openai/gpt-chat-latest → A (4:1)

Side A fixes the thread post index semantics by making rank history consistently use the 0-based URL index, replacing silent `unwrap_or(0)` fallbacks with `expect(...)` to catch broken invariants, updating documentation, removing conditional rendering, and adding integration tests that verify the behavior. Side B is primarily a large refactor of the URL canonicalization subsystem (moving logic into new graph/parse modules and deleting the old engine) but the shown patch mostly rewires interfaces and removes in-file tests without exposing the new implementation, making its lasting functional value less evident from the diff.