fix(dashboard): bulk-load document titles in getActivity to avoid N+1

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

backend/src/main/java/org/raddatz/familienarchiv/dashboard/DashboardService.java

@@ -124,12 +124,11 @@ public class DashboardService {
                 .toList();
 
         Map<UUID, String> titleCache = new HashMap<>();
-        for (UUID docId : docIds) {
-            try {
-                titleCache.put(docId, documentService.getDocumentById(docId).getTitle());
-            } catch (Exception e) {
-                titleCache.put(docId, "");
-            }
+        try {
+            documentService.getDocumentsByIds(docIds)
+                    .forEach(d -> titleCache.put(d.getId(), d.getTitle()));
+        } catch (Exception e) {
+            log.warn("Activity: failed to bulk-load document titles", e);
         }
 
         return rows.stream().map(row -> {

backend/src/main/java/org/raddatz/familienarchiv/service/DocumentService.java

@@ -484,6 +484,10 @@ public class DocumentService {
         return doc;
     }
 
+    public List<Document> getDocumentsByIds(List<UUID> ids) {
+        return documentRepository.findAllById(ids);
+    }
+
     public List<Document> getDocumentsWithoutVersions() {
         return documentRepository.findDocumentsWithoutVersions();
     }

backend/src/test/java/org/raddatz/familienarchiv/dashboard/DashboardServiceTest.java

@@ -12,13 +12,16 @@ import org.raddatz.familienarchiv.service.DocumentService;
 import org.raddatz.familienarchiv.service.TranscriptionService;
 import org.raddatz.familienarchiv.service.UserService;
 
-import java.time.LocalDateTime;
+import java.time.Instant;
 import java.util.HashSet;
 import java.util.List;
 import java.util.Optional;
 import java.util.UUID;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.ArgumentMatchers.anyList;
+import static org.mockito.Mockito.never;
+import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.when;
 
 @ExtendWith(MockitoExtension.class)
@@ -65,4 +68,40 @@ class DashboardServiceTest {
         assertThat(result.collaborators()).hasSize(1);
         assertThat(result.collaborators().get(0).name()).isEqualTo("Schmidt");
     }
+
+    // ─── getActivity bulk-load ────────────────────────────────────────────────
+
+    @Test
+    void getActivity_loadsDocumentTitles_withoutPerRowLookup() {
+        UUID userId = UUID.randomUUID();
+        UUID docId = UUID.randomUUID();
+
+        ActivityFeedRow row = mockFeedRow(docId, "ANNOTATION_CREATED");
+        when(auditLogQueryService.findActivityFeed(userId, 5)).thenReturn(List.of(row, row));
+
+        Document doc = Document.builder()
+                .id(docId).title("Familienbrief").originalFilename("f.pdf")
+                .receivers(new HashSet<>())
+                .build();
+        when(documentService.getDocumentsByIds(List.of(docId))).thenReturn(List.of(doc));
+
+        List<ActivityFeedItemDTO> items = dashboardService.getActivity(userId, 5);
+
+        assertThat(items).hasSize(2);
+        assertThat(items.get(0).documentTitle()).isEqualTo("Familienbrief");
+        verify(documentService, never()).getDocumentById(docId);
+    }
+
+    private ActivityFeedRow mockFeedRow(UUID docId, String kind) {
+        return new ActivityFeedRow() {
+            public String getKind() { return kind; }
+            public UUID getActorId() { return null; }
+            public String getActorInitials() { return ""; }
+            public String getActorColor() { return ""; }
+            public String getActorName() { return ""; }
+            public UUID getDocumentId() { return docId; }
+            public Instant getHappenedAt() { return Instant.now(); }
+            public boolean isYouMentioned() { return false; }
+        };
+    }
 }