~x-ai/grok-latest → A (12:1)

A lands the structural ItemId type (replacing CanonicalItemUrl), splits wire normalization, and migrates reducer/ranking/RPC/HTML/tests so identity is typed end-to-end—lasting core design. B only drops a 1-based/fallback thread_post_index path to a strict 0-based index with tests/docs, a small correctness polish relative to A.