Answers the state of a batch, the errors by line it carries and rows: every row of the spreadsheet with its values, status (VALID, INVALID, ALREADY_EXISTS, REPEATED), errors and version. For a batch saved before the review existed, status and errors come from rowErrors and every version is 0.

A batch of another group answers 404, never 403, so a caller cannot tell a batch that exists elsewhere from one that does not exist.