Embedded spreadsheets always come with one of two failure modes: heavyweight (AG Grid Enterprise pricing, license keys) or toy (no formulas, no clipboard, no multi-sheet). Fancy Sheets sits in the middle: a full workbook that an agent can drive.

SheetWorkbook is a multi-sheet, formula-aware, clipboard-friendly spreadsheet with CSV import/export. Controlled by a workbook value object; agents drive it through sheet_* MCP tools (set cell, append row, name range, etc.).

Build a workbook with createEmptyWorkbook(), hold it in state, render <SheetWorkbook value onChange>. For agent operability, register the sheets bridge — and for xlsx export, hand the workbook to Holy Sheet (the PHP writer).