Function scan_commit_body_within 

pub async fn scan_commit_body_within(
    cwd: &Path,
    sha: &str,
    budget: Duration,
) -> String

scan_commit_body with its command budget spelled; see the module’s scan_within.

The sha is resolved first, the same gate the commit scan’s own ref spec takes: it is a revision off a wire, and git show would read an option-shaped one as its own option. A sha that names no commit reads as no body.