feat(timeline): add TimelineService assembly + 24-test Mockito suite

Creates TimelineService.assemble(TimelineFilter): merges curated events
(TimelineEventRepository), derived life-events (assembleDerivedEvents()),
and archive letters (DocumentService) into a year-bucketed TimelineDTO.
WITHIN_BAND_ORDER Comparator tested standalone before assembly tests.
ArchUnit Rule 2 entry for ..timeline.. domain added in same commit.

Refs #777
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/src/main/java/org/raddatz/familienarchiv/timeline/TimelineDTO.java

@@ -0,0 +1,15 @@
+package org.raddatz.familienarchiv.timeline;
+
+import io.swagger.v3.oas.annotations.media.Schema;
+
+import java.util.List;
+
+/**
+ * Assembled timeline response. Year bands are sorted ascending (oldest first).
+ * Undated entries have no usable date or {@code UNKNOWN} precision.
+ */
+public record TimelineDTO(
+        @Schema(requiredMode = Schema.RequiredMode.REQUIRED) List<TimelineYearDTO> years,
+        @Schema(requiredMode = Schema.RequiredMode.REQUIRED) List<TimelineEntryDTO> undated
+) {
+}

backend/src/main/java/org/raddatz/familienarchiv/timeline/TimelineFilter.java

@@ -0,0 +1,16 @@
+package org.raddatz.familienarchiv.timeline;
+
+import java.util.UUID;
+
+/**
+ * Immutable filter bag for {@link TimelineService#assemble(TimelineFilter)}.
+ * All fields are nullable — null means "no constraint on this dimension".
+ */
+public record TimelineFilter(
+        UUID personId,
+        Integer generation,
+        EventType type,
+        Integer fromYear,
+        Integer toYear
+) {
+}

backend/src/main/java/org/raddatz/familienarchiv/timeline/TimelineService.java

@@ -0,0 +1,260 @@
+package org.raddatz.familienarchiv.timeline;
+
+import lombok.RequiredArgsConstructor;
+import lombok.extern.slf4j.Slf4j;
+
+import org.raddatz.familienarchiv.document.DatePrecision;
+import org.raddatz.familienarchiv.document.Document;
+import org.raddatz.familienarchiv.document.DocumentService;
+import org.raddatz.familienarchiv.exception.DomainException;
+import org.raddatz.familienarchiv.exception.ErrorCode;
+import org.raddatz.familienarchiv.person.Person;
+import org.raddatz.familienarchiv.person.PersonService;
+
+import org.springframework.stereotype.Service;
+
+import java.util.ArrayList;
+import java.util.Comparator;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.TreeMap;
+import java.util.UUID;
+import java.util.stream.Collectors;
+
+/**
+ * Assembles the family timeline from three sources — curated {@link TimelineEvent} rows,
+ * derived person life-events, and archive letters — into a year-bucketed {@link TimelineDTO}.
+ *
+ * <p>Cross-domain data is reached exclusively through domain services (PersonService,
+ * DocumentService). The only repository injected directly is {@link TimelineEventRepository}
+ * (same domain — constitution §1.3).
+ */
+@Service
+@RequiredArgsConstructor
+@Slf4j
+public class TimelineService {
+
+    /** Primary: precision rank descending (DAY first). Secondary: date ascending. Tertiary: title. Final: id. */
+    static final Comparator<TimelineEntryDTO> WITHIN_BAND_ORDER =
+            Comparator.comparingInt((TimelineEntryDTO e) -> precisionRank(e.precision())).reversed()
+                    .thenComparing(e -> e.eventDate() != null ? e.eventDate() : java.time.LocalDate.MAX)
+                    .thenComparing(e -> e.title() != null ? e.title() : "")
+                    .thenComparing(e -> {
+                        if (e.eventId() != null) return e.eventId().toString();
+                        if (e.documentId() != null) return e.documentId().toString();
+                        return "";
+                    });
+
+    private final TimelineEventRepository eventRepository;
+    private final TimelineEventService timelineEventService;
+    private final DocumentService documentService;
+    private final PersonService personService;
+
+    /**
+     * Assembles the timeline for the given filter. All filters are ANDed.
+     * Throws {@link DomainException} (bad request) when fromYear &gt; toYear.
+     * Throws {@link DomainException} (not found) when personId refers to an unknown person.
+     */
+    public TimelineDTO assemble(TimelineFilter filter) {
+        if (filter.fromYear() != null && filter.toYear() != null
+                && filter.fromYear() > filter.toYear()) {
+            throw DomainException.badRequest(ErrorCode.VALIDATION_ERROR,
+                    "toYear must not be before fromYear");
+        }
+
+        // Resolve generation person IDs once — used across all three layers
+        Set<UUID> genPersonIds = resolveGenerationPersonIds(filter.generation());
+
+        // ── curated events ───────────────────────────────────────────────────
+        List<TimelineEntryDTO> entries = new ArrayList<>();
+        for (TimelineEvent ev : eventRepository.findAll()) {
+            if (!passesTypeFilter(ev.getType(), filter.type())) continue;
+            if (!passesPersonFilter(ev.getPersons(), filter.personId())) continue;
+            if (!passesGenerationFilter(ev.getPersons(), genPersonIds)) continue;
+            if (!passesYearFilter(ev.getEventDate(), ev.getPrecision(), filter)) continue;
+            entries.add(mapEvent(ev));
+        }
+
+        // ── derived events ───────────────────────────────────────────────────
+        for (TimelineEntryDTO derived : timelineEventService.assembleDerivedEvents()) {
+            if (!passesTypeFilter(derived.type(), filter.type())) continue;
+            if (!passesDerivedPersonFilter(derived.linkedPersonIds(), filter.personId())) continue;
+            if (!passesDerivedGenerationFilter(derived.linkedPersonIds(), genPersonIds)) continue;
+            if (!passesYearFilter(derived.eventDate(), derived.precision(), filter)) continue;
+            entries.add(derived);
+        }
+
+        // ── letters ─────────────────────────────────────────────────────────
+        List<Document> docs = fetchDocuments(filter.personId());
+        for (Document doc : docs) {
+            if (!passesLetterGenerationFilter(doc, genPersonIds)) continue;
+            if (!passesYearFilter(doc.getDocumentDate(), doc.getMetaDatePrecision(), filter)) continue;
+            entries.add(mapDocument(doc));
+        }
+
+        return bucket(entries);
+    }
+
+    // ─── Bucketing ───────────────────────────────────────────────────────────
+
+    Map<Integer, List<TimelineEntryDTO>> bucketByYear(List<TimelineEntryDTO> entries) {
+        Map<Integer, List<TimelineEntryDTO>> map = new TreeMap<>();
+        for (TimelineEntryDTO e : entries) {
+            if (e.eventDate() == null || e.precision() == DatePrecision.UNKNOWN) continue;
+            map.computeIfAbsent(e.eventDate().getYear(), k -> new ArrayList<>()).add(e);
+        }
+        return map;
+    }
+
+    private TimelineDTO bucket(List<TimelineEntryDTO> entries) {
+        List<TimelineEntryDTO> undated = entries.stream()
+                .filter(e -> e.eventDate() == null || e.precision() == DatePrecision.UNKNOWN)
+                .sorted(WITHIN_BAND_ORDER)
+                .toList();
+
+        Map<Integer, List<TimelineEntryDTO>> byYear = bucketByYear(entries);
+        List<TimelineYearDTO> years = byYear.entrySet().stream()
+                .map(e -> new TimelineYearDTO(e.getKey(),
+                        e.getValue().stream().sorted(WITHIN_BAND_ORDER).toList()))
+                .toList();
+
+        return new TimelineDTO(years, undated);
+    }
+
+    // ─── Document fetch (global vs personId path) ────────────────────────────
+
+    private List<Document> fetchDocuments(UUID personId) {
+        if (personId == null) {
+            return documentService.getAllForTimeline();
+        }
+        // personId path: validate existence, then union sender+receiver (dedup by id)
+        personService.getById(personId);
+        Map<UUID, Document> seen = new LinkedHashMap<>();
+        for (Document d : documentService.getDocumentsBySender(personId)) seen.put(d.getId(), d);
+        for (Document d : documentService.getDocumentsByReceiver(personId)) seen.putIfAbsent(d.getId(), d);
+        return new ArrayList<>(seen.values());
+    }
+
+    // ─── Filter predicates ───────────────────────────────────────────────────
+
+    private boolean passesTypeFilter(EventType entryType, EventType filterType) {
+        return filterType == null || filterType == entryType;
+    }
+
+    private boolean passesYearFilter(java.time.LocalDate date, DatePrecision precision, TimelineFilter filter) {
+        if (date == null || precision == DatePrecision.UNKNOWN) return true; // undated → always passes
+        int year = date.getYear();
+        if (filter.fromYear() != null && year < filter.fromYear()) return false;
+        if (filter.toYear() != null && year > filter.toYear()) return false;
+        return true;
+    }
+
+    private boolean passesPersonFilter(Set<Person> persons, UUID personId) {
+        if (personId == null) return true;
+        return persons != null && persons.stream().anyMatch(p -> personId.equals(p.getId()));
+    }
+
+    private boolean passesDerivedPersonFilter(List<UUID> linkedIds, UUID personId) {
+        if (personId == null) return true;
+        return linkedIds != null && linkedIds.contains(personId);
+    }
+
+    private Set<UUID> resolveGenerationPersonIds(Integer generation) {
+        if (generation == null) return null;
+        return personService.getPersonsByGeneration(generation).stream()
+                .map(Person::getId)
+                .collect(Collectors.toSet());
+    }
+
+    private boolean passesGenerationFilter(Set<Person> persons, Set<UUID> genPersonIds) {
+        if (genPersonIds == null) return true;
+        if (persons == null || persons.isEmpty()) return false;
+        return persons.stream().anyMatch(p -> genPersonIds.contains(p.getId()));
+    }
+
+    private boolean passesDerivedGenerationFilter(List<UUID> linkedIds, Set<UUID> genPersonIds) {
+        if (genPersonIds == null) return true;
+        if (linkedIds == null || linkedIds.isEmpty()) return false;
+        return linkedIds.stream().anyMatch(genPersonIds::contains);
+    }
+
+    private boolean passesLetterGenerationFilter(Document doc, Set<UUID> genPersonIds) {
+        if (genPersonIds == null) return true;
+        Person sender = doc.getSender();
+        if (sender != null && genPersonIds.contains(sender.getId())) return true;
+        Set<Person> receivers = doc.getReceivers();
+        if (receivers != null) {
+            return receivers.stream().anyMatch(r -> genPersonIds.contains(r.getId()));
+        }
+        return false;
+    }
+
+    // ─── Mapping ─────────────────────────────────────────────────────────────
+
+    private TimelineEntryDTO mapEvent(TimelineEvent ev) {
+        List<UUID> personIds = ev.getPersons() == null ? List.of()
+                : ev.getPersons().stream().map(Person::getId).toList();
+        return new TimelineEntryDTO(
+                Kind.EVENT,
+                ev.getPrecision(),
+                false,
+                "",
+                "",
+                ev.getEventDate(),
+                ev.getEventDateEnd(),
+                ev.getTitle(),
+                ev.getType(),
+                ev.getId(),
+                null,
+                personIds,
+                null
+        );
+    }
+
+    private TimelineEntryDTO mapDocument(Document doc) {
+        return new TimelineEntryDTO(
+                Kind.LETTER,
+                doc.getMetaDatePrecision(),
+                false,
+                resolveSenderName(doc),
+                resolveReceiverName(doc),
+                doc.getDocumentDate(),
+                null,
+                doc.getTitle(),
+                null,
+                null,
+                doc.getId(),
+                List.of(),
+                null
+        );
+    }
+
+    private String resolveSenderName(Document doc) {
+        if (doc.getSender() != null) return doc.getSender().getDisplayName();
+        String text = doc.getSenderText();
+        return (text != null && !text.isBlank()) ? text : "";
+    }
+
+    private String resolveReceiverName(Document doc) {
+        Set<Person> receivers = doc.getReceivers();
+        if (receivers != null && !receivers.isEmpty()) {
+            return receivers.stream().findFirst().map(Person::getDisplayName).orElse("");
+        }
+        String text = doc.getReceiverText();
+        return (text != null && !text.isBlank()) ? text : "";
+    }
+
+    private static int precisionRank(DatePrecision precision) {
+        if (precision == null) return 0;
+        return switch (precision) {
+            case DAY -> 5;
+            case MONTH -> 4;
+            case SEASON -> 3;
+            case YEAR -> 2;
+            case APPROX -> 1;
+            default -> 0;
+        };
+    }
+}

backend/src/main/java/org/raddatz/familienarchiv/timeline/TimelineYearDTO.java

@@ -0,0 +1,12 @@
+package org.raddatz.familienarchiv.timeline;
+
+import io.swagger.v3.oas.annotations.media.Schema;
+
+import java.util.List;
+
+/** One year's worth of timeline entries, sorted by {@link TimelineService#WITHIN_BAND_ORDER}. */
+public record TimelineYearDTO(
+        @Schema(requiredMode = Schema.RequiredMode.REQUIRED) int year,
+        @Schema(requiredMode = Schema.RequiredMode.REQUIRED) List<TimelineEntryDTO> entries
+) {
+}

backend/src/test/java/org/raddatz/familienarchiv/shared/ArchitectureTest.java

@@ -100,6 +100,13 @@ class ArchitectureTest {
             .and().resideInAPackage("..audit..")
             .should().dependOnClassesThat(foreignJpaRepositoryFor("audit"));
 
+    @ArchTest
+    static final ArchRule services_only_access_own_domain_repositories_timeline =
+        noClasses()
+            .that().areAnnotatedWith(Service.class)
+            .and().resideInAPackage("..timeline..")
+            .should().dependOnClassesThat(foreignJpaRepositoryFor("timeline"));
+
     // Rule 3: Infrastructure @Configuration classes must not end up scattered in domain packages.
     // Keeps cross-cutting setup (security, async, DB, storage) in dedicated packages
     // where it can be audited and reasoned about independently.

backend/src/test/java/org/raddatz/familienarchiv/timeline/TimelineServiceTest.java

@@ -0,0 +1,452 @@
+package org.raddatz.familienarchiv.timeline;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.mockito.InjectMocks;
+import org.mockito.Mock;
+import org.mockito.junit.jupiter.MockitoExtension;
+import org.raddatz.familienarchiv.document.DatePrecision;
+import org.raddatz.familienarchiv.document.Document;
+import org.raddatz.familienarchiv.document.DocumentService;
+import org.raddatz.familienarchiv.exception.DomainException;
+import org.raddatz.familienarchiv.person.Person;
+import org.raddatz.familienarchiv.person.PersonService;
+
+import java.time.LocalDate;
+import java.util.List;
+import java.util.Set;
+import java.util.UUID;
+
+import static org.assertj.core.api.Assertions.*;
+import static org.mockito.Mockito.*;
+
+@ExtendWith(MockitoExtension.class)
+class TimelineServiceTest {
+
+    @Mock TimelineEventRepository eventRepository;
+    @Mock TimelineEventService timelineEventService;
+    @Mock DocumentService documentService;
+    @Mock PersonService personService;
+
+    @InjectMocks TimelineService timelineService;
+
+    // ─── WITHIN_BAND_ORDER standalone tests (REQ-002) ────────────────────────
+
+    @Test
+    void within_band_order_day_precision_sorts_before_year() {
+        var dayEntry = letter(LocalDate.of(1914, 7, 28), DatePrecision.DAY, "B-brief");
+        var yearEntry = letter(LocalDate.of(1914, 1, 1), DatePrecision.YEAR, "A-brief");
+
+        var sorted = List.of(yearEntry, dayEntry).stream()
+                .sorted(TimelineService.WITHIN_BAND_ORDER)
+                .toList();
+
+        assertThat(sorted).containsExactly(dayEntry, yearEntry);
+    }
+
+    @Test
+    void within_band_order_same_precision_and_date_sorts_alphabetically() {
+        var entryZ = letter(LocalDate.of(1914, 7, 28), DatePrecision.DAY, "Zimmer");
+        var entryA = letter(LocalDate.of(1914, 7, 28), DatePrecision.DAY, "Adler");
+
+        var sorted = List.of(entryZ, entryA).stream()
+                .sorted(TimelineService.WITHIN_BAND_ORDER)
+                .toList();
+
+        assertThat(sorted).containsExactly(entryA, entryZ);
+    }
+
+    @Test
+    void within_band_order_same_title_uses_document_id_as_tiebreak() {
+        UUID id1 = UUID.fromString("00000000-0000-0000-0000-000000000001");
+        UUID id2 = UUID.fromString("00000000-0000-0000-0000-000000000002");
+        var e1 = new TimelineEntryDTO(Kind.LETTER, DatePrecision.DAY, false, "", "",
+                LocalDate.of(1914, 7, 28), null, "Same Title", null, null, id1, List.of(), null);
+        var e2 = new TimelineEntryDTO(Kind.LETTER, DatePrecision.DAY, false, "", "",
+                LocalDate.of(1914, 7, 28), null, "Same Title", null, null, id2, List.of(), null);
+
+        var sorted = List.of(e2, e1).stream()
+                .sorted(TimelineService.WITHIN_BAND_ORDER)
+                .toList();
+
+        assertThat(sorted.get(0).documentId()).isEqualTo(id1);
+    }
+
+    // ─── Assembly tests (issue-spec order) ──────────────────────────────────
+
+    @Test
+    void test1_empty_archive_returns_empty_dto() {
+        // REQ-013, REQ-007
+        when(eventRepository.findAll()).thenReturn(List.of());
+        when(timelineEventService.assembleDerivedEvents()).thenReturn(List.of());
+        when(documentService.getAllForTimeline()).thenReturn(List.of());
+
+        TimelineDTO result = timelineService.assemble(noFilters());
+
+        assertThat(result.years()).isEmpty();
+        assertThat(result.undated()).isEmpty();
+    }
+
+    @Test
+    void test2_one_year_letter_returns_one_year_band() {
+        // REQ-007
+        var doc = docWithDate(LocalDate.of(1914, 1, 1), DatePrecision.YEAR);
+        when(eventRepository.findAll()).thenReturn(List.of());
+        when(timelineEventService.assembleDerivedEvents()).thenReturn(List.of());
+        when(documentService.getAllForTimeline()).thenReturn(List.of(doc));
+
+        TimelineDTO result = timelineService.assemble(noFilters());
+
+        assertThat(result.years()).hasSize(1);
+        assertThat(result.years().get(0).year()).isEqualTo(1914);
+        assertThat(result.years().get(0).entries()).hasSize(1);
+        assertThat(result.years().get(0).entries().get(0).kind()).isEqualTo(Kind.LETTER);
+        assertThat(result.undated()).isEmpty();
+    }
+
+    @Test
+    void test3a_null_date_letter_goes_to_undated() {
+        // REQ-003
+        var doc = Document.builder().id(UUID.randomUUID()).title("Brief")
+                .metaDatePrecision(DatePrecision.YEAR).build(); // documentDate stays null
+        when(eventRepository.findAll()).thenReturn(List.of());
+        when(timelineEventService.assembleDerivedEvents()).thenReturn(List.of());
+        when(documentService.getAllForTimeline()).thenReturn(List.of(doc));
+
+        TimelineDTO result = timelineService.assemble(noFilters());
+
+        assertThat(result.years()).isEmpty();
+        assertThat(result.undated()).hasSize(1);
+    }
+
+    @Test
+    void test3b_unknown_precision_letter_goes_to_undated() {
+        // REQ-003
+        var doc = docWithDate(LocalDate.of(1914, 1, 1), DatePrecision.UNKNOWN);
+        when(eventRepository.findAll()).thenReturn(List.of());
+        when(timelineEventService.assembleDerivedEvents()).thenReturn(List.of());
+        when(documentService.getAllForTimeline()).thenReturn(List.of(doc));
+
+        TimelineDTO result = timelineService.assemble(noFilters());
+
+        assertThat(result.years()).isEmpty();
+        assertThat(result.undated()).hasSize(1);
+    }
+
+    @Test
+    void test4_letter_with_null_sender_and_null_senderText_produces_empty_names() {
+        // REQ-005
+        var doc = Document.builder().id(UUID.randomUUID()).title("Brief")
+                .metaDatePrecision(DatePrecision.YEAR)
+                .documentDate(LocalDate.of(1914, 1, 1))
+                .build(); // no sender, no senderText, no receivers, no receiverText
+        when(eventRepository.findAll()).thenReturn(List.of());
+        when(timelineEventService.assembleDerivedEvents()).thenReturn(List.of());
+        when(documentService.getAllForTimeline()).thenReturn(List.of(doc));
+
+        TimelineDTO result = timelineService.assemble(noFilters());
+
+        var entry = result.years().get(0).entries().get(0);
+        assertThat(entry.senderName()).isEqualTo("");
+        assertThat(entry.receiverName()).isEqualTo("");
+    }
+
+    @Test
+    void test5_day_precision_sorts_before_year_in_same_year_band() {
+        // REQ-002
+        var dayLetter = docWithDate(LocalDate.of(1914, 7, 28), DatePrecision.DAY, "B-brief");
+        var yearLetter = docWithDate(LocalDate.of(1914, 1, 1), DatePrecision.YEAR, "A-brief");
+        when(eventRepository.findAll()).thenReturn(List.of());
+        when(timelineEventService.assembleDerivedEvents()).thenReturn(List.of());
+        when(documentService.getAllForTimeline()).thenReturn(List.of(yearLetter, dayLetter));
+
+        TimelineDTO result = timelineService.assemble(noFilters());
+
+        var entries = result.years().get(0).entries();
+        assertThat(entries).hasSize(2);
+        assertThat(entries.get(0).precision()).isEqualTo(DatePrecision.DAY);
+        assertThat(entries.get(1).precision()).isEqualTo(DatePrecision.YEAR);
+    }
+
+    @Test
+    void test6_same_precision_same_date_sorted_alphabetically_by_title() {
+        // REQ-002
+        var letterZ = docWithDate(LocalDate.of(1914, 7, 28), DatePrecision.DAY, "Zimmer");
+        var letterA = docWithDate(LocalDate.of(1914, 7, 28), DatePrecision.DAY, "Adler");
+        when(eventRepository.findAll()).thenReturn(List.of());
+        when(timelineEventService.assembleDerivedEvents()).thenReturn(List.of());
+        when(documentService.getAllForTimeline()).thenReturn(List.of(letterZ, letterA));
+
+        TimelineDTO result = timelineService.assemble(noFilters());
+
+        var entries = result.years().get(0).entries();
+        assertThat(entries).hasSize(2);
+        assertThat(entries.get(0).title()).isEqualTo("Adler");
+        assertThat(entries.get(1).title()).isEqualTo("Zimmer");
+    }
+
+    @Test
+    void test7a_range_event_placed_only_in_start_year_band() {
+        // REQ-004
+        var rangeEvent = event("WW1", EventType.HISTORICAL,
+                LocalDate.of(1914, 7, 28), DatePrecision.RANGE, LocalDate.of(1918, 11, 11));
+        when(eventRepository.findAll()).thenReturn(List.of(rangeEvent));
+        when(timelineEventService.assembleDerivedEvents()).thenReturn(List.of());
+        when(documentService.getAllForTimeline()).thenReturn(List.of());
+
+        TimelineDTO result = timelineService.assemble(noFilters());
+
+        assertThat(result.years()).hasSize(1);
+        assertThat(result.years().get(0).year()).isEqualTo(1914);
+        assertThat(result.years().stream().noneMatch(y -> y.year() == 1918)).isTrue();
+    }
+
+    @Test
+    void test7b_range_event_with_null_eventDateEnd_does_not_crash() {
+        // REQ-004
+        var rangeEvent = event("Offener Zeitraum", EventType.PERSONAL,
+                LocalDate.of(1914, 1, 1), DatePrecision.RANGE, null);
+        when(eventRepository.findAll()).thenReturn(List.of(rangeEvent));
+        when(timelineEventService.assembleDerivedEvents()).thenReturn(List.of());
+        when(documentService.getAllForTimeline()).thenReturn(List.of());
+
+        assertThatCode(() -> timelineService.assemble(noFilters())).doesNotThrowAnyException();
+    }
+
+    @Test
+    void test8_range_event_excluded_when_start_year_before_fromYear() {
+        // REQ-004
+        var rangeEvent = event("WW1", EventType.HISTORICAL,
+                LocalDate.of(1914, 7, 28), DatePrecision.RANGE, LocalDate.of(1918, 11, 11));
+        when(eventRepository.findAll()).thenReturn(List.of(rangeEvent));
+        when(timelineEventService.assembleDerivedEvents()).thenReturn(List.of());
+        when(documentService.getAllForTimeline()).thenReturn(List.of());
+
+        // fromYear=1915 → start year 1914 is outside → excluded
+        TimelineDTO result = timelineService.assemble(new TimelineFilter(null, null, null, 1915, null));
+
+        assertThat(result.years()).isEmpty();
+    }
+
+    @Test
+    void test9a_type_filter_does_not_exclude_letters_but_excludes_wrong_type_events() {
+        // REQ-009
+        var doc = docWithDate(LocalDate.of(1914, 1, 1), DatePrecision.YEAR, "Brief");
+        var historicalEvent = event("Sarajevo", EventType.HISTORICAL,
+                LocalDate.of(1914, 6, 28), DatePrecision.DAY, null);
+        var personalEvent = event("Geburt", EventType.PERSONAL,
+                LocalDate.of(1914, 8, 1), DatePrecision.DAY, null);
+        when(eventRepository.findAll()).thenReturn(List.of(historicalEvent, personalEvent));
+        when(timelineEventService.assembleDerivedEvents()).thenReturn(List.of());
+        when(documentService.getAllForTimeline()).thenReturn(List.of(doc));
+
+        // filter: only HISTORICAL events
+        TimelineDTO result = timelineService.assemble(new TimelineFilter(null, null, EventType.HISTORICAL, null, null));
+
+        long letters = result.years().stream().flatMap(y -> y.entries().stream())
+                .filter(e -> e.kind() == Kind.LETTER).count();
+        long personalEvents = result.years().stream().flatMap(y -> y.entries().stream())
+                .filter(e -> e.kind() == Kind.EVENT && e.type() == EventType.PERSONAL).count();
+        assertThat(letters).isEqualTo(1);
+        assertThat(personalEvents).isEqualTo(0);
+    }
+
+    @Test
+    void test9b_generation_filter_includes_letter_when_sender_matches_generation() {
+        // REQ-010
+        var sender = Person.builder().id(UUID.randomUUID())
+                .lastName("Mustermann").firstName("Max").generation(2).build();
+        var included = Document.builder().id(UUID.randomUUID()).title("Treffer")
+                .metaDatePrecision(DatePrecision.YEAR).documentDate(LocalDate.of(1914, 1, 1))
+                .sender(sender).build();
+        var excluded = docWithDate(LocalDate.of(1914, 1, 1), DatePrecision.YEAR, "Kein Treffer"); // no sender
+        when(eventRepository.findAll()).thenReturn(List.of());
+        when(timelineEventService.assembleDerivedEvents()).thenReturn(List.of());
+        when(documentService.getAllForTimeline()).thenReturn(List.of(included, excluded));
+        when(personService.getPersonsByGeneration(2)).thenReturn(List.of(sender));
+
+        TimelineDTO result = timelineService.assemble(new TimelineFilter(null, 2, null, null, null));
+
+        assertThat(result.years()).hasSize(1);
+        assertThat(result.years().get(0).entries()).hasSize(1);
+        assertThat(result.years().get(0).entries().get(0).title()).isEqualTo("Treffer");
+    }
+
+    @Test
+    void test9c_fromYear_toYear_inclusive_single_year_window() {
+        // REQ-011
+        var before = docWithDate(LocalDate.of(1913, 12, 31), DatePrecision.YEAR, "Vorher");
+        var inYear = docWithDate(LocalDate.of(1914, 6, 1), DatePrecision.MONTH, "Im Jahr");
+        var after = docWithDate(LocalDate.of(1915, 1, 1), DatePrecision.YEAR, "Nachher");
+        when(eventRepository.findAll()).thenReturn(List.of());
+        when(timelineEventService.assembleDerivedEvents()).thenReturn(List.of());
+        when(documentService.getAllForTimeline()).thenReturn(List.of(before, inYear, after));
+
+        TimelineDTO result = timelineService.assemble(new TimelineFilter(null, null, null, 1914, 1914));
+
+        assertThat(result.years()).hasSize(1);
+        assertThat(result.years().get(0).year()).isEqualTo(1914);
+        assertThat(result.years().get(0).entries().get(0).title()).isEqualTo("Im Jahr");
+    }
+
+    @Test
+    void test10_adversarial_and_logic_neither_event_passes_both_filters() {
+        // REQ-012 — type AND year must both pass
+        var wrongType = event("Personal", EventType.PERSONAL,
+                LocalDate.of(1914, 1, 1), DatePrecision.YEAR, null);
+        var wrongYear = event("Historical outside", EventType.HISTORICAL,
+                LocalDate.of(1920, 1, 1), DatePrecision.YEAR, null);
+        when(eventRepository.findAll()).thenReturn(List.of(wrongType, wrongYear));
+        when(timelineEventService.assembleDerivedEvents()).thenReturn(List.of());
+        when(documentService.getAllForTimeline()).thenReturn(List.of());
+
+        TimelineDTO result = timelineService.assemble(new TimelineFilter(null, null, EventType.HISTORICAL, 1914, 1914));
+
+        assertThat(result.years()).isEmpty();
+        assertThat(result.undated()).isEmpty();
+    }
+
+    @Test
+    void test11_personId_scoping_deduplicates_letter_appearing_as_sender_and_receiver() {
+        // REQ-008
+        UUID personId = UUID.randomUUID();
+        var person = Person.builder().id(personId).lastName("Mustermann").build();
+        var doc = Document.builder().id(UUID.randomUUID()).title("Brief")
+                .metaDatePrecision(DatePrecision.YEAR).documentDate(LocalDate.of(1914, 1, 1))
+                .sender(person)
+                .receivers(Set.of(person))
+                .build();
+        when(personService.getById(personId)).thenReturn(person);
+        when(eventRepository.findAll()).thenReturn(List.of());
+        when(timelineEventService.assembleDerivedEvents()).thenReturn(List.of());
+        when(documentService.getDocumentsBySender(personId)).thenReturn(List.of(doc));
+        when(documentService.getDocumentsByReceiver(personId)).thenReturn(List.of(doc));
+
+        TimelineDTO result = timelineService.assemble(new TimelineFilter(personId, null, null, null, null));
+
+        long total = result.years().stream().mapToLong(y -> y.entries().size()).sum()
+                + result.undated().size();
+        assertThat(total).isEqualTo(1);
+    }
+
+    @Test
+    void test12_personId_plus_generation_filter_returns_empty_when_generations_do_not_match() {
+        // REQ-012
+        UUID personId = UUID.randomUUID();
+        var person = Person.builder().id(personId).lastName("Mustermann").generation(1).build();
+        var doc = Document.builder().id(UUID.randomUUID()).title("Brief")
+                .metaDatePrecision(DatePrecision.YEAR).documentDate(LocalDate.of(1914, 1, 1))
+                .sender(person).build();
+        var gen2person = Person.builder().id(UUID.randomUUID()).lastName("Schmidt").generation(2).build();
+        when(personService.getById(personId)).thenReturn(person);
+        when(eventRepository.findAll()).thenReturn(List.of());
+        when(timelineEventService.assembleDerivedEvents()).thenReturn(List.of());
+        when(documentService.getDocumentsBySender(personId)).thenReturn(List.of(doc));
+        when(documentService.getDocumentsByReceiver(personId)).thenReturn(List.of());
+        when(personService.getPersonsByGeneration(2)).thenReturn(List.of(gen2person)); // person not in gen2
+
+        TimelineDTO result = timelineService.assemble(new TimelineFilter(personId, 2, null, null, null));
+
+        assertThat(result.years()).isEmpty();
+        assertThat(result.undated()).isEmpty();
+    }
+
+    @Test
+    void test13_null_generation_sender_not_returned_by_generation_filter() {
+        // REQ-020 — both sender and receiver have null generation → excluded
+        var nullGenSender = Person.builder().id(UUID.randomUUID()).lastName("Sender").build(); // generation = null
+        var doc = Document.builder().id(UUID.randomUUID()).title("Brief")
+                .metaDatePrecision(DatePrecision.YEAR).documentDate(LocalDate.of(1914, 1, 1))
+                .sender(nullGenSender).build();
+        when(eventRepository.findAll()).thenReturn(List.of());
+        when(timelineEventService.assembleDerivedEvents()).thenReturn(List.of());
+        when(documentService.getAllForTimeline()).thenReturn(List.of(doc));
+        when(personService.getPersonsByGeneration(1)).thenReturn(List.of()); // nobody in generation 1
+
+        TimelineDTO result = timelineService.assemble(new TimelineFilter(null, 1, null, null, null));
+
+        assertThat(result.years()).isEmpty();
+        assertThat(result.undated()).isEmpty();
+    }
+
+    @Test
+    void test14_year_band_contains_only_event_when_no_letters_in_that_year() {
+        var ev = event("Ausbruch", EventType.HISTORICAL, LocalDate.of(1914, 7, 28), DatePrecision.DAY, null);
+        when(eventRepository.findAll()).thenReturn(List.of(ev));
+        when(timelineEventService.assembleDerivedEvents()).thenReturn(List.of());
+        when(documentService.getAllForTimeline()).thenReturn(List.of());
+
+        TimelineDTO result = timelineService.assemble(noFilters());
+
+        assertThat(result.years()).hasSize(1);
+        assertThat(result.years().get(0).entries()).hasSize(1);
+        assertThat(result.years().get(0).entries().get(0).kind()).isEqualTo(Kind.EVENT);
+    }
+
+    @Test
+    void test15_range_event_start_year_equal_to_fromYear_is_included() {
+        // REQ-004 — inclusive lower bound
+        var rangeEvent = event("WW1", EventType.HISTORICAL,
+                LocalDate.of(1914, 7, 28), DatePrecision.RANGE, LocalDate.of(1918, 11, 11));
+        when(eventRepository.findAll()).thenReturn(List.of(rangeEvent));
+        when(timelineEventService.assembleDerivedEvents()).thenReturn(List.of());
+        when(documentService.getAllForTimeline()).thenReturn(List.of());
+
+        TimelineDTO result = timelineService.assemble(new TimelineFilter(null, null, null, 1914, null));
+
+        assertThat(result.years()).hasSize(1);
+        assertThat(result.years().get(0).year()).isEqualTo(1914);
+    }
+
+    @Test
+    void test16_fromYear_without_toYear_returns_all_items_from_that_year_onwards() {
+        // REQ-011
+        var old = docWithDate(LocalDate.of(1919, 12, 31), DatePrecision.YEAR, "Alt");
+        var first = docWithDate(LocalDate.of(1920, 1, 1), DatePrecision.YEAR, "Erst");
+        var newer = docWithDate(LocalDate.of(1921, 6, 1), DatePrecision.YEAR, "Newer");
+        when(eventRepository.findAll()).thenReturn(List.of());
+        when(timelineEventService.assembleDerivedEvents()).thenReturn(List.of());
+        when(documentService.getAllForTimeline()).thenReturn(List.of(old, first, newer));
+
+        TimelineDTO result = timelineService.assemble(new TimelineFilter(null, null, null, 1920, null));
+
+        assertThat(result.years()).hasSize(2);
+        assertThat(result.years().stream().noneMatch(y -> y.year() == 1919)).isTrue();
+    }
+
+    @Test
+    void fromYear_greater_than_toYear_throws_bad_request() {
+        // REQ-016 (service-layer guard)
+        assertThatThrownBy(() -> timelineService.assemble(new TimelineFilter(null, null, null, 1920, 1914)))
+                .isInstanceOf(DomainException.class);
+    }
+
+    // ─── Helpers ─────────────────────────────────────────────────────────────
+
+    private static TimelineFilter noFilters() {
+        return new TimelineFilter(null, null, null, null, null);
+    }
+
+    private static TimelineEntryDTO letter(LocalDate date, DatePrecision precision, String title) {
+        return new TimelineEntryDTO(Kind.LETTER, precision, false, "", "",
+                date, null, title, null, null, UUID.randomUUID(), List.of(), null);
+    }
+
+    private static Document docWithDate(LocalDate date, DatePrecision precision) {
+        return Document.builder().id(UUID.randomUUID()).title("Brief")
+                .metaDatePrecision(precision).documentDate(date).build();
+    }
+
+    private static Document docWithDate(LocalDate date, DatePrecision precision, String title) {
+        return Document.builder().id(UUID.randomUUID()).title(title)
+                .metaDatePrecision(precision).documentDate(date).build();
+    }
+
+    private static TimelineEvent event(String title, EventType type, LocalDate date,
+                                       DatePrecision precision, LocalDate endDate) {
+        return TimelineEvent.builder().id(UUID.randomUUID())
+                .title(title).type(type)
+                .eventDate(date).precision(precision).eventDateEnd(endDate)
+                .build();
+    }
+}