Function build_global_doc_diff_report 

pub fn build_global_doc_diff_report(
    repo: &Repository,
    docs_prefix: &str,
    limit: usize,
    with_blocks: bool,
) -> Result<Option<DocDiffReport>, DiffError>

Build the global build-history report across all docs under docs_prefix (repo-relative, e.g. "docs"). Each timeline point is a commit carrying every doc file it changed — the analogue of the original global /docs/diff report. Returns Ok(None) when no commit touched the docs. With with_blocks, each file additionally carries its rendered block diff.