Function read_query 

pub async fn read_query(
    query_fn: impl Future<Output = Result<Value, AppError>>,
    sql_query: &str,
    database_name: &str,
    validate: impl FnOnce(&str) -> Result<(), AppError>,
) -> Result<String, ErrorData>

Executes a read_query tool call with read-only validation.

The validate closure performs backend-specific SQL validation (e.g. read-only enforcement with the appropriate SQL dialect).

Errors

Returns ErrorData if validation, the backend query, or JSON serialization fails.