validate re-runs every row rule, checks conflicts and reports license headroom without writing anything; commit creates the rows that are ready. Any other value is 400.

1–200 row objects of {sheetRow?, extension, firstName, lastName, voicemailEmail, missedCallEmail}: the extension must be digits and unique within the file, firstName is required, a missing lastName is only a warning, and invalid email lists are errors. Numbers already used by an extension or a shared voicemail box are marked skip_exists rather than failing the import, and non-string values are read as empty strings.