csv-xlsx-import-export Weapon

Procedural arsenal for csv-xlsx-import-export-guardian. Encodes every decision the Guardian needs to make when helping a team add "upload your spreadsheet" to a React/Next.js product.

This weapon is deliberately opinionated: it picks winners from the research and explains the trade-offs rather than presenting false symmetry. When the research surfaces a gotcha (SheetJS cannot stream XLSX, ExcelJS WorkbookWriter has a memory leak), the guides encode the workaround, not the happy fiction.

When this weapon applies

Load when the Guardian is invoked on any of:

• "Build a CSV import feature"
• "Add XLSX file upload"
• "Column-mapping wizard for my importer"
• "Parse a 100MB spreadsheet without freezing the browser"
• "Export data to Excel with styled headers"
• "Is my CSV export safe from formula injection?"
• "Compare OneSchema vs Flatfile vs dromo vs hand-rolled"
• "Why is SheetJS not streaming my XLSX?"