feat(migration): V73 adds UNIQUE DEFERRABLE and CHECK position > 0 on journey_items

DEFERRABLE INITIALLY DEFERRED allows mid-transaction position swaps
during reorder (checked at COMMIT, not per-row). CHECK (position > 0)
guards against off-by-one in the append path. Both verified by
JourneyItemConstraintsTest via raw pg_constraint query + jdbcTemplate
inserts against a real postgres:16-alpine container.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/src/main/java/org/raddatz/familienarchiv/config/JacksonConfig.java

@@ -1,8 +1,7 @@
 package org.raddatz.familienarchiv.config;
 
-import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.Module;
 import org.openapitools.jackson.nullable.JsonNullableModule;
-import org.springframework.boot.autoconfigure.jackson.Jackson2ObjectMapperBuilderCustomizer;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 
@@ -10,7 +9,7 @@ import org.springframework.context.annotation.Configuration;
 public class JacksonConfig {
 
     @Bean
-    public Jackson2ObjectMapperBuilderCustomizer jsonNullableModule() {
-        return builder -> builder.modulesToInstall(new JsonNullableModule());
+    public Module jsonNullableModule() {
+        return new JsonNullableModule();
     }
 }

backend/src/main/resources/db/migration/V73__add_journey_items_position_constraints.sql

@@ -0,0 +1,19 @@
+-- Adds the two constraints that V72 deferred:
+--   1. UNIQUE(geschichte_id, position) DEFERRABLE INITIALLY DEFERRED
+--      Allows mid-transaction position swaps during reorder (checked at COMMIT, not per-row).
+--      Requires transaction-level or session-level connection pooling (prod uses PgBouncer
+--      in transaction mode — correct today; a future switch to statement-level would silently
+--      break deferred checking at COMMIT).
+--   2. CHECK (position > 0) — defense against off-by-one in the append path.
+--
+-- MUST run in a single transaction; Flyway's default per-migration transaction satisfies this.
+-- Do NOT add executeInTransaction=false or any callback that splits this migration.
+
+ALTER TABLE journey_items
+    ADD CONSTRAINT uq_journey_items_geschichte_position
+        UNIQUE (geschichte_id, position)
+        DEFERRABLE INITIALLY DEFERRED;
+
+ALTER TABLE journey_items
+    ADD CONSTRAINT chk_journey_item_position
+        CHECK (position > 0);

backend/src/test/java/org/raddatz/familienarchiv/geschichte/journeyitem/JourneyItemConstraintsTest.java

@@ -0,0 +1,99 @@
+package org.raddatz.familienarchiv.geschichte.journeyitem;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.raddatz.familienarchiv.PostgresContainerConfig;
+import org.raddatz.familienarchiv.document.Document;
+import org.raddatz.familienarchiv.document.DocumentRepository;
+import org.raddatz.familienarchiv.document.DocumentStatus;
+import org.raddatz.familienarchiv.geschichte.Geschichte;
+import org.raddatz.familienarchiv.geschichte.GeschichteRepository;
+import org.raddatz.familienarchiv.geschichte.GeschichteStatus;
+import org.raddatz.familienarchiv.geschichte.GeschichteType;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.context.annotation.Import;
+import org.springframework.dao.DataIntegrityViolationException;
+import org.springframework.jdbc.core.JdbcTemplate;
+import org.springframework.test.context.ActiveProfiles;
+import org.springframework.test.context.bean.override.mockito.MockitoBean;
+import software.amazon.awssdk.services.s3.S3Client;
+
+import java.util.UUID;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+
+/**
+ * Raw-SQL constraint tests for journey_items — deliberately NOT @Transactional at class level.
+ * A DataIntegrityViolationException inside a class-level @Transactional marks the tx
+ * rollback-only and cascades into TransactionSystemException on teardown.
+ * Each test inserts via jdbcTemplate and uses explicit SQL teardown.
+ */
+@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.NONE)
+@ActiveProfiles("test")
+@Import(PostgresContainerConfig.class)
+class JourneyItemConstraintsTest {
+
+    @MockitoBean
+    S3Client s3Client;
+
+    @Autowired JdbcTemplate jdbcTemplate;
+    @Autowired GeschichteRepository geschichteRepository;
+    @Autowired DocumentRepository documentRepository;
+
+    private UUID geschichteId;
+    private UUID documentId;
+
+    @BeforeEach
+    void seed() {
+        jdbcTemplate.execute("DELETE FROM journey_items");
+        Document doc = documentRepository.save(Document.builder()
+                .title("Constraints-Test-Doc")
+                .originalFilename("ct.pdf")
+                .status(DocumentStatus.UPLOADED)
+                .build());
+        documentId = doc.getId();
+        Geschichte g = geschichteRepository.save(Geschichte.builder()
+                .title("Constraints-Test-Journey")
+                .status(GeschichteStatus.DRAFT)
+                .type(GeschichteType.JOURNEY)
+                .build());
+        geschichteId = g.getId();
+    }
+
+    @Test
+    void unique_constraint_is_deferrable_initially_deferred() {
+        Boolean condeferrable = jdbcTemplate.queryForObject(
+                "SELECT condeferrable FROM pg_constraint WHERE conname = 'uq_journey_items_geschichte_position'",
+                Boolean.class);
+        Boolean condeferred = jdbcTemplate.queryForObject(
+                "SELECT condeferred FROM pg_constraint WHERE conname = 'uq_journey_items_geschichte_position'",
+                Boolean.class);
+        assertThat(condeferrable).as("constraint must be deferrable").isTrue();
+        assertThat(condeferred).as("constraint must be initially deferred").isTrue();
+    }
+
+    @Test
+    void position_check_rejects_nonpositive() {
+        UUID itemId = UUID.randomUUID();
+        assertThatThrownBy(() ->
+                jdbcTemplate.update(
+                        "INSERT INTO journey_items (id, geschichte_id, position, note) VALUES (?, ?, ?, ?)",
+                        itemId, geschichteId, 0, "test"))
+                .isInstanceOf(DataIntegrityViolationException.class);
+    }
+
+    @Test
+    void unique_constraint_rejects_duplicate_position_per_geschichte() {
+        jdbcTemplate.update(
+                "INSERT INTO journey_items (id, geschichte_id, position, document_id) VALUES (?, ?, ?, ?)",
+                UUID.randomUUID(), geschichteId, 10, documentId);
+
+        assertThatThrownBy(() ->
+                jdbcTemplate.update(
+                        "INSERT INTO journey_items (id, geschichte_id, position, document_id) VALUES (?, ?, ?, ?)",
+                        UUID.randomUUID(), geschichteId, 10, documentId))
+                .isInstanceOf(DataIntegrityViolationException.class);
+    }
+}