feat(ui): add interactive spreadsheet component mo.ui.spreadsheet usi…

[RaphJean]

…ng FortuneSheet

## 📝 Summary                     
                                  
This PR integrates                

FortuneSheet (an open-source
React/TypeScript Excel-clone engine)
into the marimo notebook ecosystem
as an advanced, reactive UI widget:
mo.ui.spreadsheet.

It supports bidirectional syncing:
- **Backend → Frontend:**         

Serializes Pandas or Polars
DataFrames into memory-efficient CSV
URLs served by the kernel, along
with type metadata.
- Frontend → Backend:
Translates the edited sheet grid
into a row-oriented JSON array.
- Strict Data Integrity: Casts
cell values back to their original
dtypes (e.g., integers, floats,
dates, datetimes, booleans) on the
kernel before reconstructing the
DataFrame.

### Changes Made:                 
- **Backend (`marimo/`):**        
  - Created                       

marimo/_plugins/ui/_impl/spreadsheet. py implementing the spreadsheet
class extending UIElement.
- Registered spreadsheet in
the main marimo.ui package exports.
- Frontend (frontend/):
- Installed @fortune- sheet/react.
- Created SpreadsheetPlugin. tsx and workbook-wrapper.tsx
supporting:
- Lazy loading the workbook to
maintain fast initial page load
speeds.
- Dynamic headers mapping
DataFrame column names to Row 0 of
the sheet.
- Freezing the column headers
row (config.frozen.range.row_focus = 1).
- Explicit isLoading checks
to wait for async CSV data to finish
parsing before mounting FortuneSheet
(preventing empty sheets).
- Tests & Examples:
- Added a reactive smoke test
notebook at
marimo/_smoke_tests/spreadsheet_test. py.
- Added a detailed user example
notebook at examples/ui/spreadsheet. py showcasing real-time
recalculations of total items and
inventory values.

## 📋 Pre-Review Checklist        

- [ ] For large changes, or       

changes that affect the public API:
this change was discussed or
approved through an issue, on
[Discord](https://marimo.
io/discord?ref=pr), or the community
[discussions](https://github.
com/marimo-team/marimo/discussions)
(Please provide a link if
applicable).
- [x] Any AI generated code has
been reviewed line-by-line by the
human PR author, who stands by it.
- [ ] Video or media evidence is
provided for any visual changes
(optional).

## ✅ Merge Checklist             

- [x] I have read the [contributor

guidelines](https://github.
com/marimo-
team/marimo/blob/main/CONTRIBUTING.
md).
- [x] Documentation has been
updated where applicable, including
docstrings for API changes.
- [x] Tests have been added for
the changes made.

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Project	Deployment	Actions	Updated (UTC)
marimo-docs	Ready	Preview, Comment	Jun 27, 2026 8:39am

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