fix(upload): structured error codes for quick-upload, fix duplicate filename crash

- Switch errors from plain strings to { filename, code } objects so the
  frontend can show translated messages instead of raw exception text
- Add UNSUPPORTED_FILE_TYPE error code end-to-end (Java enum → errors.ts
  → de/en/es messages)
- Fix IncorrectResultSizeDataAccessException when a filename exists more
  than once in the DB: use findFirstByOriginalFilename instead of
  findByOriginalFilename in storeDocument()

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

backend/src/main/java/org/raddatz/familienarchiv/controller/DocumentController.java

@@ -110,14 +110,15 @@ public class DocumentController {
     private static final Set<String> ALLOWED_CONTENT_TYPES = Set.of(
             "application/pdf", "image/jpeg", "image/png", "image/tiff");
 
-    public record QuickUploadResult(List<Document> created, List<String> errors) {}
+    public record UploadError(String filename, String code) {}
+    public record QuickUploadResult(List<Document> created, List<UploadError> errors) {}
 
     @PostMapping(value = "/quick-upload", consumes = MediaType.MULTIPART_FORM_DATA_VALUE)
     @RequirePermission(Permission.WRITE_ALL)
     public QuickUploadResult quickUpload(
             @RequestPart(value = "files", required = false) List<MultipartFile> files) {
         List<Document> created = new ArrayList<>();
-        List<String> errors = new ArrayList<>();
+        List<UploadError> errors = new ArrayList<>();
 
         if (files == null || files.isEmpty()) {
             return new QuickUploadResult(created, errors);
@@ -125,13 +126,13 @@ public class DocumentController {
 
         for (MultipartFile file : files) {
             if (!ALLOWED_CONTENT_TYPES.contains(file.getContentType())) {
-                errors.add(file.getOriginalFilename() + ": unsupported file type");
+                errors.add(new UploadError(file.getOriginalFilename(), "UNSUPPORTED_FILE_TYPE"));
                 continue;
             }
             try {
                 created.add(documentService.storeDocument(file));
             } catch (Exception e) {
-                errors.add(file.getOriginalFilename() + ": " + e.getMessage());
+                errors.add(new UploadError(file.getOriginalFilename(), "FILE_UPLOAD_FAILED"));
                 log.warn("Quick upload failed for file {}: {}", file.getOriginalFilename(), e.getMessage());
             }
         }

backend/src/main/java/org/raddatz/familienarchiv/exception/ErrorCode.java

@@ -17,6 +17,8 @@ public enum ErrorCode {
     FILE_NOT_FOUND,
     /** An error occurred while uploading a file to object storage. 500 */
     FILE_UPLOAD_FAILED,
+    /** The uploaded file's content type is not supported (PDF/JPEG/PNG/TIFF only). 400 */
+    UNSUPPORTED_FILE_TYPE,
 
     // --- Users ---
     /** A user with the given ID or username does not exist. 404 */

backend/src/main/java/org/raddatz/familienarchiv/repository/DocumentRepository.java

@@ -21,6 +21,9 @@ public interface DocumentRepository extends JpaRepository<Document, UUID>, JpaSp
     // Wichtig für den Abgleich beim Excel-Import & Datei-Upload
     Optional<Document> findByOriginalFilename(String originalFilename);
 
+    // Wie oben, gibt aber nur das erste Ergebnis zurück — sicher wenn doppelte Dateinamen existieren
+    Optional<Document> findFirstByOriginalFilename(String originalFilename);
+
     // Findet alle Dokumente mit einem bestimmten Status
     // z.B. um alle offenen "PLACEHOLDER" zu finden
     List<Document> findByStatus(DocumentStatus status);

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

@@ -52,8 +52,8 @@ public class DocumentService {
     public Document storeDocument(MultipartFile file) throws IOException {
         String originalFilename = file.getOriginalFilename();
 
-        // 1. Check for existing record
+        // 1. Check for existing record (findFirst to survive duplicate filenames in the DB)
-        Optional<Document> existingDoc = documentRepository.findByOriginalFilename(originalFilename);
+        Optional<Document> existingDoc = documentRepository.findFirstByOriginalFilename(originalFilename);
         Document document;
 
         if (existingDoc.isPresent()) {

backend/src/test/java/org/raddatz/familienarchiv/controller/DocumentControllerTest.java

@@ -23,7 +23,6 @@ import java.util.Collections;
 import java.util.List;
 import java.util.UUID;
 
-import static org.hamcrest.Matchers.containsString;
 import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.Mockito.when;
 import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
@@ -150,6 +149,7 @@ class DocumentControllerTest {
         mockMvc.perform(multipart("/api/documents/quick-upload").file(file))
                 .andExpect(status().isOk())
                 .andExpect(jsonPath("$.created[0].title").value("scan001"))
+                .andExpect(jsonPath("$.errors").isArray())
                 .andExpect(jsonPath("$.errors").isEmpty());
     }
 
@@ -163,7 +163,8 @@ class DocumentControllerTest {
         mockMvc.perform(multipart("/api/documents/quick-upload").file(file))
                 .andExpect(status().isOk())
                 .andExpect(jsonPath("$.created").isEmpty())
-                .andExpect(jsonPath("$.errors[0]").value(containsString("report.docx")));
+                .andExpect(jsonPath("$.errors[0].filename").value("report.docx"))
+                .andExpect(jsonPath("$.errors[0].code").value("UNSUPPORTED_FILE_TYPE"));
     }
 
     // ─── GET /api/documents/{id}/versions ────────────────────────────────────

backend/src/test/java/org/raddatz/familienarchiv/service/DocumentServiceTest.java

@@ -221,7 +221,7 @@ class DocumentServiceTest {
         FileService.UploadResult uploadResult = new FileService.UploadResult("documents/uuid_scan001.pdf", "abc123");
         Document saved = Document.builder().id(UUID.randomUUID()).title("scan001").originalFilename("scan001.pdf").build();
 
-        when(documentRepository.findByOriginalFilename("scan001.pdf")).thenReturn(Optional.empty());
+        when(documentRepository.findFirstByOriginalFilename("scan001.pdf")).thenReturn(Optional.empty());
         when(documentRepository.save(any())).thenReturn(saved);
         when(fileService.uploadFile(any(), any())).thenReturn(uploadResult);
 
@@ -241,7 +241,7 @@ class DocumentServiceTest {
                 .id(UUID.randomUUID()).title("Brief an Oma").originalFilename("scan001.pdf")
                 .status(org.raddatz.familienarchiv.model.DocumentStatus.PLACEHOLDER).build();
 
-        when(documentRepository.findByOriginalFilename("scan001.pdf")).thenReturn(Optional.of(placeholder));
+        when(documentRepository.findFirstByOriginalFilename("scan001.pdf")).thenReturn(Optional.of(placeholder));
         when(documentRepository.save(any())).thenReturn(placeholder);
         when(fileService.uploadFile(any(), any())).thenReturn(uploadResult);
 

frontend/messages/de.json

@@ -7,6 +7,7 @@
 	"error_document_no_file": "Diesem Dokument ist noch keine Datei zugeordnet.",
 	"error_file_not_found": "Die Datei konnte im Speicher nicht gefunden werden.",
 	"error_file_upload_failed": "Die Datei konnte nicht hochgeladen werden.",
+	"error_unsupported_file_type": "Dieses Dateiformat wird nicht unterstützt.",
 	"error_user_not_found": "Der Benutzer wurde nicht gefunden.",
 	"error_import_already_running": "Ein Import läuft bereits. Bitte warten Sie, bis dieser abgeschlossen ist.",
 	"error_unauthorized": "Sie sind nicht angemeldet.",

frontend/messages/en.json

@@ -7,6 +7,7 @@
 	"error_document_no_file": "No file is associated with this document.",
 	"error_file_not_found": "The file could not be found in storage.",
 	"error_file_upload_failed": "The file could not be uploaded.",
+	"error_unsupported_file_type": "This file format is not supported.",
 	"error_user_not_found": "User not found.",
 	"error_import_already_running": "An import is already running. Please wait for it to finish.",
 	"error_unauthorized": "You are not logged in.",

frontend/messages/es.json

@@ -7,6 +7,7 @@
 	"error_document_no_file": "No hay ningún archivo asociado a este documento.",
 	"error_file_not_found": "El archivo no pudo encontrarse en el almacenamiento.",
 	"error_file_upload_failed": "No se pudo subir el archivo.",
+	"error_unsupported_file_type": "Este formato de archivo no está admitido.",
 	"error_user_not_found": "Usuario no encontrado.",
 	"error_import_already_running": "Ya hay una importación en curso. Por favor, espere a que finalice.",
 	"error_unauthorized": "No ha iniciado sesión.",

frontend/src/lib/errors.ts

@@ -9,6 +9,7 @@ export type ErrorCode =
 	| 'DOCUMENT_NO_FILE'
 	| 'FILE_NOT_FOUND'
 	| 'FILE_UPLOAD_FAILED'
+	| 'UNSUPPORTED_FILE_TYPE'
 	| 'USER_NOT_FOUND'
 	| 'EMAIL_ALREADY_IN_USE'
 	| 'WRONG_CURRENT_PASSWORD'
@@ -54,6 +55,8 @@ export function getErrorMessage(code: ErrorCode | string | undefined): string {
 			return m.error_file_not_found();
 		case 'FILE_UPLOAD_FAILED':
 			return m.error_file_upload_failed();
+		case 'UNSUPPORTED_FILE_TYPE':
+			return m.error_unsupported_file_type();
 		case 'USER_NOT_FOUND':
 			return m.error_user_not_found();
 		case 'EMAIL_ALREADY_IN_USE':

frontend/src/routes/+page.svelte

@@ -7,6 +7,7 @@ import { untrack } from 'svelte';
 import { SvelteURLSearchParams } from 'svelte/reactivity';
 import { m } from '$lib/paraglide/messages.js';
 import { formatDate } from '$lib/utils/date';
+import { getErrorMessage } from '$lib/errors';
 
 let { data } = $props();
 
@@ -101,7 +102,10 @@ async function uploadFiles(files: File[]) {
 				messages.push({ text: m.upload_success({ count: result.created.length }), isError: false });
 			}
 			for (const err of result.errors ?? []) {
-				messages.push({ text: err, isError: true });
+				messages.push({
+					text: `${err.filename}: ${getErrorMessage(err.code)}`,
+					isError: true
+				});
 			}
 			await invalidateAll();
 		} else {