Local worker foundation

CSV, XLS, and XLSX files are parsed in a browser Web Worker. The main interface receives typed progress and result messages, while source bytes and repaired rows remain on the device.

Downloads are created from the local result. The source file is never overwritten.

The free tier validates and exports a deterministic 100-row preview. The interface distinguishes preview counts from full-file counts, preserves access to the original, and identifies proposed paid access without implying that unprocessed rows were checked or can already be unlocked.

Column-mapping templates are stored in IndexedDB, scoped to the browser profile, and can be applied to later files without syncing spreadsheet headers or values to a server.