Function display_text_or_default 

pub fn display_text_or_default(
    value: Option<String>,
    default: &str,
    field_name: &str,
    max_len: usize,
) -> String

Returns a normalized display string or a product default.

This helper is intended for runtime reads where invalid persisted values should not break public pages. It first strips control characters, then applies the same length and trimming rules as normalize_bounded_display_text.