diff --git a/apps/desktop/src/app/chat/right-rail/preview-file.test.tsx b/apps/desktop/src/app/chat/right-rail/preview-file.test.tsx
index 8436240460..01564253c3 100644
--- a/apps/desktop/src/app/chat/right-rail/preview-file.test.tsx
+++ b/apps/desktop/src/app/chat/right-rail/preview-file.test.tsx
@@ -1,7 +1,11 @@
-import { cleanup, render, screen } from '@testing-library/react'
-import { afterEach, describe, expect, it } from 'vitest'
+import { cleanup, fireEvent, render, screen } from '@testing-library/react'
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
 
-import { MarkdownPreview } from './preview-file'
+const { openFileWithSystemApp } = vi.hoisted(() => ({ openFileWithSystemApp: vi.fn() }))
+
+vi.mock('@/lib/office-files', () => ({ openFileWithSystemApp }))
+
+import { LocalFilePreview, MarkdownPreview } from './preview-file'
 
 // Behavior tests for the .md file preview renderer: input markdown goes
 // through normalizeFilePreviewMath -> Streamdown (+ KaTeX math plugin) and must
@@ -51,3 +55,50 @@ describe('MarkdownPreview', () => {
     expect(anchor?.getAttribute('rel')).toBe('noopener noreferrer')
   })
 })
+
+const binaryTarget = {
+  binary: true,
+  byteSize: 8_000,
+  kind: 'file' as const,
+  label: 'report.docx',
+  language: 'text',
+  large: false,
+  path: '/w/report.docx',
+  previewKind: 'binary' as const,
+  source: '/w/report.docx',
+  url: 'file:///w/report.docx'
+}
+
+describe('LocalFilePreview binary refusal', () => {
+  beforeEach(() => {
+    openFileWithSystemApp.mockReset().mockResolvedValue(true)
+  })
+
+  afterEach(() => {
+    cleanup()
+  })
+
+  it('makes the system app the primary action for binary files', () => {
+    render(<LocalFilePreview reloadKey={0} target={binaryTarget} />)
+
+    const primary = screen.getByRole('button', { name: 'Open with system app' })
+
+    expect(primary).not.toBeNull()
+    expect(screen.getByRole('button', { name: 'Preview anyway' })).not.toBeNull()
+
+    fireEvent.click(primary)
+    expect(openFileWithSystemApp).toHaveBeenCalledWith('/w/report.docx')
+  })
+
+  it('keeps Preview anyway primary for merely large text files', () => {
+    render(
+      <LocalFilePreview
+        reloadKey={0}
+        target={{ ...binaryTarget, binary: false, large: true, label: 'huge.log', path: '/w/huge.log' }}
+      />
+    )
+
+    expect(screen.getByRole('button', { name: 'Preview anyway' })).not.toBeNull()
+    expect(screen.queryByRole('button', { name: 'Open with system app' })).toBeNull()
+  })
+})
diff --git a/apps/desktop/src/app/chat/right-rail/preview-file.tsx b/apps/desktop/src/app/chat/right-rail/preview-file.tsx
index a16d64f280..198935ad61 100644
--- a/apps/desktop/src/app/chat/right-rail/preview-file.tsx
+++ b/apps/desktop/src/app/chat/right-rail/preview-file.tsx
@@ -34,6 +34,7 @@ import { createMemoizedMathPlugin } from '@/lib/katex-memo'
 import { isComposerChord } from '@/lib/keybinds/chords'
 import { shikiLanguageForFilename } from '@/lib/markdown-code'
 import { normalizeFilePreviewMath } from '@/lib/markdown-preprocess'
+import { openFileWithSystemApp } from '@/lib/office-files'
 import { cn } from '@/lib/utils'
 import type { PreviewTarget } from '@/store/preview'
 import { setPreviewDirty } from '@/store/preview-edit'
@@ -1034,11 +1035,19 @@ export function LocalFilePreview({ reloadKey, target }: { reloadKey: number; tar
   ) {
     const binary = target.binary || state.binary
     const size = target.byteSize || state.byteSize
+    const previewAnyway = () => setForcePreview(true)
 
     return (
       <PreviewEmptyState
         body={binary ? t.preview.binaryBody(target.label) : t.preview.largeBody(target.label, formatBytes(size))}
-        primaryAction={{ label: t.preview.previewAnyway, onClick: () => setForcePreview(true) }}
+        // Binary files can't render as text — the system default app is the
+        // useful way out; "Preview anyway" stays as the secondary escape hatch.
+        primaryAction={
+          binary
+            ? { label: t.preview.openWithSystemApp, onClick: () => void openFileWithSystemApp(filePath) }
+            : { label: t.preview.previewAnyway, onClick: previewAnyway }
+        }
+        secondaryAction={binary ? { label: t.preview.previewAnyway, onClick: previewAnyway } : undefined}
         title={binary ? t.preview.binaryTitle : t.preview.largeTitle}
         tone="warning"
       />