How would you initialize an expensive shared object exactly once in a thread-safe way in .NET?

In production I would ask whether lazy creation is actually desirable. A required dependency may be better initialized and health-checked during startup so failure appears before traffic arrives, while an optional expensive feature may benefit from lazy loading. I would define timeout, cancellation, retry, refresh, and disposal ownership rather than hiding those policies in a property getter. If retries are allowed, exactly once is no longer the full contract; the design needs one active attempt, safe publication of success, and a controlled transition after failure. I would expose initialization duration and failure state because a first-request latency spike or permanently cached exception should not be mysterious.