Use thread rollback for Esc backtrack (#9140)

- Swap Esc backtrack to roll back the current thread instead of forking

codex-rs/tui2/src/app_event.rs

@@ -1,7 +1,6 @@
 use std::path::PathBuf;
 
 use codex_common::approval_presets::ApprovalPreset;
-use codex_core::protocol::ConversationPathResponseEvent;
 use codex_core::protocol::Event;
 use codex_core::protocol::RateLimitSnapshot;
 use codex_file_search::FileMatch;
@@ -180,9 +179,6 @@ pub(crate) enum AppEvent {
     /// Re-open the approval presets popup.
     OpenApprovalsPopup,
 
-    /// Forwarded conversation history snapshot from the current conversation.
-    ConversationHistory(ConversationPathResponseEvent),
-
     /// Open the branch picker option from the review popup.
     OpenReviewBranchPicker(PathBuf),