Windows sandbox helper fails when patching an existing file

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

26.715.4045.0

What subscription do you have?

Plus

What platform is your computer?

Microsoft Windows NT 10.0.26200.0 x64

What issue are you seeing?

The Codex Windows app can create a new file, but modifying an existing file with
the normal patch tool fails immediately with windows sandbox: helper_unknown_error.

What steps can reproduce the bug?

Feedback ID: no-active-thread-019f74d1-1792-7a51-88bf-84d438e78a85

1. Open a disposable local folder outside Google Drive and outside Git.
2. Ask Codex to create test.txt using the normal patch tool.
3. File creation succeeds.
4. Ask Codex to modify the existing line in test.txt.
5. It immediately fails with windows sandbox: helper_unknown_error.

Codex was updated and Windows was fully restarted before repeating the test.
The failure still occurred.

What is the expected behavior?

Codex should modify the existing test.txt file and read back the updated contents without a sandbox/helper error.

Additional information

Actual behavior:

Creating test.txt with the normal patch tool succeeds, but modifying the existing
file immediately fails with:

windows sandbox: helper_unknown_error

I reproduced this in a disposable local folder outside Google Drive and outside
a Git repository. I updated Codex and fully restarted Windows before testing
again. File creation still succeeded, but modification still failed.

Reproduction:

1. Open a disposable local folder.
2. Ask Codex to create test.txt using the normal patch tool.
3. Ask Codex to change the existing line.
4. The sandbox helper error occurs immediately.

Feedback ID:
no-active-thread-019f74d1-1792-7a51-88bf-84d438e78a85