diff --git a/frontend/src/App.css b/frontend/src/App.css
index 74ad92ec..a1773110 100644
--- a/frontend/src/App.css
+++ b/frontend/src/App.css
@@ -697,5 +697,5 @@ body[data-theme='dark'] .gonavi-query-editor-db-token {
 /* Legacy sidebar resize bounds — mirror v2 .gn-v2-app-sider so Ant Design inline width locks do not collapse drag range. */
 body[data-ui-version="legacy"] .ant-layout-sider {
   min-width: 232px !important;
-  max-width: 420px !important;
+  max-width: min(960px, calc(100vw - 360px)) !important;
 }
diff --git a/frontend/src/App.tool-center.test.ts b/frontend/src/App.tool-center.test.ts
index 32da0f27..6ce7f4ad 100644
--- a/frontend/src/App.tool-center.test.ts
+++ b/frontend/src/App.tool-center.test.ts
@@ -26,6 +26,10 @@ const appSidebarResizeSource = readFileSync(
   fileURLToPath(new globalThis.URL('./hooks/useAppSidebarResize.ts', import.meta.url)),
   'utf8',
 );
+const sidebarLayoutSource = readFileSync(
+  fileURLToPath(new globalThis.URL('./utils/sidebarLayout.ts', import.meta.url)),
+  'utf8',
+);
 
 const getGlobalShortcutCaseBlock = (action: string) => {
   const caseToken = `case '${action}':`;
@@ -285,8 +289,12 @@ describe('tool center menu entries', () => {
     expect(appSidebarResizeSource).toContain('ghostRef.current.style.left = `${startGuideLeft + (newWidth - startWidth)}px`;');
   });
 
-  it('keeps legacy sidebar resize bounds aligned with the v2 sider CSS limits', () => {
-    expect(appCss).toMatch(/body\[data-ui-version="legacy"\]\s+\.ant-layout-sider\s*\{[^}]*min-width:\s*232px\s*!important;[^}]*max-width:\s*420px\s*!important;/s);
+  it('keeps sidebar resize bounds aligned across drag logic and sider CSS limits', () => {
+    expect(sidebarLayoutSource).toContain('export const SIDEBAR_RESIZE_MAX_WIDTH = 960;');
+    expect(sidebarLayoutSource).toContain('export const SIDEBAR_MIN_WORKBENCH_WIDTH = 360;');
+    expect(appSidebarResizeSource).toContain('resolveSidebarResizeMaxWidth(window.innerWidth, minWidth)');
+    expect(appCss).toMatch(/body\[data-ui-version="legacy"\]\s+\.ant-layout-sider\s*\{[^}]*min-width:\s*232px\s*!important;[^}]*max-width:\s*min\(960px,\s*calc\(100vw - 360px\)\)\s*!important;/s);
+    expect(v2ThemeCss).toMatch(/body\[data-ui-version="v2"\]\s+\.gn-v2-app-sider\s*\{[^}]*min-width:\s*232px\s*!important;[^}]*max-width:\s*min\(960px,\s*calc\(100vw - 360px\)\)\s*!important;/s);
   });
 
   it('keeps connection modal warm-mounted while leaving the other heavyweight modals conditional', () => {
diff --git a/frontend/src/hooks/useAppSidebarResize.ts b/frontend/src/hooks/useAppSidebarResize.ts
index fc657dd8..b86f412b 100644
--- a/frontend/src/hooks/useAppSidebarResize.ts
+++ b/frontend/src/hooks/useAppSidebarResize.ts
@@ -1,7 +1,9 @@
 import React, { useRef } from 'react';
-
-const SIDEBAR_RESIZE_MIN_WIDTH = 200;
-const SIDEBAR_RESIZE_MAX_WIDTH = 600;
+import {
+  SIDEBAR_RESIZE_MAX_WIDTH,
+  SIDEBAR_RESIZE_MIN_WIDTH,
+  resolveSidebarResizeMaxWidth,
+} from '../utils/sidebarLayout';
 
 type SidebarResizeBounds = { minWidth: number; maxWidth: number };
 type SidebarResizeDragState = SidebarResizeBounds & {
@@ -23,7 +25,8 @@ const resolveSidebarResizeBounds = (siderElement: Element | null): SidebarResize
   const cssMinWidth = parseCssPixelValue(computed.minWidth);
   const cssMaxWidth = parseCssPixelValue(computed.maxWidth);
   const minWidth = Math.max(SIDEBAR_RESIZE_MIN_WIDTH, cssMinWidth && cssMinWidth > 0 ? cssMinWidth : SIDEBAR_RESIZE_MIN_WIDTH);
-  const maxWidth = Math.max(minWidth, Math.min(SIDEBAR_RESIZE_MAX_WIDTH, cssMaxWidth && cssMaxWidth > 0 ? cssMaxWidth : SIDEBAR_RESIZE_MAX_WIDTH));
+  const viewportMaxWidth = resolveSidebarResizeMaxWidth(window.innerWidth, minWidth);
+  const maxWidth = Math.max(minWidth, Math.min(viewportMaxWidth, cssMaxWidth && cssMaxWidth > 0 ? cssMaxWidth : viewportMaxWidth));
   return { minWidth, maxWidth };
 };
 
diff --git a/frontend/src/store.test.ts b/frontend/src/store.test.ts
index 0648731e..2fd7b942 100644
--- a/frontend/src/store.test.ts
+++ b/frontend/src/store.test.ts
@@ -1,4 +1,5 @@
 import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
+import { SIDEBAR_RESIZE_MAX_WIDTH } from './utils/sidebarLayout';
 
 class MemoryStorage implements Storage {
   private data = new Map<string, string>();
@@ -360,6 +361,30 @@ describe('store appearance persistence', () => {
     expect(appearance.v2SidebarPersistedFilter).toHaveLength(120);
   });
 
+  it('persists wider sidebar widths and clamps oversized restored values', async () => {
+    const { useStore } = await importStore();
+
+    useStore.getState().setSidebarWidth(880);
+    expect(useStore.getState().sidebarWidth).toBe(880);
+
+    let persisted = JSON.parse(storage.getItem('lite-db-storage') || '{}');
+    expect(persisted.state.sidebarWidth).toBe(880);
+
+    useStore.getState().setSidebarWidth(1200);
+    expect(useStore.getState().sidebarWidth).toBe(SIDEBAR_RESIZE_MAX_WIDTH);
+
+    storage.setItem('lite-db-storage', JSON.stringify({
+      state: {
+        sidebarWidth: 1200,
+      },
+      version: 13,
+    }));
+
+    vi.resetModules();
+    const reloaded = await importStore();
+    expect(reloaded.useStore.getState().sidebarWidth).toBe(SIDEBAR_RESIZE_MAX_WIDTH);
+  });
+
   it('persists tab display appearance settings and sanitizes invalid elements', async () => {
     const { useStore } = await importStore();
 
diff --git a/frontend/src/store.ts b/frontend/src/store.ts
index dfcb0b3f..fb7275f8 100644
--- a/frontend/src/store.ts
+++ b/frontend/src/store.ts
@@ -87,6 +87,7 @@ import {
   DEFAULT_QUERY_EDITOR_EDITOR_HEIGHT_RATIO,
   sanitizeQueryEditorEditorHeightRatio,
 } from "./utils/queryEditorSplitLayout";
+import { sanitizeSidebarWidth } from "./utils/sidebarLayout";
 import {
   DEFAULT_SIDEBAR_TABLE_METADATA_FIELDS,
   applySidebarTableMetadataFieldOrder,
@@ -2330,12 +2331,6 @@ const sanitizeWindowState = (
   return "normal";
 };
 
-const sanitizeSidebarWidth = (value: unknown): number => {
-  const parsed = Number(value);
-  if (!Number.isFinite(parsed)) return 330;
-  return Math.max(200, Math.min(600, Math.trunc(parsed)));
-};
-
 const sanitizeWindowBounds = (
   value: unknown,
 ): { width: number; height: number; x: number; y: number } | null => {
@@ -3601,7 +3596,7 @@ export const useStore = create<AppState>()(
       setWindowState: (state) => set({ windowState: state }),
 
       setSidebarWidth: (width) =>
-        set({ sidebarWidth: Math.max(200, Math.min(600, Math.trunc(width))) }),
+        set({ sidebarWidth: sanitizeSidebarWidth(width) }),
 
       // AI actions
       toggleAIPanel: () =>
diff --git a/frontend/src/utils/sidebarLayout.test.ts b/frontend/src/utils/sidebarLayout.test.ts
new file mode 100644
index 00000000..dae8c911
--- /dev/null
+++ b/frontend/src/utils/sidebarLayout.test.ts
@@ -0,0 +1,23 @@
+import { describe, expect, it } from 'vitest';
+import {
+  DEFAULT_SIDEBAR_WIDTH,
+  SIDEBAR_RESIZE_MAX_WIDTH,
+  SIDEBAR_RESIZE_MIN_WIDTH,
+  resolveSidebarResizeMaxWidth,
+  sanitizeSidebarWidth,
+} from './sidebarLayout';
+
+describe('sidebar layout bounds', () => {
+  it('allows wider persisted sidebar widths while keeping invalid values safe', () => {
+    expect(sanitizeSidebarWidth(880)).toBe(880);
+    expect(sanitizeSidebarWidth(1200)).toBe(SIDEBAR_RESIZE_MAX_WIDTH);
+    expect(sanitizeSidebarWidth(120)).toBe(SIDEBAR_RESIZE_MIN_WIDTH);
+    expect(sanitizeSidebarWidth('bad')).toBe(DEFAULT_SIDEBAR_WIDTH);
+  });
+
+  it('keeps enough workbench space when resolving drag width on smaller windows', () => {
+    expect(resolveSidebarResizeMaxWidth(1600)).toBe(SIDEBAR_RESIZE_MAX_WIDTH);
+    expect(resolveSidebarResizeMaxWidth(1180)).toBe(820);
+    expect(resolveSidebarResizeMaxWidth(480)).toBe(SIDEBAR_RESIZE_MIN_WIDTH);
+  });
+});
diff --git a/frontend/src/utils/sidebarLayout.ts b/frontend/src/utils/sidebarLayout.ts
new file mode 100644
index 00000000..a7092e0b
--- /dev/null
+++ b/frontend/src/utils/sidebarLayout.ts
@@ -0,0 +1,27 @@
+export const DEFAULT_SIDEBAR_WIDTH = 330;
+export const SIDEBAR_RESIZE_MIN_WIDTH = 200;
+export const SIDEBAR_SIDER_MIN_WIDTH = 232;
+export const SIDEBAR_RESIZE_MAX_WIDTH = 960;
+export const SIDEBAR_MIN_WORKBENCH_WIDTH = 360;
+
+export const resolveSidebarResizeMaxWidth = (
+  viewportWidth: unknown,
+  minWidth = SIDEBAR_RESIZE_MIN_WIDTH,
+): number => {
+  const parsedViewportWidth = Number(viewportWidth);
+  if (!Number.isFinite(parsedViewportWidth) || parsedViewportWidth <= 0) {
+    return SIDEBAR_RESIZE_MAX_WIDTH;
+  }
+
+  const viewportLimitedWidth = Math.trunc(parsedViewportWidth) - SIDEBAR_MIN_WORKBENCH_WIDTH;
+  return Math.max(minWidth, Math.min(SIDEBAR_RESIZE_MAX_WIDTH, viewportLimitedWidth));
+};
+
+export const sanitizeSidebarWidth = (value: unknown): number => {
+  const parsed = Number(value);
+  if (!Number.isFinite(parsed)) return DEFAULT_SIDEBAR_WIDTH;
+  return Math.max(
+    SIDEBAR_RESIZE_MIN_WIDTH,
+    Math.min(SIDEBAR_RESIZE_MAX_WIDTH, Math.trunc(parsed)),
+  );
+};
diff --git a/frontend/src/v2-theme.css b/frontend/src/v2-theme.css
index ca416113..82d24c3e 100644
--- a/frontend/src/v2-theme.css
+++ b/frontend/src/v2-theme.css
@@ -1758,7 +1758,7 @@ body[data-ui-version="v2"] .gn-v2-sidebar-shell {
 
 body[data-ui-version="v2"] .gn-v2-app-sider {
   min-width: 232px !important;
-  max-width: 420px !important;
+  max-width: min(960px, calc(100vw - 360px)) !important;
 }
 
 body[data-ui-version="v2"] .gn-v2-sidebar-redesign {