Function fold_summary_text 

pub fn fold_summary_text(n: u32) -> String

The ⋯ N lines summary text trailing a collapsed head row, where n is folded_line_span’s count. One function so the TUI and GPUI peers cannot drift on spacing, glyph, or pluralisation — the TUI grew this as an inline format! and GPUI had no summary at all, which is exactly how two renderers end up disagreeing.

Callers paint it as trailing DECORATION: it sits outside the source column axis, so it must never widen the row’s wrap-segment count (see docs/dev/architecture/fold-architecture.md §5).