~anthropic/claude-sonnet-latest → B (6:4)

Side B is a real, tested bugfix/behavior change: it changes sibling-group rendering so each unranked item forms its own group, backed by a new unit test verifying the exact grouping. Side A is purely a planning document plus a thin, unused wrapper struct (RouteContext) that duplicates existing ThreadNav methods without migrating any call sites, so it adds speculative scaffolding rather than shipped functionality.