Pass 2 selected the merge winner from the union of both normalized-label
groups, so never-compared same-label/cross-file nodes could be pulled
into the union, bypassing the #1046/#1178 guards. Pick the winner from
[node, neighbor] only; group members that belong together still merge
via pass 1 (same file) or their own verified comparison.
Co-authored-by: Cursor <cursoragent@cursor.com>