feat(person): enforce person-delete integrity at the DB layer (V71) (#684)

Add ON DELETE behaviour to the two V1 FKs into persons (documents.sender_id
-> SET NULL, document_receivers.person_id -> CASCADE) and a real FK with
ON DELETE CASCADE on the transcription_block_mentioned_persons soft reference,
cleaning up pre-existing orphan mention rows first. The cascade stays strictly
at the join/reference layer and never reaches documents rows.

Proven by new Postgres-backed PersonRepositoryTest cascade tests (AC-1/2/3/8
plus the cascade-boundary document-survival guard). Rewrites the now-stale
V56 'no FK' comment.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/src/main/resources/db/migration/V56__add_transcription_block_mentioned_persons.sql

@@ -8,12 +8,13 @@
 -- all blocks mentioning person X" query on the person detail page joins on
 -- the indexed person_id column — equally fast as JSONB GIN containment, no
 -- new dependency. document_comments.comment_mentions stays as a many-to-many
--- to AppUser; the divergence is intentional: Person mentions need lazy
--- degradation when a person is deleted (no FK), while user mentions don't.
+-- to AppUser; the divergence is intentional.
 --
--- No FK on person_id: when a Person is deleted we want @Auguste Raddatz to
--- remain visible as plain unlinked text inside the transcription rather than
--- vanishing or cascade-deleting the block.
+-- person_id FK: added in V71 with ON DELETE CASCADE (this column was originally
+-- created without a FK — that decision was reversed). The literal "@Name" in
+-- transcription_blocks.text keeps the name visible after a person is deleted;
+-- the sidecar row carries only the link and is removed with the person, so the
+-- read renderer degrades to plain unlinked text. See ADR-032.
 
 CREATE TABLE transcription_block_mentioned_persons (
     block_id      UUID          NOT NULL REFERENCES transcription_blocks(id) ON DELETE CASCADE,

backend/src/main/resources/db/migration/V71__person_delete_on_delete_fk.sql

@@ -0,0 +1,50 @@
+-- Move person-delete referential integrity from application code into the database (#684).
+--
+-- Before this migration, PersonService.deletePerson nulled documents.sender_id and removed
+-- document_receivers rows in Java before deleting the person, because the two V1 FKs into
+-- persons had no ON DELETE behaviour. Any other delete path (a future endpoint, a manual
+-- psql, a batch job) could still orphan rows or 500. This migration makes the database the
+-- single source of truth so a person delete is safe from every path.
+--
+-- Cascade boundary: the cascade stays STRICTLY at the join/reference layer and NEVER reaches
+-- documents rows — a cascade into documents would destroy historical letters. sender_id is
+-- SET NULL (documents.senderText preserves the raw textual attribution); the receiver join
+-- row and the @-mention sidecar row are dropped.
+--
+-- No NOT VALID + VALIDATE two-step: these tables are small (thousands of rows → sub-second
+-- ACCESS EXCLUSIVE lock). Do NOT copy this drop-and-recreate pattern onto a large table.
+--
+-- Not audit-logged: a DB ON DELETE cascade runs below AuditService — a known, accepted trade.
+-- The person-delete action itself is still logged at the service layer.
+
+-- documents.sender_id → ON DELETE SET NULL (deleted sender clears the link; the document survives).
+ALTER TABLE public.documents
+    DROP CONSTRAINT fkl5xhww7es3b4um01vmly4y18m,
+    ADD CONSTRAINT fkl5xhww7es3b4um01vmly4y18m
+        FOREIGN KEY (sender_id) REFERENCES public.persons(id) ON DELETE SET NULL;
+
+-- document_receivers.person_id → ON DELETE CASCADE (drop the join row), the symmetric
+-- completion of V14, which added the same to the document_id side of this table.
+ALTER TABLE public.document_receivers
+    DROP CONSTRAINT fkcg7r68qvosqricx1betgrlt7s,
+    ADD CONSTRAINT fkcg7r68qvosqricx1betgrlt7s
+        FOREIGN KEY (person_id) REFERENCES public.persons(id) ON DELETE CASCADE;
+
+-- Soft reference fix: transcription_block_mentioned_persons.person_id was a UUID with no FK
+-- (V56), so deleting a person left dangling mention rows. Give it a real FK with CASCADE.
+-- Clean up pre-existing orphans first — production likely holds dangling rows because the old
+-- deletePerson never cleaned mention rows, and the ADD CONSTRAINT validation scan fails on them.
+-- A DO block with RAISE NOTICE surfaces the purge count: Flyway runs each statement via JDBC
+-- and discards a trailing SELECT's result set, so a "SELECT count(*)" would log nothing.
+DO $$
+DECLARE removed int;
+BEGIN
+    DELETE FROM transcription_block_mentioned_persons m
+    WHERE NOT EXISTS (SELECT 1 FROM persons p WHERE p.id = m.person_id);
+    GET DIAGNOSTICS removed = ROW_COUNT;
+    RAISE NOTICE 'V71 orphaned_mention_rows_removed=%', removed;
+END $$;
+
+ALTER TABLE public.transcription_block_mentioned_persons
+    ADD CONSTRAINT fk_tbmp_person
+        FOREIGN KEY (person_id) REFERENCES public.persons(id) ON DELETE CASCADE;

backend/src/test/java/org/raddatz/familienarchiv/person/PersonRepositoryTest.java

@@ -21,6 +21,7 @@ import jakarta.persistence.PersistenceContext;
 import java.util.List;
 import java.util.Optional;
 import java.util.Set;
+import java.util.UUID;
 
 import static org.assertj.core.api.Assertions.assertThat;
 
@@ -707,4 +708,133 @@ class PersonRepositoryTest {
         assertThat(found).isPresent();
         assertThat(found.get().getGeneration()).isNull();
     }
+
+    // ─── #684: ON DELETE integrity enforced at the database layer ──────────────
+    // A raw deleteById (bypassing PersonService) must keep referential integrity:
+    // documents.sender_id → SET NULL, document_receivers.person_id → CASCADE, and the
+    // transcription_block_mentioned_persons soft reference → CASCADE. These run against
+    // real Postgres because the FK ON DELETE behaviour never fires on H2.
+
+    @Test
+    void deleteById_personSenderOfAReceiverOfB_nullsSender_dropsReceiverRow_bothDocumentsSurvive() {
+        Person target = personRepository.save(Person.builder().firstName("Weg").lastName("Person").build());
+        Person bystander = personRepository.save(Person.builder().firstName("Bleibt").lastName("Hier").build());
+
+        Document sent = documentRepository.save(Document.builder()
+                .title("Gesendet").originalFilename("sent.pdf")
+                .status(DocumentStatus.UPLOADED).sender(target).build());
+        Document received = documentRepository.save(Document.builder()
+                .title("Empfangen").originalFilename("received.pdf")
+                .status(DocumentStatus.UPLOADED).sender(bystander)
+                .receivers(Set.of(target)).build());
+        entityManager.flush();
+        entityManager.clear();
+
+        personRepository.deleteById(target.getId());
+        entityManager.flush();
+        entityManager.clear();
+
+        assertThat(personRepository.findById(target.getId())).isEmpty();
+
+        Document reloadedSent = documentRepository.findById(sent.getId()).orElseThrow();
+        assertThat(reloadedSent.getSender()).isNull(); // AC-1: SET NULL
+
+        Document reloadedReceived = documentRepository.findById(received.getId()).orElseThrow();
+        assertThat(reloadedReceived.getReceivers())
+                .noneMatch(p -> p.getId().equals(target.getId())); // AC-2: CASCADE drops the join row
+
+        // Cascade-boundary guard (Nora, non-negotiable): the cascade stops at the join/reference
+        // layer — both documents themselves survive. Guards against a future migration turning
+        // documents.sender_id SET NULL into CASCADE and destroying historical letters.
+        assertThat(documentRepository.findById(sent.getId())).isPresent();
+        assertThat(documentRepository.findById(received.getId())).isPresent();
+    }
+
+    @Test
+    void deleteById_receiverWithCoReceiver_dropsOnlyDeletedPersonsJoinRow() {
+        Person target = personRepository.save(Person.builder().firstName("Weg").lastName("Person").build());
+        Person coReceiver = personRepository.save(Person.builder().firstName("Mit").lastName("Empfänger").build());
+        Person sender = personRepository.save(Person.builder().firstName("Send").lastName("Er").build());
+
+        Document doc = documentRepository.save(Document.builder()
+                .title("Brief").originalFilename("brief.pdf")
+                .status(DocumentStatus.UPLOADED).sender(sender)
+                .receivers(Set.of(target, coReceiver)).build());
+        entityManager.flush();
+        entityManager.clear();
+
+        personRepository.deleteById(target.getId());
+        entityManager.flush();
+        entityManager.clear();
+
+        Document reloaded = documentRepository.findById(doc.getId()).orElseThrow();
+        assertThat(reloaded.getReceivers()).extracting(Person::getId)
+                .containsExactly(coReceiver.getId()); // co-receiver untouched
+    }
+
+    @Test
+    void deleteById_personIsSenderAndReceiverOfSameDocument_documentSurvives_senderNull_receiverDropped() {
+        // AC-8: the trickier same-document interaction the cross-document cases don't exercise.
+        Person target = personRepository.save(Person.builder().firstName("Beides").lastName("Person").build());
+        Person coReceiver = personRepository.save(Person.builder().firstName("Mit").lastName("Empfänger").build());
+
+        Document doc = documentRepository.save(Document.builder()
+                .title("Selbstbrief").originalFilename("self.pdf")
+                .status(DocumentStatus.UPLOADED).sender(target)
+                .receivers(Set.of(target, coReceiver)).build());
+        entityManager.flush();
+        entityManager.clear();
+
+        personRepository.deleteById(target.getId());
+        entityManager.flush();
+        entityManager.clear();
+
+        Document reloaded = documentRepository.findById(doc.getId()).orElseThrow();
+        assertThat(reloaded.getSender()).isNull();
+        assertThat(reloaded.getReceivers()).extracting(Person::getId)
+                .containsExactly(coReceiver.getId());
+    }
+
+    @Test
+    void deleteById_mentionedPerson_dropsMentionRow_blockTextSurvives() {
+        // AC-3: the @-mention sidecar is a CASCADE soft reference, but the literal "@Name" lives
+        // in transcription_blocks.text and must stay visible as plain text after the person goes.
+        Person mentioned = personRepository.save(Person.builder().firstName("Auguste").lastName("Raddatz").build());
+        Document doc = documentRepository.save(Document.builder()
+                .title("Brief").originalFilename("brief.pdf")
+                .status(DocumentStatus.UPLOADED).build());
+        entityManager.flush();
+
+        UUID annotationId = UUID.randomUUID();
+        UUID blockId = UUID.randomUUID();
+        entityManager.createNativeQuery(
+                "INSERT INTO document_annotations (id, document_id, page_number, x, y, width, height, color) "
+                        + "VALUES (?1, ?2, 1, 0.1, 0.2, 0.3, 0.1, '#fff')")
+                .setParameter(1, annotationId).setParameter(2, doc.getId()).executeUpdate();
+        entityManager.createNativeQuery(
+                "INSERT INTO transcription_blocks (id, annotation_id, document_id, text) VALUES (?1, ?2, ?3, ?4)")
+                .setParameter(1, blockId).setParameter(2, annotationId).setParameter(3, doc.getId())
+                .setParameter(4, "Brief an @Auguste Raddatz").executeUpdate();
+        entityManager.createNativeQuery(
+                "INSERT INTO transcription_block_mentioned_persons (block_id, person_id, display_name) "
+                        + "VALUES (?1, ?2, ?3)")
+                .setParameter(1, blockId).setParameter(2, mentioned.getId())
+                .setParameter(3, "Auguste Raddatz").executeUpdate();
+        entityManager.flush();
+        entityManager.clear();
+
+        personRepository.deleteById(mentioned.getId());
+        entityManager.flush();
+        entityManager.clear();
+
+        Number mentionRows = (Number) entityManager.createNativeQuery(
+                "SELECT count(*) FROM transcription_block_mentioned_persons WHERE person_id = ?1")
+                .setParameter(1, mentioned.getId()).getSingleResult();
+        assertThat(mentionRows.longValue()).isZero();
+
+        String text = (String) entityManager.createNativeQuery(
+                "SELECT text FROM transcription_blocks WHERE id = ?1")
+                .setParameter(1, blockId).getSingleResult();
+        assertThat(text).isEqualTo("Brief an @Auguste Raddatz");
+    }
 }