baba5e0replaced _advance_child with _advance(index, parent_buffer) driven from _hop; the two feed-order tests still patched the removed method. Patch _advance and record only index 2 (L1 hop feeding L2); assertions, expected order and the stale-feed negative control are unchanged. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> (cherry picked from commit3f47436073)