openai/gpt-chat-latest → B (3:2)

Side B removes a redundant early return in `GroupState::apply_vote`, allowing items and voted pairs to be registered while still relying on existing zero-weight edge handling, and updates tests to verify the intended behavior. Side A mainly adds a long planning document plus a thin `RouteContext` wrapper around `ThreadNav` and exports it, which is useful scaffolding but introduces little functional change on its own.