The best outcome of bringing in a specialist is a team that can do more after the engagement than it could before.
Define the gap before the job title
A delayed roadmap might need another engineer. It might also need clearer architecture, stronger delivery practices, or a better-shaped backlog. Describe the work that is stuck and the outcome you want. Then define the experience that will help.
Choose an engagement that fits how you work
Staff augmentation brings specialists into your existing team and direction. A managed service delegates an agreed area of delivery to a provider. Neither is universally better. If you want day-to-day direction and close collaboration, an embedded specialist can be a natural fit.
Make onboarding real work
Access, domain context, a clear first task, and a named internal partner make a meaningful difference. Give a specialist enough information to make good decisions, including the constraints and trade-offs behind your current system.
Plan the handover at the start
Agree on what should remain with your organization: code, documentation, runbooks, design decisions, and operational skills. Review progress against those deliverables throughout the engagement. Knowledge transfer works best as a habit, not a final presentation.