5rem]' : 'pl-3',
+        // Native traffic lights are fixed-size OS chrome, not scaled UI.
+        hasMacTrafficLights ? 'pl-[88px]' : 'pl-3',
         usesFramelessChrome ? 'h-12' : macosHeaderSizeClass || 'min-h-14',
       )}
       style={dragRegionStyle}
diff --git a/packages/ui/src/components/multirun/MultiRunLauncher.tsx b/packages/ui/src/components/multirun/MultiRunLauncher.tsx
index 36323a3b..7543588a 100644
--- a/packages/ui/src/components/multirun/MultiRunLauncher.tsx
+++ b/packages/ui/src/components/multirun/MultiRunLauncher.tsx
@@ -208,7 +208,7 @@ export const MultiRunLauncher: React.FC<MultiRunLauncherProps> = ({
   const desktopHeaderPaddingClass = React.useMemo(() => {
     if ((isDesktopApp && isMacPlatform) || isTabletStandalonePwa) {
       // Match main app header: reserve space for Mac/iPadOS traffic lights.
-      return 'pl-[5.5rem]';
+      return 'pl-[88px]';
     }
     return 'pl-3';
   }, [isDesktopApp, isMacPlatform, isTabletStandalonePwa]);
diff --git a/packages/ui/src/components/providers/ThemeProvider.tsx b/packages/ui/src/components/providers/ThemeProvider.tsx
index 918aa272..3086bab0 100644
--- a/packages/ui/src/components/providers/ThemeProvider.tsx
+++ b/packages/ui/src/components/providers/ThemeProvider.tsx
@@ -1,4 +1,5 @@
 import React from 'react';
+import { isTerminalEventTarget } from '@/lib/terminalFocus';
 import { useUIStore } from '@/stores/useUIStore';
 
 interface ThemeProviderProps {
@@ -16,5 +17,32 @@ export const ThemeProvider: React.FC<ThemeProviderProps> = ({ children }) => {
     applyPadding();
   }, [fontSize, applyTypography, padding, applyPadding]);
 
+  React.useEffect(() => {
+    const handleZoom = (event: Event) => {
+      if (!(event instanceof CustomEvent)) return;
+      const action = event.detail;
+      if (action !== 'zoom-in' && action !== 'zoom-out' && action !== 'zoom-reset') return;
+      const active = document.activeElement;
+      if (active?.tagName === 'WEBVIEW' || active?.closest('webview')) return;
+      const state = useUIStore.getState();
+      const isTerminal = isTerminalEventTarget(active)
+        || active?.matches('[data-terminal-hidden-input="true"]') === true;
+      const isEditor = active?.closest('.cm-editor') != null;
+      if (action === 'zoom-reset') {
+        if (isTerminal) state.setTerminalFontSize(14);
+        else if (isEditor) state.setEditorFontSize(13);
+        else state.setFontSize(100);
+      } else if (isTerminal) {
+        state.setTerminalFontSize(state.terminalFontSize + (action === 'zoom-in' ? 1 : -1));
+      } else if (isEditor) {
+        state.setEditorFontSize(state.editorFontSize + (action === 'zoom-in' ? 1 : -1));
+      } else {
+        state.setFontSize(state.fontSize + (action === 'zoom-in' ? 10 : -10));
+      }
+    };
+    window.addEventListener('openchamber:zoom', handleZoom);
+    return () => window.removeEventListener('openchamber:zoom', handleZoom);
+  }, []);
+
   return <>{children}</>;
 };
diff --git a/packages/ui/src/components/session/SessionSwitcherDropdown.tsx b/packages/ui/src/components/session/SessionSwitcherDropdown.tsx
index 0cfba1ec..35cc65e4 100644
--- a/packages/ui/src/components/session/SessionSwitcherDropdown.tsx
+++ b/packages/ui/src/components/session/SessionSwitcherDropdown.tsx
@@ -143,7 +143,7 @@ function SwitcherContent({ onSelect, variant, scopeProjectId }: SwitcherContentP
           )}
         >
           <Icon name="chat-new" className="h-4 w-4 flex-shrink-0 text-muted-foreground" />
-          <span className="truncate text-[14px] font-normal leading-tight text-foreground">
+          <span className="truncate typography-ui-label font-normal leading-tight text-foreground">
             {t('sessions.sidebar.header.actions.newSession')}
           </span>
         </BaseMenu.Item>
@@ -293,7 +293,7 @@ function SwitcherRow({ session, depth, variant, secondaryMeta, hasChildren, isEx
               {isExpanded ? <Icon name="arrow-down-s" className="h-3.5 w-3.5" /> : <Icon name="arrow-right-s" className="h-3.5 w-3.5" />}
             </span>
           ) : null}
-          <span className={cn('truncate text-[14px] font-normal leading-tight', isActive ? 'text-primary' : 'text-foreground')}>
+          <span className={cn('truncate typography-ui-label font-normal leading-tight', isActive ? 'text-primary' : 'text-foreground')}>
             {sessionTitle}
           </span>
         </div>
diff --git a/packages/ui/src/components/session/sidebar/projects/SessionGroupSection.tsx b/packages/ui/src/components/session/sidebar/projects/SessionGroupSection.tsx
index e92a9d2b..f1e85efd 100644
--- a/packages/ui/src/components/session/sidebar/projects/SessionGroupSection.tsx
+++ b/packages/ui/src/components/session/sidebar/projects/SessionGroupSection.tsx
@@ -1146,7 +1146,7 @@ function SessionGroupSectionBase(props: SessionGroupSectionProps): React.ReactNo
           {...(dragHandleProps?.listeners ?? {})}
         >
           <div className="min-w-0 flex flex-1 flex-col justify-center gap-0.5 overflow-hidden">
-            <p className="text-[14px] font-normal truncate text-foreground/92">
+            <p className="typography-ui-label font-normal truncate text-foreground/92">
               {group.isArchivedBucket ? (
                 <span className="inline-flex min-w-0 max-w-full items-center gap-1">
                   <span className="inline-flex h-3.5 w-3.5 shrink-0 items-center justify-center">
diff --git a/packages/ui/src/components/session/sidebar/projects/SessionProjectScroller.tsx b/packages/ui/src/components/session/sidebar/projects/SessionProjectScroller.tsx
index 3e29f58c..68ef5ef2 100644
--- a/packages/ui/src/components/session/sidebar/projects/SessionProjectScroller.tsx
+++ b/packages/ui/src/components/session/sidebar/projects/SessionProjectScroller.tsx
@@ -425,7 +425,7 @@ function SessionProjectScrollerComponent(props: Props): React.ReactNode {
           ) : (
             <>
               <Icon name="history" className="h-3.5 w-3.5 flex-shrink-0 text-muted-foreground/80" />
-              <span className="truncate text-[14px] font-semibold lowercase text-foreground">
+              <span className="truncate typography-ui-label font-semibold lowercase text-foreground">
                 {t('sessions.sidebar.activity.recentTitle')}
               </span>
             </>
diff --git a/packages/ui/src/components/session/sidebar/projects/sortableItems.tsx b/packages/ui/src/components/session/sidebar/projects/sortableItems.tsx
index 00b0ab08..e49593a4 100644
--- a/packages/ui/src/components/session/sidebar/projects/sortableItems.tsx
+++ b/packages/ui/src/components/session/sidebar/projects/sortableItems.tsx
@@ -96,7 +96,7 @@ export const ProjectHeaderIdentity: React.FC<ProjectHeaderIdentityProps> = ({
           <Icon name="folder" className={cn('h-3.5 w-3.5 text-muted-foreground/80', iconVisibilityClassName)} style={iconColor ? { color: iconColor } : undefined} />
         )}
       </span>
-      <span className="truncate text-[14px] font-semibold lowercase text-foreground">{projectLabel}</span>
+      <span className="truncate typography-ui-label font-semibold lowercase text-foreground">{projectLabel}</span>
     </>
   );
 };
diff --git a/packages/ui/src/components/session/sidebar/recent/SidebarActivitySections.tsx b/packages/ui/src/components/session/sidebar/recent/SidebarActivitySections.tsx
index 1f75ff6f..69401ebf 100644
--- a/packages/ui/src/components/session/sidebar/recent/SidebarActivitySections.tsx
+++ b/packages/ui/src/components/session/sidebar/recent/SidebarActivitySections.tsx
@@ -264,7 +264,7 @@ export function SidebarActivitySections(props: Props): React.ReactNode {
                     {isCollapsed ? <Icon name="arrow-right-s" className="h-3.5 w-3.5" /> : <Icon name="arrow-down-s" className="h-3.5 w-3.5" />}
                   </span>
                 </span>
-                <span className="text-[14px] font-semibold lowercase text-foreground">{section.title}</span>
+                <span className="typography-ui-label font-semibold lowercase text-foreground">{section.title}</span>
               </button>
               {section.key === 'chats' && props.onNewChat ? (
                 <button
diff --git a/packages/ui/src/hooks/useMenuActions.ts b/packages/ui/src/hooks/useMenuActions.ts
index dd163593..9d5ee1ea 100644
--- a/packages/ui/src/hooks/useMenuActions.ts
+++ b/packages/ui/src/hooks/useMenuActions.ts
@@ -91,7 +91,10 @@ type MenuAction =
   | 'previous-project'
   | 'next-project'
   | 'help-dialog'
-  | 'download-logs';
+  | 'download-logs'
+  | 'zoom-in'
+  | 'zoom-out'
+  | 'zoom-reset';
 
 export const useMenuActions = (
   onToggleMemoryDebug?: () => void
@@ -270,6 +273,12 @@ export const useMenuActions = (
           break;
         }
 
+        case 'zoom-in':
+        case 'zoom-out':
+        case 'zoom-reset':
+          window.dispatchEvent(new CustomEvent('openchamber:zoom', { detail: action }));
+          break;
+
         case 'theme-light':
           setThemeMode('light');
           break;
diff --git a/packages/ui/src/lib/surfaces/DOCUMENTATION.md b/packages/ui/src/lib/surfaces/DOCUMENTATION.md
index 8ae0254e..64fe0606 100644
--- a/packages/ui/src/lib/surfaces/DOCUMENTATION.md
+++ b/packages/ui/src/lib/surfaces/DOCUMENTATION.md
@@ -15,8 +15,9 @@ edge (`components/layout/ContextPanelRail.tsx`) and rendered by
   rail until a tab of their mode exists, and stay visible for as long as one
   does — they must not disappear while in use.
 - `defaultWidthFraction` is the panel width as a fraction of the content area,
-  used until the user manually resizes that surface (manual widths are stored
-  per mode in `useUIStore.contextPanelByDirectory[dir].widthByMode`).
+  used until the user manually resizes that surface. Manual widths are stored
+  per mode in `useUIStore.contextPanelByDirectory[dir].widthFractionByMode`;
+  the legacy `widthByMode` field is retained only for migration compatibility.
 - Rail order is user-reorderable and persisted globally in
   `useUIStore.contextRailOrder`; `sortContextSurfaces` applies it on top of the
   registry's default order and appends any missing surfaces.
diff --git a/packages/ui/src/stores/useUIStore.contextPanel.test.ts b/packages/ui/src/stores/useUIStore.contextPanel.test.ts
index d934da2d..2e2db9d8 100644
--- a/packages/ui/src/stores/useUIStore.contextPanel.test.ts
+++ b/packages/ui/src/stores/useUIStore.contextPanel.test.ts
@@ -6,6 +6,7 @@ import { useUIStore } from './useUIStore';
 const getContextPanelTabs = (directory: string) => useUIStore.getState().contextPanelByDirectory[directory]?.tabs ?? [];
 
 const getTerminalTab = (directory: string) => getContextPanelTabs(directory).find((tab) => tab.mode === 'terminal');
+const originalPersistOptions = useUIStore.persist.getOptions();
 
 beforeEach(() => {
   useUIStore.setState({ contextPanelByDirectory: {}, contextRailOrder: [] });
@@ -173,6 +174,46 @@ describe('useUIStore context panel tabs', () => {
     expect(tabs.some((tab) => tab.mode === 'plan')).toBe(true);
   });
 
+  test('drops invalid persisted context-panel width fractions', async () => {
+    const directory = '/repo';
+    useUIStore.persist.setOptions({ storage: {
+      getItem: () => ({
+        version: 20,
+        state: {
+          contextPanelByDirectory: {
+            [directory]: {
+              isOpen: true,
+              expanded: false,
+              widthByMode: {},
+              widthFractionByMode: {
+                diff: 0,
+                file: 1.25,
+                context: Number.NaN,
+                plan: '0.4',
+                chat: 0.4,
+              },
+              touchedAt: 1,
+              activeTabId: null,
+              tabs: [],
+            },
+          },
+        },
+      }),
+      setItem: () => undefined,
+      removeItem: () => undefined,
+    } });
+
+    try {
+      useUIStore.setState(useUIStore.getInitialState(), true);
+      await useUIStore.persist.rehydrate();
+
+      const panel = useUIStore.getState().contextPanelByDirectory[directory];
+      expect(panel?.widthFractionByMode).toEqual({ chat: 0.4 });
+    } finally {
+      useUIStore.persist.setOptions(originalPersistOptions);
+    }
+  });
+
   test('drops a persisted saved-plan tab carrying an owner but no plan id', () => {
     const directory = '/repo';
     const persisted = {
@@ -665,9 +706,21 @@ describe('useUIStore per-surface panel widths', () => {
 
     const state = useUIStore.getState().contextPanelByDirectory[directory];
     expect(state?.widthByMode.diff).toBe(700);
-    expect(state?.widthByMode.git).toBe(380);
+    expect(state?.widthByMode.git).toBe(320);
     expect(state?.widthByMode.browser).toBe(undefined);
   });
+
+  test('captures the clamped width as a responsive ratio when the panel area is known', () => {
+    useUIStore.getState().openContextPanelTab(directory, { mode: 'diff' });
+    useUIStore.getState().setContextPanelWidth(directory, 'diff', 100, 1000);
+    useUIStore.getState().setContextPanelWidth(directory, 'git', 700, 1000);
+
+    const state = useUIStore.getState().contextPanelByDirectory[directory];
+    expect(state?.widthByMode.diff).toBe(320);
+    expect(state?.widthFractionByMode.diff).toBe(0.32);
+    expect(state?.widthFractionByMode.git).toBe(0.7);
+    expect(state?.widthFractionByMode.browser).toBe(undefined);
+  });
 });
 
 describe('useUIStore contextRailOrder', () => {
diff --git a/packages/ui/src/stores/useUIStore.ts b/packages/ui/src/stores/useUIStore.ts
index 35e4c141..51d0341d 100644
--- a/packages/ui/src/stores/useUIStore.ts
+++ b/packages/ui/src/stores/useUIStore.ts
@@ -149,6 +149,9 @@ type ContextPanelDirectoryState = {
   // Manual per-surface widths (px), populated only by user resize; surfaces
   // without an entry fall back to their registry defaultWidthFraction.
   widthByMode: Partial<Record<ContextPanelMode, number>>;
+  // Ratios captured when a user resizes a surface. These remain responsive
+  // across window sizes while widthByMode preserves older persisted values.
+  widthFractionByMode: Partial<Record<ContextPanelMode, number>>;
   touchedAt: number;
 };
 
@@ -203,12 +206,12 @@ const isLegacyDefaultTemplates = (value: unknown): boolean => {
 };
 
 const CONTEXT_PANEL_DEFAULT_WIDTH = 380;
-const CONTEXT_PANEL_MIN_WIDTH = 380;
+const CONTEXT_PANEL_MIN_WIDTH = 320;
 const CONTEXT_PANEL_MAX_WIDTH = 1400;
 /** Per surface, not per panel: see clampContextPanelTabs. */
 const CONTEXT_PANEL_MAX_TABS = 12;
 const CONTEXT_PANEL_MAX_LABEL_LENGTH = 120;
-const LEFT_SIDEBAR_MIN_WIDTH = 280;
+const LEFT_SIDEBAR_MIN_WIDTH = 168;
 /** Separates browser tabs opened in the same millisecond. */
 let browserTabSequence = 0;
 
@@ -513,6 +516,7 @@ const touchContextPanelState = (prev?: ContextPanelDirectoryState): ContextPanel
     tabs: [],
     activeTabId: null,
     widthByMode: {},
+    widthFractionByMode: {},
     touchedAt: Date.now(),
   };
 };
@@ -671,6 +675,7 @@ const sanitizeContextPanelByDirectory = (
       tabs?: unknown;
       activeTabId?: unknown;
       widthByMode?: unknown;
+      widthFractionByMode?: unknown;
       touchedAt?: unknown;
       mode?: unknown;
       targetPath?: unknown;
@@ -714,6 +719,20 @@ const sanitizeContextPanelByDirectory = (
         }
       }
     }
+    const widthFractionByMode: Partial<Record<ContextPanelMode, number>> = {};
+    if (candidate.widthFractionByMode && typeof candidate.widthFractionByMode === 'object') {
+      for (const [mode, value] of Object.entries(candidate.widthFractionByMode as Record<string, unknown>)) {
+        if (
+          (mode === 'diff' || mode === 'file' || mode === 'context' || mode === 'plan' || mode === 'chat' || mode === 'browser' || mode === 'git' || mode === 'pr' || mode === 'linear' || mode === 'notes' || mode === 'terminal')
+          && typeof value === 'number'
+          && Number.isFinite(value)
+          && value > 0
+          && value <= 1
+        ) {
+          widthFractionByMode[mode] = value;
+        }
+      }
+    }
 
     next[directory] = {
       isOpen: candidate.isOpen === true,
@@ -721,6 +740,7 @@ const sanitizeContextPanelByDirectory = (
       tabs: clampedTabs,
       activeTabId: resolveActiveContextPanelTabID(clampedTabs, resolvedActiveTabId),
       widthByMode,
+      widthFractionByMode,
       touchedAt: typeof candidate.touchedAt === 'number' && Number.isFinite(candidate.touchedAt)
         ? candidate.touchedAt
         : Date.now(),
@@ -993,7 +1013,7 @@ interface UIStore {
   closeContextPanelTabs: (directory: string, tabIds: readonly string[]) => void;
   closeContextPanel: (directory: string) => void;
   toggleContextPanelExpanded: (directory: string) => void;
-  setContextPanelWidth: (directory: string, mode: ContextPanelMode, width: number) => void;
+  setContextPanelWidth: (directory: string, mode: ContextPanelMode, width: number, availableWidth?: number) => void;
   setNotesPanelHeight: (height: number) => void;
   setWorkStatusSectionExpanded: (sectionId: string, expanded: boolean) => void;
   setWorkStatusScrollTop: (scrollTop: number) => void;
@@ -1741,7 +1761,7 @@ export const useUIStore = create<UIStore>()(
           });
         },
 
-        setContextPanelWidth: (directory, mode, width) => {
+        setContextPanelWidth: (directory, mode, width, availableWidth) => {
           const normalizedDirectory = normalizeDirectoryPath((directory || '').trim());
           if (!normalizedDirectory) {
             return;
@@ -1750,13 +1770,20 @@ export const useUIStore = create<UIStore>()(
           set((state) => {
             const prev = state.contextPanelByDirectory[normalizedDirectory];
             const current = touchContextPanelState(prev);
+            const clampedWidth = clampContextPanelWidth(width);
             const byDirectory = {
               ...state.contextPanelByDirectory,
               [normalizedDirectory]: {
                 ...current,
                 widthByMode: {
                   ...current.widthByMode,
-                  [mode]: clampContextPanelWidth(width),
+                  [mode]: clampedWidth,
+                },
+                widthFractionByMode: {
+                  ...current.widthFractionByMode,
+                  ...(availableWidth && availableWidth > 0
+                    ? { [mode]: Math.min(1, Math.max(0, clampedWidth / availableWidth)) }
+                    : {}),
                 },
               },
             };
@@ -2140,21 +2167,20 @@ export const useUIStore = create<UIStore>()(
 
           const entries = Object.entries(SEMANTIC_TYPOGRAPHY) as Array<[SemanticTypographyKey, string]>;
 
-          // Default must be SEMANTIC_TYPOGRAPHY (from CSS). Remove overrides.
+          // Scale the root rem unit so regular utility classes, icons, spacing,
+          // and semantic typography all respond to the same interface setting.
           if (scale === 1) {
+            root.style.removeProperty('font-size');
             for (const [key] of entries) {
               root.style.removeProperty(getTypographyVariable(key));
             }
             return;
           }
 
-          for (const [key, baseValue] of entries) {
-            const numericValue = parseFloat(baseValue);
-            if (!Number.isFinite(numericValue)) {
-              continue;
-            }
-            root.style.setProperty(getTypographyVariable(key), `${numericValue * scale}rem`);
-          }
+          root.style.fontSize = `${scale * 100}%`;
+
+          // The variables remain authored in rem and inherit the root scale.
+          for (const [key] of entries) root.style.removeProperty(getTypographyVariable(key));
         },
 
         applyPadding: () => {