diff --git a/apps/desktop/src/app/chat/composer/attachments.test.tsx b/apps/desktop/src/app/chat/composer/attachments.test.tsx
index 52e8f6bf98e8..b405b011d62e 100644
--- a/apps/desktop/src/app/chat/composer/attachments.test.tsx
+++ b/apps/desktop/src/app/chat/composer/attachments.test.tsx
@@ -1,11 +1,14 @@
-import { act, cleanup, render, screen } from '@testing-library/react'
+import { act, cleanup, fireEvent, render, screen } from '@testing-library/react'
 import { afterEach, describe, expect, it } from 'vitest'
 
 import { I18nProvider } from '@/i18n/context'
 import type { ComposerAttachment } from '@/store/composer'
+import { $previewTabs } from '@/store/preview'
 
 import { AttachmentList } from './attachments'
 
+const DATA_URL = 'data:image/png;base64,iVBORw0KGgoAAAANS'
+
 function makeAttachment(id: string, label = 'test.pdf'): ComposerAttachment {
   return { id, kind: 'file', label }
 }
@@ -66,4 +69,43 @@ describe('AttachmentList', () => {
 
     expect(screen.getByText('valid.txt')).toBeDefined()
   })
+
+  it('opens an attached image in the lightbox, not the preview rail', async () => {
+    $previewTabs.set([])
+
+    const image: ComposerAttachment = {
+      id: 'img',
+      kind: 'image',
+      label: 'shot.png',
+      path: '/tmp/shot.png',
+      previewUrl: DATA_URL
+    }
+
+    await renderWithI18n(<AttachmentList attachments={[image]} />)
+
+    await act(async () => {
+      fireEvent.click(screen.getByRole('button', { name: /shot\.png/ }))
+    })
+
+    // The lightbox renders the full-size image in a dialog; the rail stays empty.
+    const lightbox = await screen.findByRole('dialog')
+
+    expect(lightbox.querySelector<HTMLImageElement>('img')?.src).toBe(DATA_URL)
+    expect($previewTabs.get()).toHaveLength(0)
+  })
+
+  it('still routes a non-image attachment to the preview rail', async () => {
+    $previewTabs.set([])
+
+    const file: ComposerAttachment = { id: 'doc', kind: 'file', label: 'notes.md', path: '/tmp/notes.md' }
+
+    await renderWithI18n(<AttachmentList attachments={[file]} />)
+
+    await act(async () => {
+      fireEvent.click(screen.getByRole('button', { name: /notes\.md/ }))
+    })
+
+    expect(screen.queryByRole('dialog')).toBeNull()
+    expect($previewTabs.get().map(tab => tab.target.path)).toEqual(['/tmp/notes.md'])
+  })
 })