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/app_event.rs

@@ -1,4 +1,4 @@
-use codex_core::protocol::ConversationHistoryResponseEvent;
+use codex_core::protocol::ConversationPathResponseEvent;
 use codex_core::protocol::Event;
 use codex_file_search::FileMatch;
 
@@ -58,5 +58,5 @@ pub(crate) enum AppEvent {
     UpdateSandboxPolicy(SandboxPolicy),
 
     /// Forwarded conversation history snapshot from the current conversation.
-    ConversationHistory(ConversationHistoryResponseEvent),
+    ConversationHistory(ConversationPathResponseEvent),
 }