How does Spring handle circular dependencies, and why is a constructor cycle a design smell rather than something to patch with @Lazy?

Spring can resolve a setter/field-injection cycle using its three-level singleton cache that exposes early bean references, but a pure constructor-injection cycle can't be satisfied and the context fails to start with BeanCurrentlyInCreationException.

You can break it with @Lazy, setter injection, or an ObjectProvider, but those just hide that two beans are mutually responsible for each other. The senior move is to refactor: extract the shared logic into a third collaborator or publish an event, because a cycle usually signals a missing abstraction or a layering violation.