Brand the export header band and freeze the header row 🟥

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

infrastructure/xlsx/branding.py

@@ -0,0 +1,27 @@
+"""Monday.com-style branding for the Scenario Export workbook (ADR-0065).
+
+A programmatic openpyxl styling pass (no template): a bold indigo header band
+with white text, a frozen header row, subtle alternating row bands, and roomy
+column widths. The palette lives here as the single home for brand colour — the
+"no brand-colour constants anywhere" gap the review flagged.
+
+TODO(brand): swap the placeholder Monday-style hex for the real Domna brand
+palette once design supplies it.
+"""
+
+from __future__ import annotations
+
+from openpyxl.worksheet.worksheet import Worksheet
+
+# openpyxl colours are 8-char ARGB. Placeholder Monday-style palette.
+HEADER_FILL: str = "FF6C6CFF"  # indigo header band
+HEADER_FONT: str = "FFFFFFFF"  # white header text
+ROW_BAND_FILL: str = "FFF1F1FF"  # subtle alternating-row tint
+
+_COLUMN_WIDTH: int = 18
+
+
+def style_sheet(worksheet: Worksheet) -> None:
+    """Paint the Monday-style branding onto a populated worksheet: header band +
+    font, frozen header row, banded rows, and column widths."""
+    raise NotImplementedError

tests/infrastructure/xlsx/test_scenario_export_workbook.py

@@ -8,6 +8,7 @@ from io import BytesIO
 from openpyxl import load_workbook
 
 from domain.scenario_export.scenario_sheet import ExportSheet
+from infrastructure.xlsx.branding import HEADER_FILL
 from infrastructure.xlsx.scenario_export_workbook import render_workbook
 
 
@@ -48,3 +49,22 @@ def test_sanitises_and_deduplicates_scenario_sheet_names() -> None:
     assert len(set(names)) == 3
     assert all(len(name) <= 31 for name in names)
     assert not any(ch in name for name in names for ch in r":/\?*[]")
+
+
+def test_brands_the_header_row_and_freezes_it() -> None:
+    # arrange
+    sheet = ExportSheet(
+        columns=("property_id", "loft_insulation"),
+        rows=({"property_id": 1, "loft_insulation": 1200.0},),
+    )
+
+    # act
+    data = render_workbook([("Fabric first", sheet)])
+
+    # assert — the header is a bold, brand-filled band and the header row is
+    # frozen so it stays visible while scrolling.
+    worksheet = load_workbook(BytesIO(data))["Fabric first"]
+    header_cell = worksheet["A1"]
+    assert header_cell.font.bold is True
+    assert header_cell.fill.fgColor.rgb == HEADER_FILL
+    assert worksheet.freeze_panes == "A2"