openai/gpt-chat-latest → A (9:1)

Side A performs a substantial architectural refactor by splitting the forum code into focused modules (such as access, ingest, navigation, room members, and new-thread handling), while preserving behavior and introducing reusable helpers like ThreadNav and permission checks. It also adds a useful developer profiling script (`sample-fixture`) for diagnosing fixture processes, whereas Side B primarily removes the entire tree feature (`tree.rs`) and its exports, which is mostly feature deletion rather than an enduring improvement to the codebase.