Change forking to read the rollout from file (#3440)

This PR changes get history op to get path. Then, forking will use a
path. This will help us have one unified codepath for resuming/forking
conversations. Will also help in having rollout history in order. It
also fixes a bug where you won't see the UI when resuming after forking.

codex-rs/core/src/rollout/policy.rs

@@ -65,6 +65,6 @@ pub(crate) fn should_persist_event_msg(ev: &EventMsg) -> bool {
         | EventMsg::PlanUpdate(_)
         | EventMsg::TurnAborted(_)
         | EventMsg::ShutdownComplete
-        | EventMsg::ConversationHistory(_) => false,
+        | EventMsg::ConversationPath(_) => false,
     }
 }