Discard opening prompts when side chat creation fails (#60558)

## Why

A failed side chat's opening prompt and image attachments could be restored into the parent chat's draft when dismissing the failure.

## What changed

Clear the pending opening message when sidebar chat creation fails, and stop restoring the opening message when side conversation creation returns an error.

## Testing

Update the sidebar chooser test to verify that dismissing a failed creation preserves the parent draft and a subsequent prompt without restoring the failed prompt or its image attachment.

GitOrigin-RevId: 1423786b2209e9441e0bc1504ffcf51e74ba7cde

codex-rs/tui/src/app/side.rs

@@ -884,6 +884,7 @@ impl App {
         };
         tui.frame_requester().schedule_frame();
         if let Err(message) = result {
+            pending.message = None;
             pending.state = sidebar::CreationState::Failed {
                 message,
                 cleanup: None,
@@ -1032,7 +1033,6 @@ impl App {
                 }
             }
             Err(err) => {
-                self.restore_side_user_message(user_message.take());
                 self.chat_widget
                     .set_side_conversation_context_label(/*label*/ None);
                 self.chat_widget.add_error_message(err);

codex-rs/tui/src/app/tests/key_chords.rs

@@ -1421,7 +1421,7 @@ async fn sidebar_chooser_preserves_the_parent_draft_and_starts_a_side_chat() ->
             request,
             started: std::time::Instant::now(),
         },
-        message: Some(first_prompt.clone()),
+        message: Some(first_prompt),
     });
     app.finish_side_creation(
         &mut tui,
@@ -1471,15 +1471,10 @@ prepared.
         super::side_frame(&mut app, &mut tui, ratatui::layout::Size::new(30, 8))?
             .contains("Open in sidebar")
     );
-    assert_eq!(
-        app.chat_widget.composer_draft_snapshot().remote_image_urls,
-        first_prompt.remote_image_urls
-    );
-    let draft = app.chat_widget.composer_text_with_pending();
-    assert!(
-        draft.contains("first prompt") && draft.contains("second prompt"),
-        "{draft}"
-    );
+    let draft = app.chat_widget.composer_draft_snapshot();
+    assert!(draft.remote_image_urls.is_empty());
+    insta::assert_snapshot!(draft.text, @"second prompt
+parent draft!");
     // A page fits a chat with a subtitle or two title-only chats.
     let pane = app.sidebar_mut();
     for _ in 0..4 {
@@ -1506,7 +1501,7 @@ prepared.
     }
     Box::pin(press(&mut app, &mut tui, &mut server, ctrl('c'))).await?;
     assert_eq!(app.chooser_focus(), None);
-    assert_eq!(app.chat_widget.composer_text_with_pending(), draft);
+    assert_eq!(app.chat_widget.composer_text_with_pending(), draft.text);
     tokio::time::resume();
     server.shutdown().await?;
     Ok(())