I'd love to see Lumo able to work directly with Excel files — not just reading them, but actually editing them and returning the result as a downloadable .xlsx file.

My typical use case: I upload a spreadsheet and want Lumo to clean up data, recalculate columns, merge sheets, apply formulas, or reformat cells. Right now, the best I can get back is a markdown table or CSV text that I have to manually copy back into Excel — which is tedious and loses formatting, multiple sheets, and formulas.

It would be a huge productivity boost if Lumo could:

Read and analyze .xlsx files (including multiple sheets and formulas)
Apply requested changes (editing, filtering, calculations, restructuring)
Return the modified file as a proper .xlsx download — preserving original formatting where possible
Since privacy is Proton's core promise, this would also be a great differentiator: processing sensitive spreadsheets locally in an encrypted environment instead of uploading them to Big Tech AI tools that train on user data.