Function between 

pub fn between(
    city_root: &Path,
    base: GitOid,
    head: Head,
) -> Result<Vec<FileChange>, StorageError>

What moved between base and head, one row per file, path order.

Path order rather than size order: a reader looking for one file finds it in the same place every time, and a list that reorders itself as the numbers change is a list nobody can scan twice.

Errors

Propagates whatever opening the repository, finding the commits, or walking the difference reports.