Function should_bridge_aux_to_source 

pub fn should_bridge_aux_to_source(
    source_path: &str,
    aux_path: &str,
    source_count: usize,
    aux_count: usize,
) -> bool

Bridge test/fixture file to a source file with semantic token overlap. Guards: source/aux balance, role check, parent_dir difference, and token overlap (≥5 chars, non-generic).