openai/gpt-chat-latest → A (4:3)

Side A introduces a lasting routing and URL design change by adding canonical browse paths (`/~/...`), centralizing link generation with `ItemId::browse_href()`, parsing browse URLs, updating redirects, and adding integration/tests for the new navigation behavior. Although it also removes the theme feature and simplifies static asset handling, the new browse URL infrastructure affects routing and link consistency across the project, whereas Side B is primarily an internal storage refactor from deque to append-only list with query-time capping and corresponding cleanup/tests.