fix(translate): apply Excel chart text setters (were silently dropped)

Chart <a:t> elements (title, axis labels, series names) were collected and
sent to the LLM, but the apply loop never invoked their setters. Reason:
the apply loop iterated only text_elements[:sheet_name_offset], which
excluded the chart-text positions (sheet names were inserted in the
middle, pushing chart texts past sheet_name_offset). The LLM correctly
returned French for "Revenue by Product" / "Quantity Trend" / "Order #"
but the result was thrown away.

Fix: include the chart-text slice [sheet_name_offset + N .. total_texts]
in the apply loop. Setters for sheet names are still None, so they are
naturally skipped.

Add test_excel_chart_text_applied.py (2 end-to-end tests) using a fixed
provider that pre-translates every known chart text; the test asserts
all chart <a:t> values in the output .xlsx come from the FR table, not
the original English source.

tests/test_excel_chart_text_applied.py

@@ -0,0 +1,111 @@
+"""Regression test for the bug where chart <a:t> text was never written back
+to the .xlsx after translation, even though the LLM had returned the
+correct French translation.
+
+Root cause: the apply loop only iterated text_elements[:sheet_name_offset]
+which excluded the chart-text positions (sheet names were added in the
+middle, pushing chart texts past sheet_name_offset).
+"""
+import sys
+import shutil
+from pathlib import Path
+
+sys.path.insert(0, str(Path(__file__).resolve().parents[1]))
+
+from lxml import etree
+from openpyxl import load_workbook
+import zipfile
+
+from translators.excel_translator import ExcelTranslator
+
+NS_A = "http://schemas.openxmlformats.org/drawingml/2006/main"
+NS_C = "http://schemas.openxmlformats.org/drawingml/2006/chart"
+
+# Force a known translation for every chart-relevant string.
+FR = {
+    "Monthly Sales Volume (Units)": "Volume de ventes mensuel (unites)",
+    "Month": "Mois",
+    "Quantity": "Quantite",
+    "Revenue by Product": "Chiffre d'affaires par produit",
+    "Quantity Trend": "Tendance des quantites",
+    "Order #": "Numero de commande",
+}
+
+
+class FixedProvider:
+    def translate_batch(self, *args, **kwargs):
+        if args and hasattr(args[0], 'text'):
+            return [type("R", (), {"translated_text": FR.get(req.text, req.text)})() for req in args[0]]
+        texts = args[0] if args else kwargs.get('texts', [])
+        return [FR.get(t, t) for t in texts]
+
+
+def _read_chart_a_t(xlsx_path: Path):
+    out = {}
+    with zipfile.ZipFile(xlsx_path, 'r') as zf:
+        for name in zf.namelist():
+            if name.startswith('xl/charts/') and name.endswith('.xml'):
+                xml = etree.fromstring(zf.read(name))
+                out[name] = [t.text for t in xml.iter(f'{{{NS_A}}}t') if t.text]
+    return out
+
+
+def test_chart_texts_get_applied_to_output(tmp_path):
+    src = Path(r'D:\dev1405\office_translator\sample_files\test_corpus\test_excel.xlsx')
+    dst = tmp_path / "out.xlsx"
+    shutil.copy(src, dst)
+
+    tr = ExcelTranslator()
+    tr.set_provider(FixedProvider())
+    tr.translate_file(
+        input_path=src,
+        output_path=dst,
+        target_language="fr",
+        source_language="en",
+        translate_images=False,
+    )
+
+    chart_texts = _read_chart_a_t(dst)
+    # All chart a:t elements should be translated, not still English.
+    for cf, texts in chart_texts.items():
+        for t in texts:
+            assert t in FR.values(), (
+                f"{cf} still has untranslated text: {t!r}. "
+                f"Expected one of: {list(FR.values())}"
+            )
+
+
+def test_chart_refs_also_rewritten(tmp_path):
+    """Sheet refs are rewritten as part of the same fix flow."""
+    src = Path(r'D:\dev1405\office_translator\sample_files\test_corpus\test_excel.xlsx')
+    dst = tmp_path / "out2.xlsx"
+    shutil.copy(src, dst)
+
+    tr = ExcelTranslator()
+    tr.set_provider(FixedProvider())
+    tr.translate_file(
+        input_path=src,
+        output_path=dst,
+        target_language="fr",
+        source_language="en",
+        translate_images=False,
+    )
+
+    # Sheet name 'Sales 2024' is not in FR so it should not be renamed.
+    # The chart refs should still point at 'Sales 2024' (no rename happened).
+    with zipfile.ZipFile(dst, 'r') as zf:
+        for name in zf.namelist():
+            if name.startswith('xl/charts/') and name.endswith('.xml'):
+                xml = etree.fromstring(zf.read(name))
+                refs = [f.text for f in xml.iter(f'{{{NS_C}}}f') if f.text]
+                # The chart refs should still be valid (no broken refs)
+                for r in refs:
+                    assert '!' in r, f"Invalid chart ref in {name}: {r!r}"
+
+
+if __name__ == "__main__":
+    import tempfile
+    with tempfile.TemporaryDirectory() as d:
+        test_chart_texts_get_applied_to_output(Path(d))
+        test_chart_refs_also_rewritten(Path(d))
+    print("chart text applied test passed.")

translators/excel_translator.py

@@ -264,11 +264,20 @@ class ExcelTranslator:
                                 }
                             )
 
-                # Apply cell translations
+                # Apply cell + chart translations. The structure of
+                # text_elements is:
+                #   [0 .. sheet_name_offset)                 -> cell/header/footer setters
+                #   [sheet_name_offset .. +N)                 -> sheet names (setter=None)
+                #   [sheet_name_offset + N .. total_texts)    -> chart setters
+                # The old code only iterated the first slice, silently skipping
+                # every chart setter. We now concatenate the two non-None slices.
+                _n_sheet_names = len(sheet_names_to_translate)
+                _chart_slice = text_elements[sheet_name_offset + _n_sheet_names:]
+                _chart_trans_slice = translated_texts[sheet_name_offset + _n_sheet_names:]
                 for i, ((original_text, setter), translated) in enumerate(
                     zip(
-                        text_elements[:sheet_name_offset],
-                        translated_texts[:sheet_name_offset],
+                        text_elements[:sheet_name_offset] + _chart_slice,
+                        translated_texts[:sheet_name_offset] + _chart_trans_slice,
                     )
                 ):
                     if translated is not None and setter is not None: