diff --git a/src/renderer/src/components/native-chat/NativeChatComposer.tsx b/src/renderer/src/components/native-chat/NativeChatComposer.tsx
index b11da6676f9..9081f6adf65 100644
--- a/src/renderer/src/components/native-chat/NativeChatComposer.tsx
+++ b/src/renderer/src/components/native-chat/NativeChatComposer.tsx
@@ -1,4 +1,4 @@
-import { forwardRef, useCallback, useImperativeHandle, useMemo, useRef, useState } from 'react'
+import { forwardRef, useCallback, useImperativeHandle, useMemo, useState } from 'react'
 import { useAppStore } from '../../store'
 import { sendRuntimePtyInput } from '@/runtime/runtime-terminal-inspection'
 import { getSettingsForAgentTabRuntimeOwner } from '@/lib/agent-paste-draft'
@@ -37,6 +37,7 @@ import type {
 import { dispatchNativeChatStructuredComposerText } from './native-chat-structured-composer-dispatch'
 import { useNativeChatPtyComposerSend } from './use-native-chat-pty-composer-send'
 import { useImeEnterGestureOwnership } from '@/lib/ime-composition-keyboard-event'
+import { useNativeChatComposerAppMenuSelection } from './use-native-chat-composer-app-menu-selection'
 
 export type {
   NativeChatComposerHandle,
@@ -97,8 +98,8 @@ const NativeChatComposerPane = forwardRef<NativeChatComposerHandle, NativeChatCo
     const [activeSuggestion, setActiveSuggestion] = useState(0)
     const [notice, setNotice] = useState<string | null>(null)
     const [dictationPressed, setDictationPressed] = useState(false)
-    const textareaRef = useRef<HTMLTextAreaElement>(null)
     const imeEnterGesture = useImeEnterGestureOwnership()
+    const { textareaRef } = useNativeChatComposerAppMenuSelection(imeEnterGesture.isComposing)
     const { cancelPendingSends, trackPendingSend } = useNativeChatSendLifecycle(
       terminalTabId,
       targetPtyId,
diff --git a/src/renderer/src/components/native-chat/use-native-chat-composer-app-menu-selection.test.tsx b/src/renderer/src/components/native-chat/use-native-chat-composer-app-menu-selection.test.tsx
new file mode 100644
index 00000000000..9fca062e058
--- /dev/null
+++ b/src/renderer/src/components/native-chat/use-native-chat-composer-app-menu-selection.test.tsx
@@ -0,0 +1,147 @@
+// @vitest-environment happy-dom
+
+import { act, cleanup, fireEvent, render } from '@testing-library/react'
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
+import {
+  APP_MENU_SELECTION_ACTION_EVENT,
+  type AppMenuSelectionAction
+} from '@/lib/app-menu-selection-actions'
+import { useAppMenuSelectionActions } from '@/hooks/useAppMenuSelectionActions'
+import { useNativeChatComposerAppMenuSelection } from './use-native-chat-composer-app-menu-selection'
+
+let appMenuListener: ((action: AppMenuSelectionAction) => void) | null = null
+const performNativeSelectionAction = vi.fn()
+
+function AppMenuBoundary(): null {
+  useAppMenuSelectionActions()
+  return null
+}
+
+function ComposerHarness(): React.JSX.Element {
+  const { textareaRef, isComposingRef } = useNativeChatComposerAppMenuSelection()
+  return (
+    <div>
+      <textarea
+        aria-label="Composer"
+        ref={textareaRef}
+        defaultValue={'first line\nsecond line'}
+        onCompositionStart={() => {
+          isComposingRef.current = true
+        }}
+        onCompositionEnd={() => {
+          isComposingRef.current = false
+        }}
+      />
+      <button type="button">Outside composer</button>
+    </div>
+  )
+}
+
+function emitAppMenuAction(action: AppMenuSelectionAction): void {
+  act(() => {
+    if (!appMenuListener) {
+      throw new Error('app menu listener is not registered')
+    }
+    appMenuListener(action)
+  })
+}
+
+function renderBoundaryAndComposer() {
+  const boundary = render(<AppMenuBoundary />)
+  const composer = render(<ComposerHarness />)
+  return { boundary, composer }
+}
+
+beforeEach(() => {
+  appMenuListener = null
+  performNativeSelectionAction.mockReset()
+  Object.defineProperty(window, 'api', {
+    configurable: true,
+    value: {
+      ui: {
+        onAppMenuSelectionAction: vi.fn((listener: typeof appMenuListener) => {
+          appMenuListener = listener
+          return () => {
+            appMenuListener = null
+          }
+        }),
+        performNativeSelectionAction
+      }
+    }
+  })
+})
+
+afterEach(() => {
+  cleanup()
+  vi.restoreAllMocks()
+})
+
+describe('native chat app-menu selection ownership', () => {
+  it('selects the focused multiline composer through the app-menu boundary', () => {
+    const { composer } = renderBoundaryAndComposer()
+    const textarea = composer.getByRole('textbox', { name: 'Composer' }) as HTMLTextAreaElement
+    textarea.focus()
+    textarea.setSelectionRange(4, 4)
+
+    emitAppMenuAction('select-all')
+
+    expect(textarea.selectionStart).toBe(0)
+    expect(textarea.selectionEnd).toBe(textarea.value.length)
+    expect(performNativeSelectionAction).not.toHaveBeenCalled()
+  })
+
+  it('preserves global fallback when focus is outside the composer', () => {
+    const { composer } = renderBoundaryAndComposer()
+    const textarea = composer.getByRole('textbox', { name: 'Composer' }) as HTMLTextAreaElement
+    textarea.setSelectionRange(4, 4)
+    composer.getByRole('button', { name: 'Outside composer' }).focus()
+
+    emitAppMenuAction('select-all')
+
+    expect(textarea.selectionStart).toBe(4)
+    expect(textarea.selectionEnd).toBe(4)
+    expect(performNativeSelectionAction).toHaveBeenCalledOnce()
+    expect(performNativeSelectionAction).toHaveBeenCalledWith('select-all')
+  })
+
+  it('leaves non-select-all actions unclaimed', () => {
+    const { composer } = renderBoundaryAndComposer()
+    const textarea = composer.getByRole('textbox', { name: 'Composer' }) as HTMLTextAreaElement
+    textarea.focus()
+
+    emitAppMenuAction('copy')
+
+    expect(performNativeSelectionAction).toHaveBeenCalledOnce()
+    expect(performNativeSelectionAction).toHaveBeenCalledWith('copy')
+  })
+
+  it('claims select-all during active IME composition without selecting or falling back', () => {
+    const { composer } = renderBoundaryAndComposer()
+    const textarea = composer.getByRole('textbox', { name: 'Composer' }) as HTMLTextAreaElement
+    textarea.focus()
+    textarea.setSelectionRange(4, 4)
+    fireEvent.compositionStart(textarea)
+
+    emitAppMenuAction('select-all')
+
+    expect(textarea.selectionStart).toBe(4)
+    expect(textarea.selectionEnd).toBe(4)
+    expect(performNativeSelectionAction).not.toHaveBeenCalled()
+  })
+
+  it('removes composer ownership on cleanup', () => {
+    const addEventListener = vi.spyOn(window, 'addEventListener')
+    const removeEventListener = vi.spyOn(window, 'removeEventListener')
+    const { composer } = renderBoundaryAndComposer()
+    const listener = addEventListener.mock.calls.find(
+      ([eventName]) => eventName === APP_MENU_SELECTION_ACTION_EVENT
+    )?.[1]
+
+    composer.unmount()
+
+    expect(listener).toBeDefined()
+    expect(removeEventListener).toHaveBeenCalledWith(APP_MENU_SELECTION_ACTION_EVENT, listener)
+    emitAppMenuAction('select-all')
+    expect(performNativeSelectionAction).toHaveBeenCalledWith('select-all')
+  })
+})
diff --git a/src/renderer/src/components/native-chat/use-native-chat-composer-app-menu-selection.ts b/src/renderer/src/components/native-chat/use-native-chat-composer-app-menu-selection.ts
new file mode 100644
index 00000000000..d41117e42ac
--- /dev/null
+++ b/src/renderer/src/components/native-chat/use-native-chat-composer-app-menu-selection.ts
@@ -0,0 +1,38 @@
+import { useCallback, useEffect, useRef } from 'react'
+import {
+  APP_MENU_SELECTION_ACTION_EVENT,
+  type AppMenuSelectionAction
+} from '@/lib/app-menu-selection-actions'
+
+export function useNativeChatComposerAppMenuSelection(
+  isComposingOverride?: () => boolean
+) {
+  const textareaRef = useRef<HTMLTextAreaElement>(null)
+  const isComposingRef = useRef(false)
+  const isComposing = useCallback(
+    () => isComposingOverride?.() ?? isComposingRef.current,
+    [isComposingOverride]
+  )
+
+  useEffect(() => {
+    const onSelectionAction = (event: Event): void => {
+      const textarea = textareaRef.current
+      if (
+        (event as CustomEvent<AppMenuSelectionAction>).detail !== 'select-all' ||
+        !textarea ||
+        document.activeElement !== textarea
+      ) {
+        return
+      }
+      event.preventDefault()
+      if (!isComposing()) {
+        textarea.select()
+      }
+    }
+
+    window.addEventListener(APP_MENU_SELECTION_ACTION_EVENT, onSelectionAction)
+    return () => window.removeEventListener(APP_MENU_SELECTION_ACTION_EVENT, onSelectionAction)
+  }, [isComposing, textareaRef])
+
+  return { textareaRef, isComposingRef, isComposing }
+}
diff --git a/src/renderer/src/lib/editable-target.test.ts b/src/renderer/src/lib/editable-target.test.ts
new file mode 100644
index 00000000000..c1cc71f2361
--- /dev/null
+++ b/src/renderer/src/lib/editable-target.test.ts
@@ -0,0 +1,45 @@
+// @vitest-environment happy-dom
+
+import { afterEach, describe, expect, it } from 'vitest'
+import { isSelectAllShortcut } from './editable-target'
+
+const originalUserAgent = navigator.userAgent
+
+function setPlatformUserAgent(userAgent: string): void {
+  Object.defineProperty(navigator, 'userAgent', { configurable: true, value: userAgent })
+}
+
+function keyEvent(overrides: Partial<Parameters<typeof isSelectAllShortcut>[0]> = {}) {
+  return {
+    altKey: false,
+    ctrlKey: false,
+    key: 'a',
+    metaKey: false,
+    shiftKey: false,
+    ...overrides
+  }
+}
+
+afterEach(() => setPlatformUserAgent(originalUserAgent))
+
+describe('isSelectAllShortcut', () => {
+  it.each([
+    ['macOS Cmd+A', 'Macintosh', { metaKey: true }],
+    ['Linux Ctrl+A', 'Linux x86_64', { ctrlKey: true }],
+    ['Windows Ctrl+A', 'Windows NT 10.0', { ctrlKey: true }]
+  ])('recognizes %s', (_label, userAgent, modifiers) => {
+    setPlatformUserAgent(userAgent)
+
+    expect(isSelectAllShortcut(keyEvent(modifiers))).toBe(true)
+  })
+
+  it.each([
+    ['macOS Ctrl+A', 'Macintosh', { ctrlKey: true }],
+    ['Linux Cmd+A', 'Linux x86_64', { metaKey: true }],
+    ['Windows Cmd+A', 'Windows NT 10.0', { metaKey: true }]
+  ])('rejects wrong-modifier %s', (_label, userAgent, modifiers) => {
+    setPlatformUserAgent(userAgent)
+
+    expect(isSelectAllShortcut(keyEvent(modifiers))).toBe(false)
+  })
+})