Codex Web: first message fails with “Unable to determine project root for task” despite runnable cloud environment #49497

What issue are you seeing?

On September 30, 2026, submitting the first message in Codex Web fails after selecting a published saved cloud environment.

The test prompt is "hi". The UI displays:

• "Error submitting message"
• "Unable to determine project root for task"

The page remains on the "What should we build?" composer.

What steps can reproduce the bug?

1. Open Codex Web in a browser on Windows.
2. Select the intended published cloud environment.
3. Enter "hi" as the first message and submit.
4. Observe the errors above.
5. Hard-refresh with Ctrl+Shift+R, reselect the environment, and retry; the same failure occurs.

What is the expected behavior?

The message should submit and start a task using the selected environment. If additional configuration is required, the error should identify what needs to be changed.

Additional information

• Observed on September 30, 2026, around 05:53–05:57 UTC.
• Browser name/version and exact Windows version have not been recorded.
• A separate assistant-created diagnostic task successfully launched using the same published saved environment.
• Read-only diagnostics confirmed a valid repository checkout, HEAD, and root tree.
• The Install and Start instructions change into the intended repository directory.
• No repository code or environment configuration was changed during diagnosis.
• The cause of the difference between these launch paths is unknown.
• Related: [Windows Desktop] Failed Cloud chat creation leaves the conversation stuck with no way back to Local #38325 reports the same error during a Windows Desktop Local-to-Cloud handoff. This report concerns the first message in a new web chat; whether the cause is shared is unknown.

Repository names, environment/task IDs, settings screenshots, credentials, and configuration values are intentionally omitted.