Branch conversations when editing earlier TUI prompts (#33201)

## What changed

- Fork the conversation immediately before the selected prompt instead of rolling back the current thread in place, preserving the original conversation.
- Reopen the selected prompt in the new conversation with its images, text elements, and mention bindings intact.
- Start a fresh conversation when editing the first prompt, show a dedicated continuation notice, and restore the prompt with an error if branching fails.

## Testing

- Cover branching before first and later prompts, source preservation, prompt restoration, hidden review prompts, mid-turn steering, in-progress turns, stale transcript entries, and mention bindings.

GitOrigin-RevId: 15473535b3f9733b0300711a498969e6d389db79

codex-rs/tui/src/chatwidget/tests/history_replay.rs

@@ -742,6 +742,28 @@ async fn forked_thread_history_line_without_name_shows_id_once_snapshot() {
     assert_chatwidget_snapshot!("forked_thread_history_line_without_name", combined);
 }
 
+#[tokio::test]
+async fn prompt_edit_thread_history_line_snapshot() {
+    let (mut chat, mut rx, _op_rx) = make_chatwidget_manual(/*model_override*/ None).await;
+
+    chat.emit_prompt_edit_thread_event();
+
+    let history_cell = tokio::time::timeout(std::time::Duration::from_secs(/*secs*/ 2), async {
+        loop {
+            match rx.recv().await {
+                Some(AppEvent::InsertHistoryCell(cell)) => break cell,
+                Some(_) => continue,
+                None => panic!("app event channel closed before prompt edit history was emitted"),
+            }
+        }
+    })
+    .await
+    .expect("timed out waiting for prompt edit history");
+    let combined = lines_to_single_string(&history_cell.display_lines(/*width*/ 80));
+
+    assert_chatwidget_snapshot!("prompt_edit_thread_history_line", combined);
+}
+
 #[tokio::test]
 async fn app_server_forked_thread_history_line_uses_app_server_title_snapshot() {
     let (chat, mut rx, _op_rx) = make_chatwidget_manual(/*model_override*/ None).await;

codex-rs/tui/src/chatwidget/tests/plan_mode.rs

@@ -1,6 +1,12 @@
 use super::*;
 use pretty_assertions::assert_eq;
 
+fn set_composer_text(chat: &mut ChatWidget, text: &str) {
+    chat.bottom_pane
+        .set_composer_text(text.to_string(), Vec::new(), Vec::new());
+    chat.refresh_plan_mode_nudge();
+}
+
 #[test]
 fn plan_mode_nudge_matches_only_standalone_plain_text_keyword() {
     assert!(contains_plan_keyword("plan"));
@@ -14,19 +20,19 @@ fn plan_mode_nudge_matches_only_standalone_plain_text_keyword() {
 #[tokio::test]
 async fn plan_mode_nudge_shows_only_for_eligible_default_mode_drafts() {
     let (mut chat, _rx, _op_rx) = make_chatwidget_manual(Some("gpt-5")).await;
-    chat.set_composer_text("make a plan".to_string(), Vec::new(), Vec::new());
+    set_composer_text(&mut chat, "make a plan");
     chat.pre_draw_tick();
     assert!(chat.bottom_pane.plan_mode_nudge_visible());
 
-    chat.set_composer_text("/plan".to_string(), Vec::new(), Vec::new());
+    set_composer_text(&mut chat, "/plan");
     chat.pre_draw_tick();
     assert!(!chat.bottom_pane.plan_mode_nudge_visible());
 
-    chat.set_composer_text("!plan".to_string(), Vec::new(), Vec::new());
+    set_composer_text(&mut chat, "!plan");
     chat.pre_draw_tick();
     assert!(!chat.bottom_pane.plan_mode_nudge_visible());
 
-    chat.set_composer_text("make a plan".to_string(), Vec::new(), Vec::new());
+    set_composer_text(&mut chat, "make a plan");
     let plan_mask = collaboration_modes::plan_mask(chat.model_catalog.as_ref())
         .expect("expected plan collaboration mode");
     chat.set_collaboration_mask(plan_mask);
@@ -37,7 +43,7 @@ async fn plan_mode_nudge_shows_only_for_eligible_default_mode_drafts() {
 #[tokio::test]
 async fn plan_mode_nudge_hides_while_task_or_modal_is_active() {
     let (mut chat, _rx, _op_rx) = make_chatwidget_manual(Some("gpt-5")).await;
-    chat.set_composer_text("make a plan".to_string(), Vec::new(), Vec::new());
+    set_composer_text(&mut chat, "make a plan");
     chat.pre_draw_tick();
     assert!(chat.bottom_pane.plan_mode_nudge_visible());
 
@@ -65,7 +71,7 @@ async fn plan_mode_nudge_dismissal_is_scoped_to_current_thread() {
     let first_thread = ThreadId::new();
     let second_thread = ThreadId::new();
     chat.thread_id = Some(first_thread);
-    chat.set_composer_text("make a plan".to_string(), Vec::new(), Vec::new());
+    set_composer_text(&mut chat, "make a plan");
     chat.pre_draw_tick();
     assert!(chat.bottom_pane.plan_mode_nudge_visible());
 
@@ -89,7 +95,7 @@ async fn plan_mode_nudge_dismissal_is_scoped_to_current_thread() {
 #[tokio::test]
 async fn plan_mode_nudge_shift_tab_uses_existing_mode_cycle_path() {
     let (mut chat, _rx, _op_rx) = make_chatwidget_manual(Some("gpt-5")).await;
-    chat.set_composer_text("make a plan".to_string(), Vec::new(), Vec::new());
+    set_composer_text(&mut chat, "make a plan");
     chat.pre_draw_tick();
     assert!(chat.bottom_pane.plan_mode_nudge_visible());
 
@@ -105,7 +111,7 @@ async fn plan_mode_nudge_snapshot() {
     chat.set_token_info(Some(make_token_info(
         /*total_tokens*/ 50_000, /*context_window*/ 100_000,
     )));
-    chat.set_composer_text("make a plan".to_string(), Vec::new(), Vec::new());
+    set_composer_text(&mut chat, "make a plan");
     chat.pre_draw_tick();
 
     assert_chatwidget_snapshot!("plan_mode_nudge", render_bottom_popup(&chat, /*width*/ 80));
@@ -114,7 +120,7 @@ async fn plan_mode_nudge_snapshot() {
 #[tokio::test]
 async fn plan_mode_nudge_narrow_snapshot() {
     let (mut chat, _rx, _op_rx) = make_chatwidget_manual(Some("gpt-5")).await;
-    chat.set_composer_text("make a plan".to_string(), Vec::new(), Vec::new());
+    set_composer_text(&mut chat, "make a plan");
     chat.pre_draw_tick();
 
     assert_chatwidget_snapshot!(