[Windows] Markdown and DOCX previews fail while Review diff still works

What version of the Codex App are you using (From “About Codex” dialog)?

26.707.62119

What subscription do you have?

ChatGPT Plus

What platform is your computer?

Microsoft Windows NT 10.0.26200.0 x64

What issue are you seeing?

I am experiencing a file-preview problem in the Codex desktop app on Windows 11.

When I click a Markdown (.md) file created or referenced by Codex, a preview tab opens and the file breadcrumb/path is displayed, but the document content does not load. Codex shows the exact error message:

Could not open file

For example, the issue occurred when opening:

docs/superpowers/specs/2026-07-13-preview-hapus-video-sounding-design.md

The tab, breadcrumb, View source, and Open controls are visible, but the preview content remains blank.

Microsoft Word (.docx) documents also fail to load in the right-side preview panel. The exact message displayed is:

Couldn’t load this preview

The affected files still exist in the project and can be opened outside the Codex preview.

The Review diff viewer continues to work correctly. I can view files edited by Codex, added and removed lines, syntax-highlighted diffs, and the list of changed files. This suggests the problem affects the regular document/file preview renderer rather than the entire right-side panel.

What steps can reproduce the bug?

1. Open a local project in the Codex desktop app on Windows 11.
2. Ask Codex to create, edit, or reference a Markdown (.md) file.
3. Click the Markdown file link shown in the conversation.
4. Observe that the right-side preview tab opens.
5. Observe that the content does not load and Codex displays Could not open file.
6. Create or open a Microsoft Word (.docx) document from the same project.
7. Observe that its preview displays Couldn’t load this preview.
8. Open the Review panel for files edited by Codex.
9. Observe that the Review diff viewer still loads and works normally.

The issue is reproducible with regular local project files and is not specific to the Review diff viewer.

A minimal Markdown file that reproduces the issue:

# Preview test

This is a valid Markdown document.

What is the expected behavior?

Markdown files should render their formatted content in the right-side preview panel, and valid Word (.docx) documents should display through the built-in document previewer.

If a file cannot be rendered, Codex should fall back to a source/plain-text view when possible and provide a more specific diagnostic message explaining whether the failure is related to the file path, permissions, encoding, unsupported document features, file corruption, or the preview renderer.

Additional information

• Operating system: Windows 11, 64-bit
• Application: Codex desktop app
• Powered by: Codex & OWL
• Version: 26.707.62119
• Release date shown in About Codex: July 13, 2026
• Subscription: ChatGPT Plus
• Session ID: 019f59ac-7e12-7f12-8378-cda19db9a62c

The problem affects the regular file/document preview panel, while the Review panel for Codex edits continues to display line-by-line diffs correctly.