openai/gpt-chat-latest → B (9:1)

Side B introduces substantive, lasting functionality: GitHub OAuth/session support, pseudonym claiming, new identity-related event types and projection logic, durable session storage, routing, UI integration, and accompanying tests. Side A mainly adds a detailed migration plan document plus a small `RouteContext` wrapper module and re-export, which is useful for future work but does not materially change project behavior.