Hoshe's finding: the H1 union-rejection mechanism correctly counts the new browse discriminator, but ambiguous_union_frame_is_rejected was carried over from PR #176 without a browse-inclusive case — a future demux/ShapeProbe refactor could drop the fifth shape from the union check with nothing to catch it. Adds browse+star_map and browse+city_names union frames, both asserting rejection. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>