openai/gpt-chat-latest → A (9:1)

Side A implements a substantive authentication UX change: the server returns HTML fragments instead of redirects, the shared Poem JS fetch handler now morphs form innerHTML when a response contains HTML, auth templates are refactored to support fragment rendering, and matching CSS is added. Side B mainly corrects thread post indexing semantics by replacing a fallback with an invariant-enforcing expect, updating links, comments, and tests; while useful, it is a comparatively narrow consistency fix rather than a broader, reusable feature.