Function render_diff_preview 

pub fn render_diff_preview(
    file: FileDiff,
    width: u16,
    theme: &ReviewTheme,
    highlighter: &mut SyntaxHighlighter,
    options: DiffPreviewOptions,
) -> Vec<Line<'static>>

Renders one file without constructing review state or executing Git.

Hosts can call this for each replacement snapshot produced by FileDiff::from_texts; no watcher or incremental patch transport is needed.