Fix: merge cell-wrap continuation rows in vocabulary extraction

When textbook authors wrap text within a cell (e.g. long German
translations), OCR treats each physical line as a separate row.
New _merge_wrapped_rows() detects this by checking if the primary
column (EN) is empty — indicating a continuation, not a new entry.

Handles: empty EN + DE text, empty EN + example text, parenthetical
continuations like "(bei)", triple wraps, comma-separated lists.

12 tests added covering all cases.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

klausur-service/backend/tests/test_merge_wrapped_rows.py

@@ -0,0 +1,135 @@
+"""Tests for _merge_wrapped_rows — cell-wrap continuation row merging."""
+
+import pytest
+import sys
+import os
+
+sys.path.insert(0, os.path.join(os.path.dirname(__file__), '..'))
+from cv_cell_grid import _merge_wrapped_rows
+
+
+def _entry(row_index, english='', german='', example=''):
+    return {
+        'row_index': row_index,
+        'english': english,
+        'german': german,
+        'example': example,
+    }
+
+
+class TestMergeWrappedRows:
+    """Test cell-wrap continuation row merging."""
+
+    def test_basic_en_empty_merge(self):
+        """EN empty, DE has text → merge DE into previous row."""
+        entries = [
+            _entry(0, english='take part (in)', german='teilnehmen (an), mitmachen', example='More than 200 singers took'),
+            _entry(1, english='', german='(bei)', example='part in the concert.'),
+        ]
+        result = _merge_wrapped_rows(entries)
+        assert len(result) == 1
+        assert result[0]['german'] == 'teilnehmen (an), mitmachen (bei)'
+        assert result[0]['example'] == 'More than 200 singers took part in the concert.'
+
+    def test_en_empty_de_only(self):
+        """EN empty, only DE continuation (no example)."""
+        entries = [
+            _entry(0, english='competition', german='der Wettbewerb,'),
+            _entry(1, english='', german='das Turnier'),
+        ]
+        result = _merge_wrapped_rows(entries)
+        assert len(result) == 1
+        assert result[0]['german'] == 'der Wettbewerb, das Turnier'
+
+    def test_en_empty_example_only(self):
+        """EN empty, only example continuation."""
+        entries = [
+            _entry(0, english='to arrive', german='ankommen', example='We arrived at the'),
+            _entry(1, english='', german='', example='hotel at midnight.'),
+        ]
+        result = _merge_wrapped_rows(entries)
+        assert len(result) == 1
+        assert result[0]['example'] == 'We arrived at the hotel at midnight.'
+
+    def test_de_empty_paren_continuation(self):
+        """DE empty, EN starts with parenthetical → merge into previous EN."""
+        entries = [
+            _entry(0, english='to take part', german='teilnehmen'),
+            _entry(1, english='(in)', german=''),
+        ]
+        result = _merge_wrapped_rows(entries)
+        assert len(result) == 1
+        assert result[0]['english'] == 'to take part (in)'
+
+    def test_de_empty_lowercase_continuation(self):
+        """DE empty, EN starts lowercase → merge into previous EN."""
+        entries = [
+            _entry(0, english='to put up', german='aufstellen'),
+            _entry(1, english='with sth.', german=''),
+        ]
+        result = _merge_wrapped_rows(entries)
+        assert len(result) == 1
+        assert result[0]['english'] == 'to put up with sth.'
+
+    def test_no_merge_both_have_content(self):
+        """Both EN and DE have text → normal row, don't merge."""
+        entries = [
+            _entry(0, english='house', german='Haus'),
+            _entry(1, english='garden', german='Garten'),
+        ]
+        result = _merge_wrapped_rows(entries)
+        assert len(result) == 2
+
+    def test_no_merge_new_word_uppercase(self):
+        """EN has uppercase text, DE is empty → could be a new word, not merged."""
+        entries = [
+            _entry(0, english='house', german='Haus'),
+            _entry(1, english='Garden', german=''),
+        ]
+        result = _merge_wrapped_rows(entries)
+        assert len(result) == 2
+
+    def test_triple_wrap(self):
+        """Three consecutive wrapped rows → all merge into first."""
+        entries = [
+            _entry(0, english='competition', german='der Wettbewerb,'),
+            _entry(1, english='', german='das Turnier,'),
+            _entry(2, english='', german='der Wettkampf'),
+        ]
+        result = _merge_wrapped_rows(entries)
+        assert len(result) == 1
+        assert result[0]['german'] == 'der Wettbewerb, das Turnier, der Wettkampf'
+
+    def test_empty_entries(self):
+        """Empty list."""
+        assert _merge_wrapped_rows([]) == []
+
+    def test_single_entry(self):
+        """Single entry unchanged."""
+        entries = [_entry(0, english='house', german='Haus')]
+        result = _merge_wrapped_rows(entries)
+        assert len(result) == 1
+
+    def test_mixed_normal_and_wrapped(self):
+        """Mix of normal rows and wrapped rows."""
+        entries = [
+            _entry(0, english='house', german='Haus'),
+            _entry(1, english='take part (in)', german='teilnehmen (an),'),
+            _entry(2, english='', german='mitmachen (bei)'),
+            _entry(3, english='garden', german='Garten'),
+        ]
+        result = _merge_wrapped_rows(entries)
+        assert len(result) == 3
+        assert result[0]['english'] == 'house'
+        assert result[1]['german'] == 'teilnehmen (an), mitmachen (bei)'
+        assert result[2]['english'] == 'garden'
+
+    def test_comma_separator_handling(self):
+        """Previous DE ends with comma → no extra space needed."""
+        entries = [
+            _entry(0, english='word', german='Wort,'),
+            _entry(1, english='', german='Ausdruck'),
+        ]
+        result = _merge_wrapped_rows(entries)
+        assert len(result) == 1
+        assert result[0]['german'] == 'Wort, Ausdruck'