Transaction boundaries as an architectural decision: where a transaction starts and ends, what isolation level actually buys, how propagation and rollback rules behave in practice, the costs of spanning a network call or a user's thinking time, and how to handle effects outside its atomic scope. Use when a use case writes twice and nobody can say whether it is atomic, when @Transactional sits on a repository or a controller, when a transaction stays open across an HTTP call or a message publish, when a rollback did not happen because the exception was checked or the call was self-invoked, when isolation is being raised to fix a race, when a read-only flag is added without…
