Function structural_symbol_diff 

pub fn structural_symbol_diff(
    old_source: &str,
    new_source: &str,
    extension: &str,
) -> Vec<StructuralSymbolDiff>

Compare two sources and report structural declaration changes for extension (e.g. "rs").

Identity is (symbol_name, start_line) within each version; body text inequality ⇒ Modified. Returns an empty list when tree-sitter is disabled or the language is unsupported.