~x-ai/grok-latest → B (2:1)

B adds a focused regression test of core rank-centrality behavior (26-item spanning tree with perfect strength ratios recovers true order), which permanently guards product-critical ranking logic. A improves local DX (cargo-watch fixture, persistent fixture-data/, preferred port) and trims redundant room-page markup, but that is peripheral tooling rather than lasting correctness of the main system.