[macOS] “Default app” does not open Markdown files in Obsidian

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

26.803.41515

What subscription do you have?

Pro

What platform is your computer?

Darwin 27.0.0 arm64 arm

What issue are you seeing?

In Codex Settings → General, Default file open destination is set to
Default app. macOS Finder has Obsidian configured as the default
application for .md files.

When I click a Markdown file link or reference inside Codex, the file does
not open in Obsidian. No other application opens and there is no visible
error message.

This may be a regression: with an earlier version of Codex, the same setup
appeared to open Markdown files in Obsidian correctly.

What steps can reproduce the bug?

1. Configure Obsidian as the macOS default application for .md files.
2. In Codex, open Settings → General.
3. Set Default file open destination to Default app.
4. Open a local project containing a Markdown file.
5. Create or edit a .md file in Codex.
6. Click the file link or reference shown in Codex.
7. Observe that Obsidian does not open.

What is the expected behavior?

Codex should ask macOS to open the Markdown file with its registered default
application, which is Obsidian.

Additional information

Control test

Double-clicking the exact same .md file in Finder successfully opens it in
Obsidian. Finder’s Get Info → Open with section shows:

• Obsidian.app (default)
• The association applies to all .md files

This indicates that the macOS file association and Obsidian are working
outside Codex.

Environment

• ChatGPT/Codex desktop app: 26.803.41515
• macOS: 27.0 Beta (26A5388g)
• Hardware: Apple Silicon M1
• Obsidian: [insert version]
• Codex setting: Default file open destination → Default app
• File type tested: .md
• Project type: Local Codex project

Additional information

I can provide:

• A screenshot showing Obsidian as the macOS default application for .md

files

• A screenshot of the Codex file-opening setting
• A screen recording reproducing the issue

Because this is occurring on macOS 27 beta, I cannot determine whether it is
a general Codex regression or a compatibility issue specific to that macOS
beta.