Without the annotation, Hibernate closes its sub-transaction after
eventRepository.findAll() returns, leaving TimelineEvent entities
detached. Accessing ev.getPersons() or doc.getReceivers() on those
detached entities throws LazyInitializationException in production
(constitution §1.6). @DataJpaTest and @Transactional test classes
masked the bug by keeping an outer session alive.
Fixes: @felix / @markus review blockers on PR #826
Refs #777
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>