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

Side A fixes a real inconsistency (mixed 0/1-indexing between UI, RPC, and history rows), enforces an invariant with an explicit expect, and adds integration test assertions verifying the corrected index values, giving lasting correctness value. Side B is a smaller UI grouping refinement (splitting unranked siblings into separate groups) with a single unit test, useful but narrower in scope and impact.