openai/gpt-chat-latest → A (25:1)

Side A makes a substantive behavioral fix by treating missing thread post indices as an invariant with `expect` instead of silently defaulting to 0, aligns rank-history indexing with the project's 0-based URL scheme, updates documentation, removes unnecessary conditional rendering, and adds integration tests verifying the new behavior. Side B is a minor UI text tweak that only removes a decorative separator before the view count.