MANDATORY DESIGN SYSTEM v2 (anti-slop)

Outputs from this skill must look designed, not generated. Default openpyxl styling (Calibri 11, visible gridlines, Sheet1 tabs, unformatted numbers) is a neon sign reading "an LLM made this". The design system below prevents that. This section supersedes any conflicting guidance below it.

The pipeline (use this, not raw openpyxl)

Build every xlsx through the builder API in build_xlsx.py. It auto-applies a theme, names the first sheet, hides gridlines, sets freeze panes + column widths, and registers NamedStyles so every cell you write is typographically on-brand.

from build_xlsx import (
    new_workbook, new_sheet, write_title_banner, write_section_header,
    write_table, write_total_row, write_kpi_band,
    write_note, write_source, set_column_widths, apply_freeze,
    save_and_validate, load_template,
)