Blank separator columns (E, U) carry no header fill 🟩

backend/magic_plan/tests/test_audit_script.py

@@ -302,3 +302,18 @@ def test_write_data_rows_places_door_data_at_cols_22_to_25() -> None:
     assert ws.cell(row=3, column=23).value == 762.0
     assert ws.cell(row=3, column=28).value is None
     assert ws.cell(row=3, column=29).value is None
+
+
+def test_write_headers_blank_separator_columns_have_no_fill() -> None:
+    # Arrange
+    wb = openpyxl.Workbook()
+    ws = wb.active  # type: ignore[assignment]
+
+    # Act
+    _write_headers(ws)
+
+    # Assert — cols 5 (E) and 21 (U) have no fill in either header row
+    for col in (5, 21):
+        for row in (1, 2):
+            fill = ws.cell(row=row, column=col).fill
+            assert fill.patternType is None, f"col {col} row {row} should have no fill"