Function render 

pub fn render(
    commit_diffs: &[CommitDiff],
    full: bool,
    colors: bool,
    reverse: bool,
    scope: SquashableScope,
    term_width: Option<u16>,
) -> String

Render the fragmap matrix for all commit_diffs to a String.

commit_diffs contains all commits in display order (regular commits followed by any synthetic rows such as staged/unstaged changes). full controls whether identical cluster columns are deduplicated. colors selects ANSI color output (matching the original fragmap tool) versus plain Unicode output (suitable for tests and --no-color piping). reverse prints rows oldest-first (highest matrix index first). scope controls what the squashable connector indicator means. term_width is the terminal column count used to compute the title column width dynamically (matching the original fragmap tool’s layout algorithm). When None a fixed 26-character title width is used.