[codex] Migrate thread turns list to thread store (#19280)

- migrate `thread/turns/list` to ThreadStore. Uses ThreadStore for most
data now but merges in the in-memory state from thread manager
- keep v2 `thread/list` pathless-store friendly by converting
`StoredThread` directly to API `Thread`
- add regression coverage for pathless store history/listing

codex-rs/core/src/thread_manager.rs

@@ -52,7 +52,6 @@ use codex_protocol::protocol::TurnEnvironmentSelection;
 use codex_protocol::protocol::W3cTraceContext;
 use codex_rollout::RolloutConfig;
 use codex_state::DirectionalThreadSpawnEdgeStatus;
-#[cfg(debug_assertions)]
 use codex_thread_store::InMemoryThreadStore;
 use codex_thread_store::LocalThreadStore;
 use codex_thread_store::RemoteThreadStore;
@@ -268,7 +267,6 @@ pub fn thread_store_from_config(config: &Config) -> Arc<dyn ThreadStore> {
             Arc::new(LocalThreadStore::new(RolloutConfig::from_view(config)))
         }
         ThreadStoreConfig::Remote { endpoint } => Arc::new(RemoteThreadStore::new(endpoint)),
-        #[cfg(debug_assertions)]
         ThreadStoreConfig::InMemory { id } => InMemoryThreadStore::for_id(id),
     }
 }