diff --git a/packages/web-shell/client/components/panels/EnvironmentPanel.test.tsx b/packages/web-shell/client/components/panels/EnvironmentPanel.test.tsx
index 2d74dd95ddd..f4368a75d1c 100644
--- a/packages/web-shell/client/components/panels/EnvironmentPanel.test.tsx
+++ b/packages/web-shell/client/components/panels/EnvironmentPanel.test.tsx
@@ -3,7 +3,7 @@
 import type { DaemonSessionTaskStatus } from '@qwen-code/sdk/daemon';
 import { act, type ReactNode } from 'react';
 import { createRoot, type Root } from 'react-dom/client';
-import { afterEach, describe, expect, it, vi } from 'vitest';
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
 import { I18nProvider } from '../../i18n';
 import { EnvironmentPanel } from './EnvironmentPanel';
 import type { SourcesState } from './SourcesSection';
@@ -44,11 +44,17 @@ Object.assign(globalThis, { IS_REACT_ACT_ENVIRONMENT: true });
 let container: HTMLDivElement | null = null;
 let root: Root | null = null;
 
+beforeEach(() => {
+  // The add-source button is hidden by default; enable it for these tests.
+  window.history.replaceState({}, '', '/?addSource=1');
+});
+
 afterEach(() => {
   act(() => root?.unmount());
   container?.remove();
   container = null;
   root = null;
+  window.history.replaceState({}, '', '/');
 });
 
 function mount(
diff --git a/packages/web-shell/client/components/panels/SourcesSection.test.tsx b/packages/web-shell/client/components/panels/SourcesSection.test.tsx
new file mode 100644
index 00000000000..c7555b47129
--- /dev/null
+++ b/packages/web-shell/client/components/panels/SourcesSection.test.tsx
@@ -0,0 +1,62 @@
+// @vitest-environment jsdom
+
+import { act } from 'react';
+import { createRoot, type Root } from 'react-dom/client';
+import { afterEach, describe, expect, it, vi } from 'vitest';
+import { I18nProvider } from '../../i18n';
+import { SourcesSection, type SourcesState } from './SourcesSection';
+
+Object.assign(globalThis, { IS_REACT_ACT_ENVIRONMENT: true });
+
+let container: HTMLDivElement | null = null;
+let root: Root | null = null;
+
+afterEach(() => {
+  act(() => root?.unmount());
+  container?.remove();
+  container = null;
+  root = null;
+  window.history.replaceState({}, '', '/');
+});
+
+function supportedState(): SourcesState {
+  return {
+    supported: true,
+    sources: [],
+    owner: { isCurrent: () => true },
+    revision: 1,
+    hydrated: true,
+    loading: false,
+    error: null,
+    refresh: vi.fn(),
+    upsert: vi.fn(),
+    remove: vi.fn(),
+  };
+}
+
+function mount(): HTMLDivElement {
+  container = document.createElement('div');
+  document.body.appendChild(container);
+  root = createRoot(container);
+  act(() => {
+    root!.render(
+      <I18nProvider language="en">
+        <SourcesSection state={supportedState()} />
+      </I18nProvider>,
+    );
+  });
+  return container;
+}
+
+describe('SourcesSection add-source button', () => {
+  it('is hidden by default', () => {
+    const el = mount();
+    expect(el.querySelector('button[aria-label="Add source"]')).toBeNull();
+  });
+
+  it('appears when the addSource URL parameter is set', () => {
+    window.history.replaceState({}, '', '/?addSource=1');
+    const el = mount();
+    expect(el.querySelector('button[aria-label="Add source"]')).not.toBeNull();
+  });
+});
diff --git a/packages/web-shell/client/components/panels/SourcesSection.tsx b/packages/web-shell/client/components/panels/SourcesSection.tsx
index 173d25cedea..81393fac7c9 100644
--- a/packages/web-shell/client/components/panels/SourcesSection.tsx
+++ b/packages/web-shell/client/components/panels/SourcesSection.tsx
@@ -18,6 +18,13 @@ import styles from './EnvironmentPanel.module.css';
 
 export type SourcesState = ReturnType<typeof useSessionSources>;
 
+// Escape hatch: the add-source affordance is hidden by default; append
+// ?addSource=1 to the URL to bring it back.
+function isAddSourceEnabled(): boolean {
+  if (typeof window === 'undefined') return false;
+  return new URLSearchParams(window.location.search).get('addSource') === '1';
+}
+
 interface SourcesSectionProps {
   hidden?: boolean;
   state?: SourcesState;
@@ -97,7 +104,7 @@ export function SourcesSection({
           {t('sources.title')}{' '}
           <span className="text-muted-foreground">{entries.length}</span>
         </h3>
-        {state?.supported && (
+        {state?.supported && isAddSourceEnabled() && (
           <button
             type="button"
             className={styles.sectionAction}