- Return 404 Not Found when no orchestration with the given ID exists
- Return 200 OK for failed workflows (the HTTP operation succeeded;
the workflow outcome is conveyed via the response body)
- Rename 'status' to 'workflowStatus' in WorkflowRunResponse to avoid
inconsistency with AgentRunSuccessResponse which uses integer status
- Add optional 'error' field (omitted from JSON when null) to
WorkflowRunResponse for failed workflow details