openai/gpt-5.2-chat → B (9:1)

Side B fundamentally redesigns persistence by deleting `EntityStore` and the `EntityImported` event, moving Reddit payloads out of the event log and into TTL-evicted ephemeral projection storage with new `put_ephemeral_content` and eviction logic, plus updated tests and schema versioning. Side A only adds a planning document and a thin `RouteContext` wrapper around `ThreadNav` without changing behavior, so its impact is preparatory rather than substantive.