Codex App create_thread reports failure after creating the task, causing duplicates

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

26.727.51351 (build 6119)

What subscription do you have?

Pro

What platform is your computer?

Darwin 25.5.0 arm64 arm

What issue are you seeing?

On macOS, the Codex App create_thread tool creates a task successfully but returns an error instead of the created thread ID.

Because the caller reasonably interprets the response as a failure and retries, duplicate tasks are created.

This occurred on five observed calls across two saved local Git projects. Subsequent list_threads calls confirmed that every supposedly failed creation had actually produced a usable task.

Observed errors:

Unknown projectId: <redacted>. Call list_projects to find available projects.

Something went wrong while running this tool.

Impact: the assistant reports that no task was created, retries the operation, and creates multiple active tasks with the same prompt.

What steps can reproduce the bug?

1. Open a Codex task and call list_projects.
2. Select a valid saved local Git project from the returned results.
3. Call create_thread with that project ID, environment type local, and a normal prompt.
4. Observe that create_thread returns either Unknown projectId or Something went wrong while running this tool.
5. Call list_threads.
6. Observe that the supposedly failed task was actually created and is running or idle normally.
7. Retry create_thread after the error.
8. Call list_threads again and observe an additional duplicate task.

Session ID: 019f5ea7-9c13-7112-8fbe-dd8ed80a63aa
Token limit usage: not provided
Context window usage: not provided

No code sample is required.

What is the expected behavior?

If task creation succeeds, create_thread should return the created threadId or clientThreadId.

If task creation fails, no task should be created.

The tool response and persisted task state must never disagree.

Additional information

Codex App: 26.727.51351 (build 6119)
macOS: 26.5.2 (build 25F84)

In one sequence, list_projects first returned a remote-style project ID that create_thread rejected. A subsequent list returned a local-style ID, but create_thread returned the generic error while still creating the task.

Five duplicate tasks were verified afterward and the extras were archived manually.

Related: #31119 describes a similar false-failure/duplicate-worker symptom on Windows, but that report involves missing handlers and systemError workers. This report is macOS-specific, uses different error responses, and the created tasks initialize normally.