openai/gpt-chat-latest → A (9:1)

Side A consolidates the browser posting flow behind a single `POST /ui` RPC endpoint, introduces `resolve_web_session` to resolve username and bearer once, removes the duplicated `web_post.rs` handlers, updates forms, routes, and tests, and preserves functionality while simplifying the architecture. Side B is a narrow cleanup that removes unused parameters and an unnecessary preview update from `vote_compare_post_success_js`, improving maintainability but with much smaller project-wide impact.