Codex App sends Z:\AREA_01 to the model as Z:\AREA\_01 while UI displays it correctly

What version of the Codex App are you using?

26.825.4187.0

What subscription do you have?

Not relevant to this client-side text serialization issue.

What platform is your computer?

Microsoft Windows NT 10.0.26200.0 x64

What issue are you seeing?

The Codex desktop app displays a Windows path correctly in the sent user-message bubble, but the text delivered to the model contains an extra backslash before the underscore.

The user sent and the UI displayed:

Z:\AREA_01

The model-visible user message was instead:

Z:\AREA\_01

This is not only a visual Markdown-rendering issue. The message content reaching the model was changed. As a result, the agent initially ran a read-only existence check against the nonexistent path Z:\AREA\_01 and reported it missing. A later directory scan found the actual existing path Z:\AREA_01.

The inserted Markdown escape character becomes a real path separator in a Windows path. This can misdirect file operations; in this case, fail-safe existence checks prevented any deletion or installation at the wrong location.

What steps can reproduce the bug?

1. Open a Codex desktop task on Windows.
2. Type a normal sentence containing the unformatted path Z:\AREA_01 (the reproduced prompt also contained Chinese text around the path).
3. Send the message.
4. Observe that the sent-message bubble still displays Z:\AREA_01.
5. Ask the model to repeat the exact path it received, or inspect the model-visible conversation input.
6. Observe that the model received Z:\AREA\_01.
7. A filesystem existence check confirms that Z:\AREA_01 exists while Z:\AREA\_01 does not.

What is the expected behavior?

User message text must be delivered to the model byte-for-byte for path-like content. The model should receive Z:\AREA_01, exactly as displayed in the sent-message bubble.

Additional information

This appears related to #32638, but the behavior is materially different. #32638 described underscores being interpreted as emphasis in the composer. Here the UI displays the path correctly after sending, while the serialized model input silently gains a backslash.

Likely boundary: rich-text/Markdown serialization adds an escape before _, and that escape is not removed before constructing the model input.

Current workarounds: wrap paths in inline code or use forward slashes such as Z:/AREA_01.

A screenshot is available showing the sent user-message bubble with the correct path and the assistant's model-side view with the extra backslash.

Start by reproducing the Windows path case and tracing the rich-text/Markdown serialization boundary into model input construction. Compare the text displayed in the sent-message bubble with the exact text delivered to the model; done means an unformatted path such as Z:\AREA_01 arrives unchanged, while existing inline-code and forward-slash workarounds remain unaffected.