[VS Code] 404 Unknown error after stopping a task, switching to GPT-5.6 SOL Ultra, and retrying

What version of the IDE extension are you using?

Codex - 26.825.51511

What subscription do you have?

pro

Which IDE are you using?

vscode

What platform is your computer?

Windows 11, x64 (build 26200.9168)

What issue are you seeing?

After stopping a running Codex task because I noticed that it was using a lower model/reasoning setting than I intended, I switched the model to GPT-5.6 SOL with High reasoning and retried the task.

After doing this, the conversation repeatedly enters:

Reconnecting 1/5
Reconnecting 2/5
...
Reconnecting 5/5

and then fails with:

unexpected status 404 Not Found: Unknown error, url: https://chatgpt.com/backend-api/codex/responses

Retrying the request in the same conversation produces the same reconnect sequence and the same 404 error, so I can no longer continue the task normally.

The issue appeared immediately after stopping the previous run, changing the model/reasoning setting, and retrying.

CF-Ray: [a355a47d584ba422-ICN]

What steps can reproduce the bug?

1. Open a repository in VS Code and open the Codex IDE extension.

2. Start a task using a lower model or reasoning setting than intended.

3. Stop/cancel the running task before it completes.

4. Change the model to GPT-5.6 SOL and set the reasoning level to High.

5. Retry the task in the same conversation/thread.

6. Codex** starts reconnecting repeatedly from Reconnecting 1/5 through Reconnecting 5/5.

7. After the final reconnect attempt, the request fails with:
   unexpected status 404 Not Found: Unknown error, url: https://chatgpt.com/backend-api/codex/responses

8. Retrying again in the same thread results in the same behavior.

What is the expected behavior?

After stopping a running task and changing the model, Codex should start a new request using the newly selected model and reasoning setting.

The existing conversation should remain usable without entering a repeated reconnect loop.

If the existing session cannot be reused after a model change, Codex should reset or recreate the session automatically, or display an actionable error message instead of retrying five times and returning an HTTP 404.

Additional information

No response

Reproduce the stop, model change, and retry sequence in the VS Code extension, then trace its reconnect handling for the /backend-api/codex/responses endpoint. Check how the existing conversation is reused after cancellation and model changes. Done means the retried task remains usable or produces an actionable error without the repeated five-attempt 404 loop.