openai/gpt-chat-latest → A (9:1)

Side A makes a substantial architectural change: it introduces a new RocksDB-backed `durable` workspace crate, moves raw Reddit entity JSON out of in-memory state into a persistent `EntityStore`, and replaces full event-log loading with streaming replay to reduce startup memory usage. Side B fixes a real correctness bug by removing shared browser sentinel delegates (changing browser sessions to use `Option<String>` delegates and adding integration tests), but its impact is much narrower than A's persistent storage and replay redesign.