[Windows] “Open in folder” falls back to C:\ for mapped-drive/UNC project files

Summary

In the Windows Codex desktop app, Open in folder fails for a file in a project saved using a mapped network drive. The file preview works, but File Explorer opens at C:\ instead of the containing folder.

Environment

• Codex Windows app package: 26.810.4967.0
• Windows-native agent
• Local non-Git project
• Project saved as X:\workspace, where X: maps to a UNC network share

Steps to reproduce

1. Open a local project saved through a mapped network drive.
2. Open a generated or edited file in Codex’s file preview.
3. Choose Open → Open in folder.

Actual behavior

File Explorer opens at C:\ and does not navigate to or select the file.

Expected behavior

File Explorer opens the file’s containing folder and selects the file.

Diagnostics

• The saved project path remains the mapped-drive path.
• Both the mapped-drive and UNC forms exist and are accessible.
• Running Explorer directly with the mapped-drive file path works.
• The preview displays the file successfully.
• Based on these observations, Codex may be normalizing the preview path to UNC before invoking Explorer; this is an inference rather than a confirmed root cause.

Privacy note

The affected project contains confidential enterprise data, so no session transcript, screenshot, identifying file path, or logs are attached. A sanitized reproduction can be provided if requested.

Start at the Windows desktop app's file preview flow and the Open → Open in folder entry point, then reproduce with a mapped-drive path and its UNC form. Trace the path passed to File Explorer; done means Explorer opens the containing folder and selects the file instead of falling back to C:.