openai/gpt-chat-latest → A (3:2)

Side A delivers concrete infrastructure improvements: it introduces a reusable `durable` RocksDB-backed storage crate, moves raw Reddit entity JSON out of the in-memory tree into an `EntityStore`, and replaces full event-log loading with line-by-line replay to reduce startup memory usage. Side B is a broad `CanonicalItemUrl` → `ItemId` refactor with routing and API updates that improves type structure, but it is primarily an internal representation change, whereas A directly adds durable storage and measurable runtime behavior improvements.