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/tui/src/chatwidget.rs

@@ -1083,7 +1083,7 @@ impl ChatWidget {
                     self.on_user_message_event(ev);
                 }
             }
-            EventMsg::ConversationHistory(ev) => {
+            EventMsg::ConversationPath(ev) => {
                 self.app_event_tx
                     .send(crate::app_event::AppEvent::ConversationHistory(ev));
             }