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_backtrack.rs

@@ -1,9 +1,11 @@
+use std::path::PathBuf;
+
 use crate::app::App;
 use crate::backtrack_helpers;
 use crate::pager_overlay::Overlay;
 use crate::tui;
 use crate::tui::TuiEvent;
-use codex_core::protocol::ConversationHistoryResponseEvent;
+use codex_core::protocol::ConversationPathResponseEvent;
 use codex_protocol::mcp_protocol::ConversationId;
 use color_eyre::eyre::Result;
 use crossterm::event::KeyCode;
@@ -98,7 +100,7 @@ impl App {
     ) {
         self.backtrack.pending = Some((base_id, drop_last_messages, prefill));
         self.app_event_tx.send(crate::app_event::AppEvent::CodexOp(
-            codex_core::protocol::Op::GetHistory,
+            codex_core::protocol::Op::GetPath,
         ));
     }
 
@@ -265,7 +267,7 @@ impl App {
     pub(crate) async fn on_conversation_history_for_backtrack(
         &mut self,
         tui: &mut tui::Tui,
-        ev: ConversationHistoryResponseEvent,
+        ev: ConversationPathResponseEvent,
     ) -> Result<()> {
         if let Some((base_id, _, _)) = self.backtrack.pending.as_ref()
             && ev.conversation_id == *base_id
@@ -281,14 +283,14 @@ impl App {
     async fn fork_and_switch_to_new_conversation(
         &mut self,
         tui: &mut tui::Tui,
-        ev: ConversationHistoryResponseEvent,
+        ev: ConversationPathResponseEvent,
         drop_count: usize,
         prefill: String,
     ) {
         let cfg = self.chat_widget.config_ref().clone();
         // Perform the fork via a thin wrapper for clarity/testability.
         let result = self
-            .perform_fork(ev.entries.clone(), drop_count, cfg.clone())
+            .perform_fork(ev.path.clone(), drop_count, cfg.clone())
             .await;
         match result {
             Ok(new_conv) => {
@@ -301,13 +303,11 @@ impl App {
     /// Thin wrapper around ConversationManager::fork_conversation.
     async fn perform_fork(
         &self,
-        entries: Vec<codex_protocol::models::ResponseItem>,
+        path: PathBuf,
         drop_count: usize,
         cfg: codex_core::config::Config,
     ) -> codex_core::error::Result<codex_core::NewConversation> {
-        self.server
-            .fork_conversation(entries, drop_count, cfg)
-            .await
+        self.server.fork_conversation(drop_count, cfg, path).await
     }
 
     /// Install a forked conversation into the ChatWidget and update UI to reflect selection.

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),
 }

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));
             }