Clarification of responsibility areas: state machine, Transactional Outbox, optimistic locking.

State Machine — is a model that describes a system through a set of states and transitions between them. In the context of business logic, it helps explicitly manage entity states and control permissible transitions, reducing the likelihood of errors and simplifying maintenance.

Transactional Outbox — is a pattern for ensuring reliable message delivery in distributed systems. When a state change occurs in the database, a record is simultaneously saved in the "outbox" table as part of the transaction. A separate process reads these records and sends messages to the queue, guaranteeing that changes and messages are synchronized.

Optimistic Locking — is a mechanism to prevent conflicts during concurrent data updates without explicit locking. It is usually implemented through a version field (e.g., version or updated_at). When saving, it checks that the version has not changed since it was read; if it has, the operation is rolled back and retried.

Together, these concepts help:

• State Machine — control transition logic and states.
• Transactional Outbox — ensure atomicity of changes and events for integration with other services.
• Optimistic Locking — avoid conflicts during concurrent updates without reducing performance.