openai/gpt-chat-latest → B (3:2)

Side B refactors feed generation into a shared `rpc_feed` path and fixes a correctness bug by anchoring implicit catch-up to durable ingest order instead of timestamps, preventing missed posts during same-millisecond events or clock rollback while preserving permission checks. It also adds extensive multi-user integration tests covering private-room visibility and revoked access, whereas Side A primarily hardens authentication (fail-closed voting, Secure cookies, redirect sanitization, mock OAuth gating) and adds UI/account polish.