Respect rendered width when adding TUI history (#38075)

## What changed

- Initialize new chat widgets with the current terminal width.
- Determine whether an added history cell is visible using the active history
  render mode and the width available after ambient-pet reservations.
- Saturate diff-summary width calculations so extremely narrow terminals remain
  renderable.

## Testing

- Cover width-sensitive history insertion with an ambient pet, raw-output mode,
  and a diff summary narrower than its indentation.

GitOrigin-RevId: 82d20900e0637431be7646b4f4aba61810ff74c1

codex-rs/tui/src/app.rs

@@ -1019,6 +1019,7 @@ impl App {
                 (ChatWidget::new_with_app_event(init), Some(forked))
             }
         };
+        chat_widget.note_rendered_width(tui.terminal.last_known_screen_size.width);
         chat_widget.remote_connection = remote_connection;
         let thread_and_widget_ms = thread_and_widget_started_at.elapsed().as_millis();
         chat_widget

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

@@ -533,6 +533,8 @@ impl App {
             /*initial_user_message*/ None,
         );
         self.replace_chat_widget(ChatWidget::new_with_app_event(init));
+        self.chat_widget
+            .note_rendered_width(tui.terminal.last_known_screen_size.width);
         if blocks_direct_input {
             self.chat_widget.set_parent_owned_thread();
         }
@@ -754,6 +756,8 @@ impl App {
             initial_user_message,
         );
         self.replace_chat_widget(ChatWidget::new_with_app_event(init));
+        self.chat_widget
+            .note_rendered_width(tui.terminal.last_known_screen_size.width);
         if started.blocks_direct_input {
             self.mark_primary_thread_parent_owned(started.session.thread_id);
         }

codex-rs/tui/src/chatwidget.rs

@@ -705,7 +705,7 @@ pub(crate) struct ChatWidget {
     quit_shortcut_key: Option<KeyBinding>,
     // Runtime metrics accumulated across delta snapshots for the active turn.
     turn_runtime_metrics: RuntimeMetricsSummary,
-    last_rendered_width: std::cell::Cell<Option<usize>>,
+    last_rendered_width: std::cell::Cell<Option<u16>>,
     // Feedback sink for /feedback
     feedback: codex_feedback::CodexFeedback,
     // Current session rollout path (if known)
@@ -1239,8 +1239,17 @@ impl ChatWidget {
                 .active_cell
                 .as_ref()
                 .is_some_and(|c| c.as_any().is::<history_cell::SessionHeaderHistoryCell>());
+        let history_width = self
+            .last_rendered_width
+            .get()
+            .map(|width| self.history_wrap_width(width))
+            .unwrap_or(u16::MAX);
 
-        if !keep_placeholder_header_active && !cell.display_lines(u16::MAX).is_empty() {
+        if !keep_placeholder_header_active
+            && !cell
+                .display_lines_for_mode(history_width, self.history_render_mode())
+                .is_empty()
+        {
             // Only break exec grouping if the cell renders visible lines.
             if !self.has_active_stream_tail() {
                 self.flush_active_cell();
@@ -1583,7 +1592,6 @@ impl ChatWidget {
             if width == 0 {
                 None
             } else {
-                let width = u16::try_from(width).unwrap_or(u16::MAX);
                 let width = usize::from(self.history_wrap_width(width));
                 Some(crate::width::usable_content_width(width, reserved_cols).unwrap_or(1))
             }
@@ -1643,7 +1651,7 @@ impl ChatWidget {
     /// rebuilding runs through app-level resize reflow.
     pub(crate) fn on_terminal_resize(&mut self, width: u16) {
         let had_rendered_width = self.last_rendered_width.get().is_some();
-        self.last_rendered_width.set(Some(width as usize));
+        self.last_rendered_width.set(Some(width));
         let stream_width = self.current_stream_width(/*reserved_cols*/ 2);
         let plan_stream_width = self.current_stream_width(/*reserved_cols*/ 4);
         if let Some(controller) = self.stream_controller.as_mut() {

codex-rs/tui/src/chatwidget/rendering.rs

@@ -58,7 +58,7 @@ impl ChatWidget {
     }
 
     pub(crate) fn note_rendered_width(&self, width: u16) {
-        self.last_rendered_width.set(Some(width as usize));
+        self.last_rendered_width.set(Some(width));
     }
 }
 

codex-rs/tui/src/chatwidget/settings_popups.rs

@@ -8,14 +8,10 @@ use super::*;
 impl ChatWidget {
     pub(super) fn open_theme_picker(&mut self) {
         let codex_home = codex_utils_home_dir::find_codex_home().ok();
-        let terminal_width = self
-            .last_rendered_width
-            .get()
-            .and_then(|width| u16::try_from(width).ok());
         let params = crate::theme_picker::build_theme_picker_params(
             self.config.tui_theme.as_deref(),
             codex_home.as_deref(),
-            terminal_width,
+            self.last_rendered_width.get(),
         );
         self.bottom_pane.show_selection_view(params);
     }

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

@@ -2409,6 +2409,61 @@ async fn ambient_pet_can_be_disabled() {
     assert!(chat.ambient_pet.is_none());
 }
 
+#[tokio::test]
+async fn added_history_uses_pet_adjusted_terminal_width() {
+    #[derive(Debug)]
+    struct WidthCell(std::sync::Arc<std::sync::atomic::AtomicU16>);
+
+    impl HistoryCell for WidthCell {
+        fn display_lines(&self, width: u16) -> Vec<Line<'static>> {
+            self.0.store(width, std::sync::atomic::Ordering::Relaxed);
+            if width == u16::MAX {
+                Vec::new()
+            } else {
+                vec!["width-sensitive history".into()]
+            }
+        }
+
+        fn raw_lines(&self) -> Vec<Line<'static>> {
+            Vec::new()
+        }
+    }
+
+    let (mut chat, mut rx, _op_rx) = make_chatwidget_manual(/*model_override*/ None).await;
+    enable_test_ambient_pet(&mut chat);
+    chat.last_rendered_width.set(Some(80));
+    set_active_cell(
+        &mut chat,
+        Box::new(PlainHistoryCell::new(vec!["active response".into()])),
+    );
+    let width = std::sync::Arc::new(std::sync::atomic::AtomicU16::new(0));
+
+    chat.add_to_history(WidthCell(std::sync::Arc::clone(&width)));
+
+    assert_eq!(width.load(std::sync::atomic::Ordering::Relaxed), 69);
+    assert!(chat.transcript.needs_final_message_separator);
+    let backend = VT100Backend::new(/*width*/ 80, /*height*/ 4);
+    let mut terminal = crate::custom_terminal::Terminal::with_options(backend).expect("terminal");
+    terminal.set_viewport_area(Rect::new(
+        /*x*/ 0, /*y*/ 3, /*width*/ 80, /*height*/ 1,
+    ));
+    for lines in drain_insert_history(&mut rx) {
+        crate::insert_history::insert_history_lines(&mut terminal, lines)
+            .expect("insert history lines");
+    }
+    insta::assert_snapshot!(terminal.backend().vt100().screen().contents().trim(), @r"
+active response
+
+width-sensitive history
+");
+
+    width.store(0, std::sync::atomic::Ordering::Relaxed);
+    chat.set_raw_output_mode(/*enabled*/ true);
+    chat.last_rendered_width.set(Some(12));
+    chat.add_to_history(WidthCell(std::sync::Arc::clone(&width)));
+    assert_eq!(width.load(std::sync::atomic::Ordering::Relaxed), 0);
+}
+
 #[tokio::test]
 #[serial]
 async fn ambient_pet_reserves_history_wrap_width() {

codex-rs/tui/src/diff_render.rs

@@ -464,8 +464,10 @@ fn render_changes_block(rows: Vec<Row<'_>>, wrap_cols: usize, cwd: &Path) -> Vec
         let lang_path = r.move_path.unwrap_or(r.path);
         let lang = detect_lang_for_path(lang_path);
         let mut lines = vec![];
-        render_change(r.change, &mut lines, wrap_cols - 4, lang.as_deref());
-        out.extend(prefix_lines(lines, "    ".into(), "    ".into()));
+        let prefix = "    ";
+        let content_width = wrap_cols.saturating_sub(prefix.len());
+        render_change(r.change, &mut lines, content_width, lang.as_deref());
+        out.extend(prefix_lines(lines, prefix.into(), prefix.into()));
     }
 
     out
@@ -1631,6 +1633,12 @@ mod tests {
             /*width*/ 80,
             /*height*/ 10,
         );
+
+        let narrow = create_diff_summary(&changes, &PathBuf::from("/"), /*wrap_cols*/ 3);
+        assert_snapshot!(format!("{}\n{}", narrow[1], narrow[2]), @r"
+            1 +a
+               l
+        ");
     }
 
     #[test]