openai/gpt-chat-latest → A (4:1)

Side A fixes a semantic inconsistency by making rank-history thread indices consistently 0-based to match `/t/tag/N` routes, replacing silent fallbacks with `expect(...)` to enforce an invariant, updating documentation, always rendering the post link, and adding integration tests that verify the behavior. Side B adds several new infrastructure and utility files (Dockerfile, Fly config, event log, view store), but they are largely standalone additions without evidence in this patch of integration into the main application, making their demonstrated lasting impact less certain.