test(document): close review-flagged coverage gaps for auto-title sync (#726)

- save-time: precision+raw carry-over when the DTO omits them (exercises the shared skip-null
  resolvers), and a RANGE label round-trip (Sara/Elicit)
- factory: a bare Document with a null index builds "" rather than NPE-ing (Felix)
- backfill matcher: negative near-misses — ASCII hyphen vs en dash, missing separator before
  trailing text, year-with-trailing-letters, index followed by text without a separator (Sara)
- backfill integration: tighten the count assertion to exactly 1 on the clean test DB (Sara)

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

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

@@ -371,6 +371,43 @@ class DocumentServiceTest {
         assertThat(stored.getTitle()).isEqualTo("C-0029 – Frühling 1943");
     }
 
+    @Test
+    void updateDocument_carriesStoredPrecisionAndRaw_whenDtoOmitsThem() throws Exception {
+        // Only the year changes; precision/end/raw are omitted from the DTO, so projectedState
+        // must carry them from the entity (exercises the skip-null effective* resolvers).
+        Document stored = makeStored("C-0029", LocalDate.of(1943, 4, 1), DatePrecision.SEASON, null);
+        stored.setMetaDateRaw("Frühling 1943");
+        stored.setTitle(documentTitleFactory.build(stored)); // "C-0029 – Frühling 1943"
+        DocumentUpdateDTO dto = editDto(stored.getTitle(), LocalDate.of(1944, 4, 1), null, null);
+
+        runUpdate(stored, dto);
+
+        assertThat(stored.getTitle()).isEqualTo("C-0029 – Frühling 1944");
+    }
+
+    @Test
+    void updateDocument_roundTripsRangeLabel_atSaveTime() throws Exception {
+        Document stored = Document.builder()
+                .id(UUID.randomUUID())
+                .originalFilename("C-0029")
+                .documentDate(LocalDate.of(1917, 1, 10))
+                .metaDatePrecision(DatePrecision.RANGE)
+                .metaDateEnd(LocalDate.of(1917, 1, 11))
+                .receivers(new HashSet<>())
+                .tags(new HashSet<>())
+                .build();
+        stored.setTitle(documentTitleFactory.build(stored)); // "C-0029 – 10.–11. Jan. 1917"
+        DocumentUpdateDTO dto = new DocumentUpdateDTO();
+        dto.setTitle(stored.getTitle());
+        dto.setDocumentDate(LocalDate.of(1918, 1, 10));
+        dto.setMetaDatePrecision(DatePrecision.RANGE);
+        dto.setMetaDateEnd(LocalDate.of(1918, 1, 11));
+
+        runUpdate(stored, dto);
+
+        assertThat(stored.getTitle()).isEqualTo("C-0029 – 10.–11. Jan. 1918");
+    }
+
     @Test
     void updateDocument_doesNotRegenerateToBlank_whenSubmittedTitleEmpty() throws Exception {
         Document stored = makeStored("C-0029", LocalDate.of(1928, 1, 1), DatePrecision.YEAR, "Berlin");

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

@@ -52,7 +52,7 @@ class DocumentTitleBackfillIntegrationTest {
 
         int count = documentService.backfillTitles();
 
-        assertThat(count).isGreaterThanOrEqualTo(1);
+        assertThat(count).isEqualTo(1); // exactly the one stale row seeded (clean test DB)
         assertThat(documentRepository.findById(stale.getId()).orElseThrow().getTitle())
                 .isEqualTo("C-0029 – 1928 – Berlin");
     }

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

@@ -118,6 +118,30 @@ class DocumentTitleBackfillMatcherTest {
         assertThat(overwritable("Ganz anderer Titel", null)).isFalse();
     }
 
+    // ─── near-miss: shapes that look almost machine-built but are not ──────────
+
+    @Test
+    void ascii_hyphen_instead_of_en_dash_separator_is_skipped() {
+        // The separator is " – " (en dash); a plain " - " is not the machine separator.
+        assertThat(overwritable("C-0029 - 1916", null)).isFalse();
+    }
+
+    @Test
+    void date_label_without_separator_before_trailing_text_is_skipped() {
+        // "1916 Berlin" is not a date label and is not joined by " – "; prose, not machine.
+        assertThat(overwritable("C-0029 – 1916 Berlin", null)).isFalse();
+    }
+
+    @Test
+    void year_with_trailing_letters_is_not_a_year_label() {
+        assertThat(overwritable("C-0029 – 1916er Brief", null)).isFalse();
+    }
+
+    @Test
+    void index_immediately_followed_by_text_without_separator_is_skipped() {
+        assertThat(overwritable("C-0029x – 1916", null)).isFalse();
+    }
+
     // ─── fail-closed guards ───────────────────────────────────────────────────
 
     @Test

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

@@ -71,6 +71,13 @@ class DocumentTitleFactoryTest {
         assertThat(factory.build(d)).isEqualTo("C-0029 – 1928");
     }
 
+    @Test
+    void bare_document_with_null_index_builds_empty_string_not_npe() {
+        // originalFilename is NOT NULL in production; the guard keeps a synthetic/partial entity
+        // from tripping StringBuilder(null) with an opaque NPE.
+        assertThat(factory.build(Document.builder().build())).isEqualTo("");
+    }
+
     @Test
     void day_precision_renders_the_full_german_label() {
         Document d = doc("C-0029")