sheet-authoring

# Authoring an open-sheet workbook ## The one rule **Never write a cell address.** Not `B5`. Not `SUM(B2:B13)`. Not `$A$1`. The framework assigns every coordinate *after* it has laid the blocks out, and references resolve against that layout. Writing an address by hand means writing a number that is correct only until someone adds a row — and then it is silently wrong, which in a financial model is worse than broken. If you catch yourself counting rows to work out where something landed, stop. The thing you want is a reference. The single exception is `raw('...')`, the deliberate escape hatch — see [references/formulas.md](references/formulas.md). ## The file contract ```tsx // sheets/<id>/index.tsx import { Sheet, Table, Workbook, col, sub, type SheetMeta } from '@open-sheet/core' export const meta: SheetMeta = { title: 'FY26 Budget', // shown in the viewer and used as the export name description: 'One line.', // optional theme: 'corporate-neutral', // optional; links back to themes/<id>.md createdAt: '2026-08-18T00:00:00.000Z', } export const design: DesignSystem = { … } // optional; see the Design panel note export default ( <Workbook> <Sheet name="…">…</Sheet> </Workbook> ) ``` The default export must be a `<Workbook>` containing `<Sheet>` children. `meta` and `design` are plain object literals — the dev UI parses and rewrites them, and a spread or an imported value makes the workbook untweakable. ## Structure in JSX, data in TypeS...