Agent session history moves to cold storage after 7 days

Seven days after an agent session ends, its log moves from Runtime's database to cold storage, encrypted with a key for that session alone, and is verified before the database copy is deleted. Reads return the same events with the same paging through the API, the SDKs, the CLI, MCP and the console. History is billed as before, by its size. A read that cold storage cannot answer returns 503 history_unavailable and can be retried.