openai/codex · error · anyhow::Error

reserved thread ID cannot be used when resuming a thread

Error message

reserved thread ID cannot be used when resuming a thread

What it means

Error "reserved thread ID cannot be used when resuming a thread" thrown in openai/codex.

Source

Thrown at codex-rs/core/src/session/session.rs:753

            Some(ThreadSource::Subagent | ThreadSource::GuardianReview)
        );
        if let InitialHistory::Forked(items) = &mut initial_history {
            Self::assign_missing_rollout_response_item_ids(items);
        }
        let multi_agent_version = multi_agent_version.map(OnceLock::from).unwrap_or_default();
        let initial_multi_agent_version = multi_agent_version.get().copied();

        let thread_id = match (&initial_history, reserved_thread_id) {
            (
                InitialHistory::New | InitialHistory::Cleared | InitialHistory::Forked(_),
                Some(thread_id),
            ) => thread_id,
            (InitialHistory::New | InitialHistory::Cleared | InitialHistory::Forked(_), None) => {
                agent_control.generate_thread_id()
            }
            (InitialHistory::Resumed(resumed_history), None) => resumed_history.conversation_id,
            (InitialHistory::Resumed(_), Some(_)) => {
                return Err(anyhow::anyhow!(
                    "reserved thread ID cannot be used when resuming a thread"
                ));
            }
        };
        let resumed_session_id = match &initial_history {
            InitialHistory::Resumed(resumed) => {
                resumed.history.iter().find_map(|item| match item {
                    RolloutItem::SessionMeta(meta_line) => Some(meta_line.meta.session_id),
                    _ => None,
                })
            }
            InitialHistory::New | InitialHistory::Cleared | InitialHistory::Forked(_) => None,
        };
        // Legacy subagent rollouts synthesize session_id from their own thread id.
        let resumed_session_id = resumed_session_id.filter(|session_id| {
            !session_configuration.session_source.is_non_root_agent()
                || *session_id != SessionId::from(thread_id)
        });

View on GitHub (pinned to 339751715c)

Solutions

1. Resume with a valid, non-reserved thread ID.

When it happens

Trigger: Thrown at codex-rs/core/src/session/session.rs:753 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of openai/codex@339751715c (2026-08-25). Data as JSON: /api/errors/003856c7463b2072. Report an issue: GitHub.