~x-ai/grok-latest → B (2:1)

B hardens core feed catch-up by anchoring on durable ingest index (not wall-clock ms), scanning the ordered ledger for explicit since, and enforcing per-viewer scope checks so concurrent same-ms posts and private-room grants/revokes neither drop updates nor leak; it ships FeedPost.room plus multi-user integration tests for those cases. A replaces a Reddit stub with a real broker/OAuth/rate-limit/parser path and browse hooks—valuable feature work—but B’s correctness and permission fixes are more foundational lasting product value.