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@DataJpaTest + Postgres Testcontainer; 7 cases per Sara blocker 1: - addRelationship_stores_and_is_readable - addRelationship_throws_409_when_duplicate (unique_rel) - addRelationship_throws_409_when_circular_parent - deleteRelationship_throws_403_when_rel_belongs_to_different_person - deleteRelationship_succeeds_for_symmetric_type_from_either_side - setFamilyMember_true_makes_person_appear_in_network - delete_person_cascades_to_relationships Service now uses saveAndFlush so the unique_rel violation surfaces synchronously inside the @Transactional method (otherwise the DataIntegrityViolation fires at commit time, outside the try-catch). Unit-test mocks updated accordingly. Backend suite: 1406/1406 green. Refs #358. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>