Hmbown/CodeWhale · error

Cannot continue agent

Error message

Cannot continue agent {agent_id}: status is {} and the child cannot resume

What it means

Thrown by the continue-agent flow's catch-all arm when the child's status is one that can never be resumed: Failed, Cancelled, BudgetExhausted, or any other non-resumable state. Only Running (live delivery), Interrupted, and Completed statuses continue; everything else fails closed.

Solutions

1. Check the child's status first and only call continue for Interrupted/Completed/Running children.
2. For Failed or Cancelled children, spawn a new child with the original task plus any partial output.
3. For BudgetExhausted, increase the budget and spawn a fresh child (its budget is spent, not resumable).
4. Inspect the status detail via `subagent_status_name` to understand which terminal state blocked the resume.

Example fix

// before
let outcome = registry.continue_agent(&handle, &agent_ref, text, runtime)?;
// after
match registry.status_of(&agent_ref) {
    SubAgentStatus::Running | SubAgentStatus::Interrupted(_) | SubAgentStatus::Completed => {
        registry.continue_agent(&handle, &agent_ref, text, runtime)?
    }
    other => {
        let new_ref = registry.spawn_child_with_context(&original_task)?;
        registry.user_follow_up(&new_ref, text)?
    }
}

match registry.status_of(agent_ref) {
    SubAgentStatus::Running | SubAgentStatus::Interrupted(_) | SubAgentStatus::Completed => {},
    other => anyhow::bail!("agent is {:?}; cannot be continued, spawn a new child", other),
}

fn is_continueable(status: &SubAgentStatus) -> bool {
    matches!(status, SubAgentStatus::Running | SubAgentStatus::Interrupted(_) | SubAgentStatus::Completed)
}

match registry.continue_agent(&handle, agent_ref, text, runtime) {
    Err(e) if e.to_string().contains("cannot resume") => {
        let new_ref = registry.spawn_child_with_context(&original_task)?;
        registry.user_follow_up(&new_ref, text)?
    }
    r => r?,
}

When it happens

Trigger: Calling `continue_agent` on a child that failed, was cancelled, exhausted its budget, or is otherwise in a terminal non-resumable status (the `other =>` match arm).

Common situations: User hits 'continue' in the UI on a failed child; a retry script blindly continues agents regardless of status; a budget-exhausted child is continued without raising the budget; status changed to Failed between the check and the continue call.

Understand the failure class

Background: "Invalid state transition" errors: "status must be X, actually Y", "already rejected/charging/uninstalled", "cannot ... while running" — what they mean when a library rejects your call — this error's family across 31 libraries.

Related errors

• Cannot follow up agent
• Cannot resume agent : status is ( )
• Agent continuation target is no longer retained
• Agent continuation target is outside the active session
• Agent not found

AI-assisted analysis of Hmbown/CodeWhale@73e0f67d83 (2026-09-22). Data as JSON: /api/errors/4208e5f4943ab919. Report an issue: GitHub.

Appendix: source

Thrown at crates/tui/src/tools/subagent/mod.rs:6137

                    ));
                };
                let resumed = self.resume_from_checkpoint_with_policy(
                    manager_handle,
                    runtime,
                    &agent_id,
                    text,
                    ResumePolicy::InterruptedOrCompleted,
                )?;
                let target = resumed.agent_id.clone();
                Ok(UserFollowUpOutcome {
                    agent_id,
                    delivered: true,
                    resumed: true,
                    note: format!("continued from checkpoint as {target}"),
                    target_agent_id: target,
                })
            }
            other => Err(anyhow!(
                "Cannot continue agent {agent_id}: status is {} and the child cannot resume",
                subagent_status_name(&other)
            )),
        }
    }

    pub(crate) fn continue_child_from_user_for_session(
        &mut self,
        active_session_id: &str,
        manager_handle: SharedSubAgentManager,
        runtime: Option<SubAgentRuntime>,
        agent_ref: &str,
        text: &str,
    ) -> Result<UserFollowUpOutcome> {
        let agent_id = self.resolve_agent_ref_for_session(active_session_id, agent_ref)?;
        self.continue_child_from_user(manager_handle, runtime, &agent_id, text)
    }

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