~x-ai/grok-latest → B (2:5)

B removes proven dead code in apply_vote and corrects the related test to match real behavior (items/pairs register; zero-weight edges stay absent), a small lasting simplification of production logic. A mostly adds a handoff plan.md plus a thin RouteContext newtype that still delegates to ThreadNav/CanonicalItemUrl—useful staging, but little durable design landed compared with B’s precise reducer cleanup.