feat(document): reject RANGE with end before start (#678)

Add ErrorCode.INVALID_DATE_RANGE and a validateDateRange guard on
DocumentService.updateDocument, run right after applyDatePrecision so it
fires before any save (updateDocumentTags persists earlier in the method).
Mirrors the V69 chk_meta_date_end_after_start CHECK: end >= start with a
null start allowed, using isBefore so equal dates stay valid. Turns a user
date typo into a clean 400 instead of a 500 + Sentry alert.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

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

@@ -381,6 +381,7 @@ public class DocumentService {
         doc.setTitle(dto.getTitle());
         doc.setDocumentDate(dto.getDocumentDate());
         applyDatePrecision(doc, dto);
+        validateDateRange(doc); // guard before any save (updateDocumentTags below persists)
         doc.setLocation(dto.getLocation());
         doc.setTranscription(dto.getTranscription());
         doc.setSummary(dto.getSummary());
@@ -468,6 +469,25 @@ public class DocumentService {
         }
     }
 
+    /**
+     * Friendly guard for the two V69 date-range CHECK constraints, run before save so a
+     * user date typo returns a clean 400 INVALID_DATE_RANGE instead of falling through to
+     * the generic handler (HTTP 500 + Sentry + ERROR log). Validates the post-apply {@code doc}
+     * state, not the DTO, because precision/end may have been carried over from the stored row
+     * when the DTO field was null. The DB CHECK remains the backstop; this never weakens it.
+     */
+    private void validateDateRange(Document doc) {
+        // Mirrors chk_meta_date_end_after_start: end >= start, with null start allowed.
+        // Use isBefore (equal dates are valid) — never !isAfter, which would contradict the DB's >=.
+        if (doc.getMetaDatePrecision() == DatePrecision.RANGE
+                && doc.getDocumentDate() != null
+                && doc.getMetaDateEnd() != null
+                && doc.getMetaDateEnd().isBefore(doc.getDocumentDate())) {
+            throw DomainException.badRequest(ErrorCode.INVALID_DATE_RANGE,
+                    "meta_date_end must not be before meta_date");
+        }
+    }
+
     @Transactional
     public Document updateDocumentTags(UUID docId, List<String> tagNames) {
         Document doc = documentRepository.findById(docId)

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

@@ -26,6 +26,8 @@ public enum ErrorCode {
     FILE_UPLOAD_FAILED,
     /** The uploaded file's content type is not supported (PDF/JPEG/PNG/TIFF only). 400 */
     UNSUPPORTED_FILE_TYPE,
+    /** A RANGE date is invalid: meta_date_end is before meta_date, or an end date is set without RANGE precision. 400 */
+    INVALID_DATE_RANGE,
 
     // --- Users ---
     /** A user with the given ID or username does not exist. 404 */

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

@@ -20,6 +20,7 @@ import org.raddatz.familienarchiv.document.MatchOffset;
 import org.raddatz.familienarchiv.document.SearchMatchData;
 import org.raddatz.familienarchiv.tag.TagOperator;
 import org.raddatz.familienarchiv.exception.DomainException;
+import org.raddatz.familienarchiv.exception.ErrorCode;
 import org.raddatz.familienarchiv.document.Document;
 import org.raddatz.familienarchiv.document.DocumentStatus;
 import org.raddatz.familienarchiv.person.Person;
@@ -225,6 +226,36 @@ class DocumentServiceTest {
         assertThat(doc.getMetaDateRaw()).isEqualTo("Juni 1916");
     }
 
+    // ─── updateDocument date-range validation (#678) ──────────────────────────
+
+    /** Builds a stored doc ready for an updateDocument call (collections initialised). */
+    private static Document docForRangeUpdate(UUID id) {
+        return Document.builder().id(id).receivers(new HashSet<>()).tags(new HashSet<>()).build();
+    }
+
+    private static DocumentUpdateDTO rangeDto(LocalDate start, LocalDate end) {
+        DocumentUpdateDTO dto = new DocumentUpdateDTO();
+        dto.setDocumentDate(start);
+        dto.setMetaDatePrecision(DatePrecision.RANGE);
+        dto.setMetaDateEnd(end);
+        return dto;
+    }
+
+    @Test
+    void updateDocument_rejectsRange_whenEndBeforeStart() {
+        UUID id = UUID.randomUUID();
+        Document doc = docForRangeUpdate(id);
+        when(documentRepository.findById(id)).thenReturn(Optional.of(doc));
+
+        DocumentUpdateDTO dto = rangeDto(LocalDate.of(1917, 1, 11), LocalDate.of(1917, 1, 10));
+
+        assertThatThrownBy(() -> documentService.updateDocument(id, dto, null, null))
+                .isInstanceOf(DomainException.class)
+                .extracting(e -> ((DomainException) e).getCode())
+                .isEqualTo(ErrorCode.INVALID_DATE_RANGE);
+        verify(documentRepository, never()).save(any());
+    }
+
     // ─── deleteTagCascading ───────────────────────────────────────────────────
 
     @Test