Function build_personal_folders 

fn build_personal_folders(
    names: Vec<String>,
    target: Option<(FolderId, &str)>,
) -> (Vec<FolderView>, usize)

Builds the folder views to import, plus the count of folders actually parsed from the source (excluding the injected target). When a target folder is given it becomes folder 0 and the imported groups are nested beneath it as "{target}/{group}" — the returned count is always names.len(), regardless of whether a target was given, so callers can’t accidentally report the merged list’s length (which includes the pre-existing target) as an import count.