Codex Web App fails to attach a valid Markdown (.md) file to the prompt.

What issue are you seeing?

The Codex web app fails to attach a valid Markdown (.md) file to the prompt.

I can consistently reproduce the issue - with any .md file.

The file is not getting uploaded. There is no actionable error message shown in the UI.

The same behavior occurs with larger Markdown files as well.

<img width="854" height="276" alt="Image" src="https://github.com/user-attachments/assets/a6833b69-4293-47be-bcae-e47ca90dda73" />

What steps can reproduce the bug?

1. Open the Codex web app.
2. Start a new chat.
3. Create a Markdown file named do_nothing.md with the following contents:

Do nothing

(or just download the .md file attached)

1. Click the attachment button (or drag and drop the file into the prompt).
2. Observe that the file is not attached.

This reproduces consistently.

do_nothing.md

What is the expected behavior?

The Markdown file should upload successfully and appear as an attachment in the prompt so it can be used as context by Codex.

Additional information

• Platform: Codex Web App
• Subscription: ChatGPT Go
• Browser: Brave
• OS: macOS

The issue reproduces with both:

• a minimal one-line Markdown file (do_nothing.md)
• a larger Markdown specification document