Function aggregate_content_hash 

pub fn aggregate_content_hash(documents: &[RenderedDocument]) -> String

Computes the aggregate content hash of a rendered document set: the SHA-256 hex digest over the sorted (tree_path, body hash) pairs. The aggregate identifies the exact reviewable content of a change — any body edit, addition, removal, or rename of a rendered document changes the value — so review verdicts bind it. Sorting makes the digest independent of enumeration order; a NUL separates path from hash and a newline terminates each pair so adjacent fields cannot alias across pair boundaries.