The operating model and Scope of Work for our service partner, covering geographic coverage, responsibilities, response times and SLAs, staffing, escalation paths, warranty pre-approval rules, spares, reporting, recovery of costs when the partner causes damage, and the scorecard you run it on, plus a qualified second partner behind it. It will not work for someone who hides behind service partners, passes tickets between customers and partners without making the call, routes every difficult issue directly to Engineering, measures success by closing tickets instead of restoring operation, or waits for perfect tooling before establishing ownership.