openai/gpt-chat-latest → A (9:1)

Side A fixes core feed correctness by introducing a shared `rpc_feed` implementation that anchors implicit catch-up to durable ingest order instead of timestamps, enforces per-viewer visibility checks, includes room metadata, and adds extensive integration tests covering timestamp collisions, private-room permissions, and revoked access. Side B is primarily a code organization/refactoring change that splits forum code into new files and inlines some helper calls, with only a small auxiliary profiling script added; it does not materially change project behavior.