Function export_records 

pub fn export_records(
    vault_root: &Path,
    requested_path: &Path,
    format: Format,
    records: &[Record],
    select: Option<&[String]>,
    link_index: Option<&LinkGraph>,
) -> Result<PathBuf>

Export a list of Records to a file under the vault root.

If select is Some(&[..]) and non-empty, those field names define the output columns; otherwise the column set is the union of all frontmatter keys across the records, always prefixed with _name. Virtual fields like _backlink_count are resolved via link_index when present.

Returns the actual absolute path written (after path resolution and any auto-suffix on filename collision).