Function extract_changes 

pub fn extract_changes(
    changes: &[FileChange],
) -> (Vec<ChangedSymbol>, Vec<String>)

Extract the symbols each file change touched, plus the set of content-changed files car-ast could not parse. A file with no content delta is ignored. A file with a content delta whose present side fails to parse is recorded in unparsed_changed_files (symbol checks are blind to it — only build/test covers it).