[Projects][Sources] Successful source uploads report failure and create duplicates on retry

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

26.818.21641

What subscription do you have?

Plus

What platform is your computer?

Microsoft Windows NT 10.0.26200.0 x64

What issue are you seeing?

When adding files as sources to an existing ChatGPT Project, the upload can complete successfully while ChatGPT reports that it failed.

In the ChatGPT desktop app, I repeatedly received:

Could not add sources
Library file is no longer available for project attachment

However, after reopening Project settings, the supposedly failed files were listed under Available sources and were fully readable by Project chats when instructed to use only Project sources.

I reproduced this with:

Test01.txt

LibraryTest02.txt

LibraryTest03.txt

I also reproduced the same false-negative behaviour in the ChatGPT web app. There, uploading a real .docx Project source displayed:

Unknown error occurred

Because the UI reported failure, I retried the upload. Both attempts had actually succeeded, which created duplicate Project sources.

The core problem is:

Project source uploads can succeed while ChatGPT reports failure, causing duplicate source attachments when users retry.

<img width="855" height="190" alt="Image" src="https://github.com/user-attachments/assets/75f840c2-ca61-467d-babc-4cb52fedd4aa" />

<img width="1628" height="1074" alt="Image" src="https://github.com/user-attachments/assets/353f7a37-2d3e-4adb-97d8-52de331d9552" />

What steps can reproduce the bug?

Feedback ID: no-active-thread-01a0206c-b459-7d31-9e3f-bb7c7ef67d75

What is the expected behavior?

If a Project source is added successfully, ChatGPT should report success and show the new source.

If the source genuinely fails to upload, ChatGPT should report failure and the source should not be added.

The UI should never report failure after a successful source attachment, because this encourages the user to retry and can create duplicate Project sources.

Additional information

Reproduction steps (GitHub reproduction field is locked)

Desktop app

Open an existing Cloud Project.

Open Project settings.

Under Available sources, click Add.

Select a file using Windows File Explorer.

Observe the error:
“Could not add sources — Library file is no longer available for project attachment.”

Close and reopen Project settings.

Observe that the file is actually listed under Available sources.

In a Project chat, ask ChatGPT to use only the Project's Available sources and read that file.

Observe that the supposedly failed file is accessible and readable.

This was reproduced with multiple .txt files.

Web app

Open the same Project in ChatGPT web.

Open the Sources tab.

Click Add sources and upload a .docx file.

Observe:
“Unknown error occurred.”

Retry the upload because the UI indicates that the first attempt failed.

Check the Project Sources list.

Observe that both attempts actually succeeded and duplicate copies of the source have been created.

The desktop and web interfaces show different error messages for the same general false-negative behaviour:

Desktop app: “Library file is no longer available for project attachment.”

Web app: “Unknown error occurred.”

In testing, Project sources remained fully readable despite the reported errors.

Project sources also appear to persist independently of File Library entries. For example, a test file remained attached and readable as a Project source after its File Library copy had been deleted.

The desktop app currently uses a newer Project/file-management interface than the web app, so the exact reproduction path differs between them.

The practical impact is that users cannot trust the reported upload result and may unintentionally create duplicate Project sources by retrying successful uploads.