backend/src/main/java/org/raddatz/familienarchiv/person/PersonRepository.java

@@ -29,14 +29,36 @@ public interface PersonRepository extends JpaRepository<Person, UUID> {
     // Stammbaum-Knoten: alle Personen mit family_member = true.
     List<Person> findByFamilyMemberTrueOrderByLastNameAscFirstNameAsc();
 
-    // Lookup by full alias string, used during ODS mass import
-    Optional<Person> findByAliasIgnoreCase(String alias);
+    // Exact-case alias lookup — the first resolution step in findOrCreateByAlias.
+    // Case-colliding aliases across persons (müller / Müller) are valid human labels, NOT
+    // duplicates: source_ref is the stable identity (ADR-025/033), alias is editable. Do NOT
+    // add a unique(lower(alias)) constraint — see ADR-033.
+    Optional<Person> findByAlias(String alias);
+
+    // Plural case-insensitive alias lookup — the fallback step. Returns ALL case-folding
+    // siblings so the service can pick a deterministic one (lowest id) instead of letting a
+    // derived Optional<…>IgnoreCase throw NonUniqueResultException. See ADR-033.
+    List<Person> findAllByAliasIgnoreCase(String alias);
 
     // Lookup by the normalizer person_id, used for idempotent canonical re-import (Phase 3).
     Optional<Person> findBySourceRef(String sourceRef);
 
-    // Exact first+last name match, used for filename-based sender lookup
-    Optional<Person> findByFirstNameIgnoreCaseAndLastNameIgnoreCase(String firstName, String lastName);
+    // Exact-case first+last name match — the first step of filename-based sender resolution.
+    // Explicit `=` (HQL, not a derived query) so a null firstName binds as `first_name = NULL`
+    // — never a match — instead of the derived-query fold to `first_name IS NULL`, which would
+    // pull a last-name-only row in as a sender (a provenance defect). See ADR-033.
+    @Query("SELECT p FROM Person p WHERE p.firstName = :firstName AND p.lastName = :lastName")
+    Optional<Person> findByFirstNameAndLastName(@Param("firstName") String firstName,
+                                                @Param("lastName") String lastName);
+
+    // Plural case-insensitive first+last name match — lets findByName bail to empty on 2+ matches
+    // instead of letting a derived Optional<…>IgnoreCase throw NonUniqueResultException. Same
+    // null fail-closed guarantee as above: LOWER(:firstName) is NULL for a null arg, so a null
+    // first name resolves to no match (not first_name IS NULL widening). See ADR-033.
+    @Query("SELECT p FROM Person p WHERE LOWER(p.firstName) = LOWER(:firstName) "
+         + "AND LOWER(p.lastName) = LOWER(:lastName)")
+    List<Person> findAllByFirstNameIgnoreCaseAndLastNameIgnoreCase(@Param("firstName") String firstName,
+                                                                   @Param("lastName") String lastName);
 
     // --- PersonSummaryDTO with document count ---
 

backend/src/main/java/org/raddatz/familienarchiv/person/PersonService.java

@@ -1,5 +1,6 @@
 package org.raddatz.familienarchiv.person;
 
+import java.util.Comparator;
 import java.util.List;
 import java.util.Optional;
 import java.util.UUID;
@@ -110,7 +111,19 @@ public class PersonService {
     }
 
     public Optional<Person> findByName(String firstName, String lastName) {
-        return personRepository.findByFirstNameIgnoreCaseAndLastNameIgnoreCase(firstName, lastName);
+        // Same scope as findOrCreateByAlias (#731): a case-collision resolves without throwing;
+        // two byte-identical same-case persons are an out-of-scope data anomaly the exact
+        // Optional below would surface as the opaque INTERNAL_ERROR, not a wrong sender.
+        Optional<Person> exact = personRepository.findByFirstNameAndLastName(firstName, lastName);
+        if (exact.isPresent()) return exact;
+        List<Person> caseInsensitive =
+                personRepository.findAllByFirstNameIgnoreCaseAndLastNameIgnoreCase(firstName, lastName);
+        // Deliberate divergence from findOrCreateByAlias: an ambiguous filename leaves the sender
+        // UNSET rather than picking the lowest id. The archive's value is correct provenance — a
+        // confidently-wrong pre-filled "Hans Müller" is worse than an empty field, because a
+        // reviewer won't re-check a pre-filled value. Do NOT "consistency-clean" this into the
+        // lowest-id fallback. See ADR-033.
+        return caseInsensitive.size() == 1 ? Optional.of(caseInsensitive.get(0)) : Optional.empty();
     }
 
     /** Lookup by the normalizer person_id — used by the canonical importer for register-first matching. */
@@ -125,32 +138,45 @@ public class PersonService {
         PersonType type = PersonTypeClassifier.classify(alias);
         if (type == PersonType.SKIP) return null;
 
-        return personRepository.findByAliasIgnoreCase(alias).orElseGet(() -> {
-            if (type == PersonType.INSTITUTION || type == PersonType.GROUP) {
-                return personRepository.save(Person.builder()
-                        .alias(alias)
-                        .lastName(alias)
-                        .personType(type)
-                        .build());
-            }
+        // Aliases differing only by case (müller / Müller) are valid distinct persons, not
+        // duplicates, so a CASE-COLLISION must not throw: exact-case first, then the lowest-id
+        // case-insensitive sibling, then create. Mirrors the tag path — see ADR-033.
+        // Scope (#731): "ambiguous" means case-insensitive. Two BYTE-IDENTICAL same-case aliases
+        // are a true data anomaly out of scope here; the exact Optional below would surface that
+        // as the opaque INTERNAL_ERROR (never a wrong row), not silently pick one.
+        Optional<Person> exact = personRepository.findByAlias(alias);
+        if (exact.isPresent()) return exact.get();              // exact-case wins
+        List<Person> caseInsensitive = personRepository.findAllByAliasIgnoreCase(alias);
+        if (!caseInsensitive.isEmpty()) {
+            return caseInsensitive.stream().min(Comparator.comparing(Person::getId)).orElseThrow(); // deterministic tie-break — list is non-empty, never throws
+        }
 
-            PersonNameParser.SplitName split = PersonNameParser.split(alias);
-            Person person = personRepository.save(Person.builder()
+        // Create-when-absent: institution/group keep the full label in lastName; a person name
+        // is split and a maiden name (geb. …) becomes a MAIDEN_NAME alias.
+        if (type == PersonType.INSTITUTION || type == PersonType.GROUP) {
+            return personRepository.save(Person.builder()
                     .alias(alias)
-                    .firstName(split.firstName())
-                    .lastName(split.lastName())
+                    .lastName(alias)
+                    .personType(type)
                     .build());
-            if (split.maidenName() != null) {
-                int nextSortOrder = aliasRepository.findMaxSortOrder(person.getId()) + 1;
-                aliasRepository.save(PersonNameAlias.builder()
-                        .person(person)
-                        .lastName(split.maidenName())
-                        .type(PersonNameAliasType.MAIDEN_NAME)
-                        .sortOrder(nextSortOrder)
-                        .build());
-            }
-            return person;
-        });
+        }
+
+        PersonNameParser.SplitName split = PersonNameParser.split(alias);
+        Person person = personRepository.save(Person.builder()
+                .alias(alias)
+                .firstName(split.firstName())
+                .lastName(split.lastName())
+                .build());
+        if (split.maidenName() != null) {
+            int nextSortOrder = aliasRepository.findMaxSortOrder(person.getId()) + 1;
+            aliasRepository.save(PersonNameAlias.builder()
+                    .person(person)
+                    .lastName(split.maidenName())
+                    .type(PersonNameAliasType.MAIDEN_NAME)
+                    .sortOrder(nextSortOrder)
+                    .build());
+        }
+        return person;
     }
 
     /**

backend/src/main/java/org/raddatz/familienarchiv/person/README.md

@@ -20,8 +20,8 @@ Features: person CRUD, name alias management, person merge (deduplication), fami
 | `getById(UUID)` | document, geschichte, ocr | Fetch one person by ID |
 | `getAllById(List<UUID>)` | document | Bulk fetch for sender/receiver resolution |
 | `findAll(String q)` | document, dashboard | List all persons |
-| `findByName(String firstName, String lastName)` | document | Typeahead search |
-| `findOrCreateByAlias(String rawName)` | importing | Idempotent create during mass import; type classification happens internally |
+| `findByName(String firstName, String lastName)` | document | Filename-based **sender resolution** in `storeDocument`: exact-case match → single case-insensitive match → else **empty** (ambiguous names leave the sender unset; a null first name never matches). See ADR-033. |
+| `findOrCreateByAlias(String rawName)` | importing | Idempotent create during mass import; type classification happens internally. Resolves exact-case → lowest-id case-insensitive sibling → create — never throws on case-colliding aliases. See ADR-033. |
 | `findAllFamilyMembers()` | dashboard | Family member list for stats |
 | `findCorrespondents()` | document | Correspondent list for conversation filter |
 | `count()` | dashboard | Total person count for stats |

backend/src/test/java/org/raddatz/familienarchiv/exception/GlobalExceptionHandlerTest.java

@@ -12,6 +12,7 @@ import org.mockito.MockedStatic;
 import org.mockito.junit.jupiter.MockitoExtension;
 import org.slf4j.LoggerFactory;
 import org.springframework.dao.DataIntegrityViolationException;
+import org.springframework.dao.IncorrectResultSizeDataAccessException;
 import org.springframework.http.ResponseEntity;
 
 import static org.assertj.core.api.Assertions.assertThat;
@@ -37,6 +38,30 @@ class GlobalExceptionHandlerTest {
         }
     }
 
+    @Test
+    void handleGeneric_incorrectResultSize_staysOpaque_noHibernateOrRowCountLeak() {
+        // #731: before the fix, a case-colliding alias/name made Hibernate throw
+        // NonUniqueResultException → IncorrectResultSizeDataAccessException, which has no
+        // dedicated handler and falls through to handleGeneric. The fix removes the throw, but
+        // this pins the handler: a stray one must stay opaque — no Hibernate class name, no SQL,
+        // no "2 results were returned" row count reaching the client (CWE-209).
+        IncorrectResultSizeDataAccessException ex = new IncorrectResultSizeDataAccessException(
+                "query did not return a unique result: 2 results were returned", 1, 2);
+
+        try (MockedStatic<Sentry> sentryMock = mockStatic(Sentry.class)) {
+            ResponseEntity<GlobalExceptionHandler.ErrorResponse> response = handler.handleGeneric(ex);
+
+            assertThat(response.getStatusCode().value()).isEqualTo(500);
+            assertThat(response.getBody()).isNotNull();
+            assertThat(response.getBody().code()).isEqualTo(ErrorCode.INTERNAL_ERROR);
+            assertThat(response.getBody().message())
+                    .isEqualTo("An unexpected error occurred")
+                    .doesNotContain("results were returned")
+                    .doesNotContain("NonUnique")
+                    .doesNotContain("IncorrectResultSize");
+        }
+    }
+
     @Test
     void handleDataIntegrityViolation_returns400_withoutLeakingConstraint_orSentry() {
         // A DataIntegrityViolationException carries the constraint name + SQL in its message;

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

@@ -121,37 +121,60 @@ class PersonRepositoryTest {
                 .containsExactly("Anna", "Clara");
     }
 
-    // ─── findByAliasIgnoreCase ────────────────────────────────────────────────
+    // ─── findByAlias (exact) / findAllByAliasIgnoreCase (case-folding siblings) ───
 
     @Test
-    void findByAliasIgnoreCase_returnsMatchingPerson() {
+    void findByAlias_returnsExactCaseMatchOnly() {
         personRepository.save(Person.builder()
                 .firstName("Karl").lastName("Brandt").alias("Opa Karl").build());
 
-        Optional<Person> found = personRepository.findByAliasIgnoreCase("opa karl");
-
-        assertThat(found).isPresent();
-        assertThat(found.get().getFirstName()).isEqualTo("Karl");
+        assertThat(personRepository.findByAlias("Opa Karl")).isPresent();
+        assertThat(personRepository.findByAlias("opa karl")).isEmpty(); // exact-case: a folded form does NOT match
     }
 
     @Test
-    void findByAliasIgnoreCase_returnsEmpty_whenAliasDoesNotMatch() {
-        Optional<Person> found = personRepository.findByAliasIgnoreCase("nobody");
-
-        assertThat(found).isEmpty();
+    void findAllByAliasIgnoreCase_returnsEmpty_whenAliasDoesNotMatch() {
+        assertThat(personRepository.findAllByAliasIgnoreCase("nobody")).isEmpty();
     }
 
-    // ─── findByFirstNameIgnoreCaseAndLastNameIgnoreCase ───────────────────────
+    @Test
+    void findAllByAliasIgnoreCase_foldsUmlautCase_inRealPostgres() {
+        // Proves Postgres LOWER() folds ü the same way for both rows — a plain-ASCII probe would
+        // stay green even if umlaut folding regressed. Both case-colliding aliases must match.
+        personRepository.save(Person.builder().lastName("Müller").alias("Müller").build());
+        personRepository.save(Person.builder().lastName("müller").alias("müller").build());
+
+        assertThat(personRepository.findAllByAliasIgnoreCase("MÜLLER")).hasSize(2);
+    }
+
+    // ─── findByFirstNameAndLastName (exact) / findAllByFirstNameIgnoreCaseAndLastNameIgnoreCase ───
 
     @Test
-    void findByFirstNameIgnoreCaseAndLastNameIgnoreCase_returnsMatch() {
+    void findByFirstNameAndLastName_returnsExactCaseMatchOnly() {
         personRepository.save(Person.builder().firstName("Maria").lastName("Raddatz").build());
 
-        Optional<Person> found = personRepository.findByFirstNameIgnoreCaseAndLastNameIgnoreCase(
-                "maria", "raddatz");
+        assertThat(personRepository.findByFirstNameAndLastName("Maria", "Raddatz")).isPresent();
+        assertThat(personRepository.findByFirstNameAndLastName("maria", "raddatz")).isEmpty(); // exact-case only
+    }
 
-        assertThat(found).isPresent();
-        assertThat(found.get().getFirstName()).isEqualTo("Maria");
+    @Test
+    void findAllByFirstNameIgnoreCaseAndLastNameIgnoreCase_foldsUmlautCase_inRealPostgres() {
+        personRepository.save(Person.builder().firstName("Hans").lastName("Müller").build());
+        personRepository.save(Person.builder().firstName("hans").lastName("müller").build());
+
+        assertThat(personRepository.findAllByFirstNameIgnoreCaseAndLastNameIgnoreCase("HANS", "MÜLLER"))
+                .hasSize(2);
+    }
+
+    @Test
+    void findAllByFirstNameIgnoreCaseAndLastNameIgnoreCase_nullFirstName_foldsToNoMatch() {
+        // Fail-closed: a last-name-only filename (null first name) must NOT widen to first_name IS
+        // NULL and pull in the institution/last-name-only row as a "sender". Proven on real
+        // Postgres because a mocked unit test cannot catch the IS NULL vs `= NULL` semantics.
+        personRepository.save(Person.builder().lastName("Müller").build()); // first_name NULL
+
+        assertThat(personRepository.findAllByFirstNameIgnoreCaseAndLastNameIgnoreCase(null, "Müller"))
+                .isEmpty();
     }
 
     // ─── findCorrespondents ───────────────────────────────────────────────────

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

@@ -4,6 +4,7 @@ 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.DocumentService;
 import org.raddatz.familienarchiv.document.DocumentStatus;
 import org.raddatz.familienarchiv.person.Person;
 import org.raddatz.familienarchiv.person.PersonType;
@@ -16,10 +17,13 @@ import org.springframework.test.context.bean.override.mockito.MockitoBean;
 import org.springframework.transaction.annotation.Transactional;
 import software.amazon.awssdk.services.s3.S3Client;
 
+import org.springframework.mock.web.MockMultipartFile;
+
 import jakarta.persistence.EntityManager;
 import jakarta.persistence.PersistenceContext;
 
 import java.util.Set;
+import java.util.UUID;
 
 import static org.assertj.core.api.Assertions.assertThat;
 
@@ -33,6 +37,7 @@ class PersonServiceIntegrationTest {
     @Autowired PersonService personService;
     @Autowired PersonRepository personRepository;
     @Autowired DocumentRepository documentRepository;
+    @Autowired DocumentService documentService;
 
     @PersistenceContext EntityManager entityManager;
 
@@ -75,6 +80,93 @@ class PersonServiceIntegrationTest {
         assertThat(result.getLastName()).isEqualTo("Cram");
     }
 
+    // ─── #731: case-colliding alias resolution against real Postgres ───────────
+    // The umlaut pair is mandatory — only the real DB proves Postgres LOWER() folds ü; a
+    // plain-ASCII test would stay green while umlaut aliases regressed.
+
+    @Test
+    void findOrCreateByAlias_resolvesUmlautAliasCollision_toLowestId_withoutThrow() {
+        Person muller = personRepository.save(Person.builder().lastName("Müller").alias("Müller").build());
+        Person mullerLower = personRepository.save(Person.builder().lastName("müller").alias("müller").build());
+        UUID expected = muller.getId().compareTo(mullerLower.getId()) <= 0 ? muller.getId() : mullerLower.getId();
+
+        // No exact-case "MÜLLER" row → falls through to the case-insensitive branch with two
+        // candidates and must pick the lowest id, never throwing NonUniqueResultException.
+        Person resolved = personService.findOrCreateByAlias("MÜLLER");
+
+        assertThat(resolved.getId()).isEqualTo(expected);
+    }
+
+    @Test
+    void findOrCreateByAlias_umlautAliasCollision_isDeterministicAcrossCalls() {
+        personRepository.save(Person.builder().lastName("Müller").alias("Müller").build());
+        personRepository.save(Person.builder().lastName("müller").alias("müller").build());
+
+        Person first = personService.findOrCreateByAlias("MÜLLER");
+        Person second = personService.findOrCreateByAlias("MÜLLER");
+
+        assertThat(second.getId()).isEqualTo(first.getId());
+    }
+
+    // ─── #731: filename-based sender resolution against real Postgres ──────────
+
+    @Test
+    void storeDocument_resolvesSender_whenFilenameNameIsUnique() throws Exception {
+        Person hans = personRepository.save(Person.builder().firstName("Hans").lastName("Müller").build());
+
+        Document doc = uploadNamed("1965-03-12_Müller_Hans.pdf").document();
+
+        assertThat(doc.getSender()).isNotNull();
+        assertThat(doc.getSender().getId()).isEqualTo(hans.getId());
+    }
+
+    @Test
+    void storeDocument_resolvesSender_onSingleCaseInsensitiveMatch() throws Exception {
+        Person hans = personRepository.save(Person.builder().firstName("Hans").lastName("Müller").build());
+
+        // Filename folds to "hans müller"; the only stored person is "Hans Müller".
+        Document doc = uploadNamed("1965-03-12_müller_hans.pdf").document();
+
+        assertThat(doc.getSender()).isNotNull();
+        assertThat(doc.getSender().getId()).isEqualTo(hans.getId());
+    }
+
+    @Test
+    void storeDocument_leavesSenderUnset_whenFilenameNameIsAmbiguous() throws Exception {
+        // Two persons collide case-insensitively; the filename casing ("HANS"/"MÜLLER") matches
+        // neither exactly → no exact-case winner → bail to null (never an arbitrary guess), no 500.
+        personRepository.save(Person.builder().firstName("Hans").lastName("Müller").build());
+        personRepository.save(Person.builder().firstName("hans").lastName("müller").build());
+
+        Document doc = uploadNamed("1965-03-12_MÜLLER_HANS.pdf").document();
+
+        assertThat(doc.getSender()).isNull();
+    }
+
+    @Test
+    void storeDocument_leavesSenderUnset_whenFilenameHasNoFirstName() throws Exception {
+        // A last-name-only filename never resolves to a sender (the parser yields no parsed name).
+        personRepository.save(Person.builder().lastName("Müller").build());
+
+        Document doc = uploadNamed("1965-03-12_Müller.pdf").document();
+
+        assertThat(doc.getSender()).isNull();
+    }
+
+    @Test
+    void findByName_nullFirstName_resolvesToEmpty_inRealPostgres() {
+        // Fail-closed against the real DB: a null first name must NOT widen to first_name IS NULL
+        // and pick up the last-name-only row.
+        personRepository.save(Person.builder().lastName("Müller").build()); // first_name NULL
+
+        assertThat(personService.findByName(null, "Müller")).isEmpty();
+    }
+
+    private DocumentService.StoreResult uploadNamed(String filename) throws Exception {
+        MockMultipartFile file = new MockMultipartFile("file", filename, "application/pdf", new byte[]{1, 2, 3});
+        return documentService.storeDocument(file, null);
+    }
+
     // ─── #667: confirm round-trip + reader-default semantics ──────────────────
 
     @Test

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

@@ -375,14 +375,57 @@ class PersonServiceTest {
     // ─── findOrCreateByAlias ─────────────────────────────────────────────────
 
     @Test
-    void findOrCreateByAlias_returnsExisting_whenAliasFound() {
-        String alias = "Walter de Gruyter";
-        Person existing = Person.builder().id(UUID.randomUUID()).alias(alias).build();
-        when(personRepository.findByAliasIgnoreCase(alias)).thenReturn(Optional.of(existing));
+    void findOrCreateByAlias_returnsExactCaseMatch_overCaseInsensitiveSibling() {
+        String alias = "müller";
+        Person exact = Person.builder().id(UUID.randomUUID()).alias("müller").build();
+        when(personRepository.findByAlias(alias)).thenReturn(Optional.of(exact));
 
         Person result = personService.findOrCreateByAlias(alias);
 
-        assertThat(result).isEqualTo(existing);
+        assertThat(result).isEqualTo(exact);
+        verify(personRepository, never()).findAllByAliasIgnoreCase(any());
+        verify(personRepository, never()).save(any());
+    }
+
+    @Test
+    void findOrCreateByAlias_returnsExactCaseMatch_evenWhenMultipleSiblingsCollide() {
+        String alias = "Müller";
+        Person exact = Person.builder().id(UUID.randomUUID()).alias("Müller").build();
+        when(personRepository.findByAlias(alias)).thenReturn(Optional.of(exact));
+
+        Person result = personService.findOrCreateByAlias(alias);
+
+        assertThat(result).isEqualTo(exact);
+        // exact-case short-circuits — the case-insensitive siblings are never consulted.
+        verify(personRepository, never()).findAllByAliasIgnoreCase(any());
+    }
+
+    @Test
+    void findOrCreateByAlias_usesSingleCaseInsensitiveMatch_whenNoExactCase() {
+        String alias = "müller";
+        Person only = Person.builder().id(UUID.randomUUID()).alias("Müller").build();
+        when(personRepository.findByAlias(alias)).thenReturn(Optional.empty());
+        when(personRepository.findAllByAliasIgnoreCase(alias)).thenReturn(List.of(only));
+
+        Person result = personService.findOrCreateByAlias(alias);
+
+        assertThat(result).isEqualTo(only);
+        verify(personRepository, never()).save(any());
+    }
+
+    @Test
+    void findOrCreateByAlias_returnsLowestIdDeterministically_whenMultipleCaseInsensitiveMatches() {
+        String alias = "müller";
+        Person lower = Person.builder().id(UUID.fromString("00000000-0000-0000-0000-000000000001")).alias("Müller").build();
+        Person higher = Person.builder().id(UUID.fromString("00000000-0000-0000-0000-000000000002")).alias("müller").build();
+        when(personRepository.findByAlias(alias)).thenReturn(Optional.empty());
+        when(personRepository.findAllByAliasIgnoreCase(alias)).thenReturn(List.of(higher, lower)); // unordered
+
+        Person first = personService.findOrCreateByAlias(alias);
+        Person second = personService.findOrCreateByAlias(alias);
+
+        assertThat(first.getId()).isEqualTo(lower.getId());      // lowest id wins
+        assertThat(second.getId()).isEqualTo(first.getId());     // same result every call — never throws
         verify(personRepository, never()).save(any());
     }
 
@@ -390,7 +433,8 @@ class PersonServiceTest {
     void findOrCreateByAlias_createsNew_whenAliasNotFound() {
         String alias = "Clara Cram";
         Person saved = Person.builder().id(UUID.randomUUID()).alias(alias).firstName("Clara").lastName("Cram").build();
-        when(personRepository.findByAliasIgnoreCase(alias)).thenReturn(Optional.empty());
+        when(personRepository.findByAlias(alias)).thenReturn(Optional.empty());
+        when(personRepository.findAllByAliasIgnoreCase(alias)).thenReturn(List.of());
         when(personRepository.save(any())).thenReturn(saved);
 
         Person result = personService.findOrCreateByAlias(alias);
@@ -403,7 +447,8 @@ class PersonServiceTest {
     void findOrCreateByAlias_createsMaidenNameAlias_whenGebPresent() {
         String alias = "Clara Cram geb. de Gruyter";
         Person saved = Person.builder().id(UUID.randomUUID()).alias(alias).firstName("Clara").lastName("Cram").build();
-        when(personRepository.findByAliasIgnoreCase(alias)).thenReturn(Optional.empty());
+        when(personRepository.findByAlias(alias)).thenReturn(Optional.empty());
+        when(personRepository.findAllByAliasIgnoreCase(alias)).thenReturn(List.of());
         when(personRepository.save(any())).thenReturn(saved);
         when(aliasRepository.findMaxSortOrder(saved.getId())).thenReturn(0);
         when(aliasRepository.save(any())).thenAnswer(inv -> inv.getArgument(0));
@@ -425,7 +470,8 @@ class PersonServiceTest {
     @Test
     void findOrCreateByAlias_setsInstitutionType_withFullNameInLastName() {
         String alias = "Arthur Collignon GmbH";
-        when(personRepository.findByAliasIgnoreCase(alias)).thenReturn(Optional.empty());
+        when(personRepository.findByAlias(alias)).thenReturn(Optional.empty());
+        when(personRepository.findAllByAliasIgnoreCase(alias)).thenReturn(List.of());
         when(personRepository.save(any())).thenAnswer(inv -> {
             Person p = inv.getArgument(0);
             p.setId(UUID.randomUUID());
@@ -442,7 +488,8 @@ class PersonServiceTest {
     @Test
     void findOrCreateByAlias_setsGroupType_withFullNameInLastName() {
         String alias = "Geschwister de Gruyter";
-        when(personRepository.findByAliasIgnoreCase(alias)).thenReturn(Optional.empty());
+        when(personRepository.findByAlias(alias)).thenReturn(Optional.empty());
+        when(personRepository.findAllByAliasIgnoreCase(alias)).thenReturn(List.of());
         when(personRepository.save(any())).thenAnswer(inv -> {
             Person p = inv.getArgument(0);
             p.setId(UUID.randomUUID());
@@ -460,7 +507,8 @@ class PersonServiceTest {
     void findOrCreateByAlias_noAlias_whenNoGeb() {
         String alias = "Clara Cram";
         Person saved = Person.builder().id(UUID.randomUUID()).alias(alias).firstName("Clara").lastName("Cram").build();
-        when(personRepository.findByAliasIgnoreCase(alias)).thenReturn(Optional.empty());
+        when(personRepository.findByAlias(alias)).thenReturn(Optional.empty());
+        when(personRepository.findAllByAliasIgnoreCase(alias)).thenReturn(List.of());
         when(personRepository.save(any())).thenReturn(saved);
 
         personService.findOrCreateByAlias(alias);
@@ -472,11 +520,54 @@ class PersonServiceTest {
     void findOrCreateByAlias_trimsInput() {
         String alias = "  Clara Cram  ";
         Person saved = Person.builder().id(UUID.randomUUID()).alias("Clara Cram").build();
-        when(personRepository.findByAliasIgnoreCase("Clara Cram")).thenReturn(Optional.of(saved));
+        when(personRepository.findByAlias("Clara Cram")).thenReturn(Optional.of(saved));
 
         personService.findOrCreateByAlias(alias);
 
-        verify(personRepository).findByAliasIgnoreCase("Clara Cram");
+        verify(personRepository).findByAlias("Clara Cram");
+    }
+
+    // ─── findByName (filename-based sender resolution) ────────────────────────
+
+    @Test
+    void findByName_returnsExactCaseMatch_overCaseInsensitiveSibling() {
+        Person exact = Person.builder().id(UUID.randomUUID()).firstName("Hans").lastName("Müller").build();
+        when(personRepository.findByFirstNameAndLastName("Hans", "Müller")).thenReturn(Optional.of(exact));
+
+        assertThat(personService.findByName("Hans", "Müller")).contains(exact);
+        verify(personRepository, never()).findAllByFirstNameIgnoreCaseAndLastNameIgnoreCase(any(), any());
+    }
+
+    @Test
+    void findByName_usesSingleCaseInsensitiveMatch_whenNoExactCase() {
+        Person only = Person.builder().id(UUID.randomUUID()).firstName("Hans").lastName("Müller").build();
+        when(personRepository.findByFirstNameAndLastName("hans", "müller")).thenReturn(Optional.empty());
+        when(personRepository.findAllByFirstNameIgnoreCaseAndLastNameIgnoreCase("hans", "müller"))
+                .thenReturn(List.of(only));
+
+        assertThat(personService.findByName("hans", "müller")).contains(only);
+    }
+
+    @Test
+    void findByName_bailsToEmpty_whenTwoOrMoreCaseInsensitiveMatches() {
+        Person a = Person.builder().id(UUID.randomUUID()).firstName("Hans").lastName("Müller").build();
+        Person b = Person.builder().id(UUID.randomUUID()).firstName("hans").lastName("müller").build();
+        when(personRepository.findByFirstNameAndLastName("hans", "müller")).thenReturn(Optional.empty());
+        when(personRepository.findAllByFirstNameIgnoreCaseAndLastNameIgnoreCase("hans", "müller"))
+                .thenReturn(List.of(a, b));
+
+        // Ambiguous sender → unset, never an arbitrary guess (provenance correctness over a
+        // confidently-wrong pre-fill). This is the deliberate divergence from the alias path.
+        assertThat(personService.findByName("hans", "müller")).isEmpty();
+    }
+
+    @Test
+    void findByName_returnsEmpty_whenFirstNameNullFoldsToNoMatch() {
+        when(personRepository.findByFirstNameAndLastName(null, "Müller")).thenReturn(Optional.empty());
+        when(personRepository.findAllByFirstNameIgnoreCaseAndLastNameIgnoreCase(null, "Müller"))
+                .thenReturn(List.of());
+
+        assertThat(personService.findByName(null, "Müller")).isEmpty();
     }
 
     // ─── updatePerson (notes) ────────────────────────────────────────────────

docs/adr/033-tag-name-resolution-tolerates-case-collisions.md

@@ -1,4 +1,4 @@
-# ADR-032 — Tag-name resolution tolerates case-collisions: exact-case first, then a deterministic lowest-id fallback, and never a `unique(lower(name))` constraint
+# ADR-033 — Tag-name resolution tolerates case-collisions: exact-case first, then a deterministic lowest-id fallback, and never a `unique(lower(name))` constraint
 
 **Date:** 2026-06-06
 **Status:** Accepted
@@ -82,15 +82,58 @@ added later.
   `IncorrectResultSizeDataAccessException`, and `GlobalExceptionHandler`'s generic handler maps
   any stray one to `INTERNAL_ERROR` with no Hibernate/SQL leak — so no dedicated handler was
   added.
-- **The sibling Person path is unfixed but tracked.** `PersonService.findOrCreateByAlias`
-  (`findByAliasIgnoreCase`) and `findByFirstNameIgnoreCaseAndLastNameIgnoreCase` carry the same
-  latent `Optional`-non-unique throw on user-influenced names; deferred to #731 rather than
-  widened into this fix.
+- **The sibling Person path is fixed the same way — see the Person extension below (#731).**
 - Postgres `LOWER()` folding of umlauts (`ü`/`ä`) is the actual correctness hinge of the
   fallback and cannot be proven by a mocked repo, so it is pinned by a Testcontainers
   `postgres:16-alpine` test on a `Glückwünsche`/`glückwünsche` pair; a plain-ASCII test would
   stay green while the bug reappeared for umlaut tags.
 
+## Person extension (#731)
+
+The Person domain carried the same latent throw on **two** user-influenced lookup surfaces, and
+is fixed with the same exact-case-first, non-throwing pattern — but with a deliberately
+**different fallback per surface**, because the two paths have different consequences.
+
+- **Alias path — `PersonService.findOrCreateByAlias` — deterministic lowest-id (mirrors tag).**
+  `findByAliasIgnoreCase` (`Optional`) is replaced by `findByAlias` (exact) → `findAllByAliasIgnoreCase`
+  (plural, lowest id) → the existing create-when-absent branch (INSTITUTION/GROUP and the
+  maiden-name alias are preserved verbatim). There is no human in the importer loop and the path
+  creates-on-absent anyway, so a deterministic guess is the right behaviour — exactly like tags.
+
+- **Name/sender path — `PersonService.findByName` — bail to null on ambiguity (the new wrinkle).**
+  Used only by `DocumentService.storeDocument` to resolve the upload **sender** from the parsed
+  filename. `findByFirstNameIgnoreCaseAndLastNameIgnoreCase` (`Optional`) is replaced by
+  `findByFirstNameAndLastName` (exact) → `findAllByFirstNameIgnoreCaseAndLastNameIgnoreCase`
+  (plural). Resolution returns the exact-case match, else the single case-insensitive match, else
+  — on **two or more** matches — **empty**. The sender is left unset rather than guessing.
+
+  **Why this diverges from the alias (and tag) decision:** the archive's value is correct
+  provenance. A confidently-wrong pre-filled `Hans Müller` is worse than an empty field, because a
+  senior reviewer will not re-check a value that is already filled in, whereas an empty sender
+  routes the document into the "needs completion" state (`metadataComplete=false`) for a human to
+  assign. The load-bearing comment at `findByName` records this so a future "consistency cleanup"
+  does not reintroduce the confidently-wrong-sender bug by switching it to lowest-id.
+
+- **Fail-closed on a null first name.** A parsed filename can lack a first name. The two new name
+  methods use explicit HQL equality (`= :firstName`) rather than a derived
+  `…IgnoreCase` query, because Spring Data folds a null derived-query argument to `first_name IS
+  NULL` — which would silently widen the match and pull a last-name-only / institution row in as a
+  "sender" (a quiet provenance-integrity defect). With HQL equality a null binds as `= NULL`,
+  which never matches, so a null first name resolves to **no sender**. This is pinned by a
+  real-Postgres repository test.
+
+- **Scope — "ambiguous" is case-insensitive only.** Both exact-case lookups (`findByAlias`,
+  `findByFirstNameAndLastName`) return `Optional`, so two **byte-identical same-case** rows would
+  still throw `NonUniqueResultException`. That is a true data anomaly, deliberately out of scope
+  (it is not a case-collision), and it surfaces as the opaque `INTERNAL_ERROR` — never a silently
+  wrong row — so it is no worse than any other unexpected error and needs no extra handling here.
+
+- **Same stance as tags otherwise:** no `unique(lower(alias))` / `unique(lower(name))` constraint
+  (collisions are valid human labels; `source_ref` is the stable identity per ADR-025), no
+  merge/dedupe, code-only and reversible, and no shared `resolveExactThenCi(...)` helper — the
+  two Person paths have different fallbacks, so the exact→CI→fallback logic is inlined at each
+  with its load-bearing comment (KISS).
+
 ## Alternatives considered
 
 - **A `unique(lower(name))` index** — rejected: the collisions are valid canonical nodes, and