Function render_review_envelope_with_diff 

pub fn render_review_envelope_with_diff(
    command: &str,
    provider: Provider,
    issues: &[CiIssue],
    diff_index: Option<&DiffIndex>,
) -> ReviewEnvelopeOutput

Render path the print site uses. Exposed so unit tests can pass a hand-crafted DiffIndex without poking the process-wide SHARED_DIFF cache (which is OnceLock-bounded and not reentrant under cargo test’s parallel runner).