Avoid redundant TUI redraws while streaming (#34049)

## What changed

- Redraw assistant and plan stream tails only when a completed line changes the visible tail.
- Cache the first reasoning header and update the status indicator only when its visible state changes, while restoring the cached header if the indicator is recreated.
- Keep regular commit ticks able to clear stale stream tails.

## Testing

- Add coverage for unchanged partial deltas, changed newline-delimited tails, reasoning-header redraws, recreated status indicators, stale plan tails, and history-line draw scheduling.

GitOrigin-RevId: 9016175f97ef2db2edc2fd5ba13a4d731dc2d98c

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

@@ -179,6 +179,7 @@ impl ChatWidget {
             newly_installed_marketplace_tab_id: None,
             interrupts: InterruptManager::new(),
             reasoning_buffer: String::new(),
+            reasoning_header: None,
             reasoning_summary_parts: Vec::new(),
             status_state: StatusState::default(),
             review: ReviewState::default(),

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

@@ -42,6 +42,7 @@ impl ChatWidget {
                     // Submitted is emitted when user submits.
                     // Reset any reasoning header only when we are actually submitting a turn.
                     self.reasoning_buffer.clear();
+                    self.reasoning_header = None;
                     self.reasoning_summary_parts.clear();
                     self.set_status_header(String::from("Working"));
                     self.submit_user_message(user_message);

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

@@ -739,6 +739,7 @@ impl ChatWidget {
                 );
                 if self.is_session_configured() {
                     self.reasoning_buffer.clear();
+                    self.reasoning_header = None;
                     self.reasoning_summary_parts.clear();
                     self.set_status_header(String::from("Working"));
                     self.submit_user_message(user_message);

codex-rs/tui/src/chatwidget/snapshots/codex_tui__chatwidget__tests__reasoning_delta_restores_recreated_status_indicator.snap

@@ -0,0 +1,11 @@
+---
+source: tui/src/chatwidget/tests/status_and_layout.rs
+expression: normalized_backend_snapshot(terminal.backend())
+---
+"                                                                                "
+"• Checking files (0s • esc to interrupt) · 1 background terminal running · /ps …"
+"                                                                                "
+"                                                                                "
+"› Ask Codex to do anything                                                      "
+"                                                                                "
+"  gpt-5.6-sol default · /tmp/project                                            "

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

@@ -9,14 +9,15 @@ use super::*;
 impl ChatWidget {
     /// Update the status indicator header and details.
     ///
-    /// Passing `None` clears any existing details.
+    /// Passing `None` clears any existing details. Returns whether the visible status indicator
+    /// requested a redraw.
     pub(super) fn set_status(
         &mut self,
         header: String,
         details: Option<String>,
         details_capitalization: StatusDetailsCapitalization,
         details_max_lines: usize,
-    ) {
+    ) -> bool {
         let details = details
             .filter(|details| !details.is_empty())
             .map(|details| {
@@ -33,7 +34,7 @@ impl ChatWidget {
             details: details.clone(),
             details_max_lines,
         });
-        self.bottom_pane.update_status(
+        let status_indicator_updated = self.bottom_pane.update_status(
             header,
             details,
             StatusDetailsCapitalization::Preserve,
@@ -51,17 +52,19 @@ impl ChatWidget {
         if title_uses_status {
             self.refresh_status_surfaces();
         }
+        status_indicator_updated
     }
 
     /// Convenience wrapper around [`Self::set_status`];
-    /// updates the status indicator header and clears any existing details.
-    pub(super) fn set_status_header(&mut self, header: String) {
+    /// updates the status indicator header and clears any existing details, returning whether the
+    /// visible status indicator requested a redraw.
+    pub(super) fn set_status_header(&mut self, header: String) -> bool {
         self.set_status(
             header,
             /*details*/ None,
             StatusDetailsCapitalization::CapitalizeFirst,
             STATUS_DETAILS_DEFAULT_MAX_LINES,
-        );
+        )
     }
 
     /// Sets the currently rendered footer status-line value.

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

@@ -7,7 +7,10 @@ use super::*;
 
 impl ChatWidget {
     pub(super) fn restore_reasoning_status_header(&mut self) {
-        if let Some(header) = extract_first_bold(&self.reasoning_buffer) {
+        if self.reasoning_header.is_none() {
+            self.reasoning_header = extract_first_bold(&self.reasoning_buffer);
+        }
+        if let Some(header) = self.reasoning_header.clone() {
             self.status_state.terminal_title_status_kind = TerminalTitleStatusKind::Thinking;
             self.set_status_header(header);
         } else if self.bottom_pane.is_task_running() {
@@ -149,8 +152,10 @@ impl ChatWidget {
             self.app_event_tx.send(AppEvent::StartCommitAnimation);
             self.run_catch_up_commit_tick();
         }
-        self.sync_active_stream_tail();
-        self.request_redraw();
+        // Unterminated source is buffered by the controller and cannot change the visible tail.
+        if delta.contains('\n') && self.sync_active_stream_tail() {
+            self.request_redraw();
+        }
     }
 
     pub(super) fn on_plan_item_completed(&mut self, text: String) {
@@ -213,24 +218,41 @@ impl ChatWidget {
         self.reasoning_buffer.push_str(&delta);
 
         if self.safety_buffering_is_waiting() {
-            self.request_redraw();
             return;
         }
 
         if self.unified_exec_wait_streak.is_some() {
             // Unified exec waiting should take precedence over reasoning-derived status headers.
-            self.request_redraw();
             return;
         }
 
-        if let Some(header) = extract_first_bold(&self.reasoning_buffer) {
-            // Update the shimmer header to the extracted reasoning chunk header.
-            self.status_state.terminal_title_status_kind = TerminalTitleStatusKind::Thinking;
-            self.set_status_header(header);
-        } else {
+        if self.reasoning_header.is_none() {
+            self.reasoning_header = extract_first_bold(&self.reasoning_buffer);
+        }
+        let Some(header) = self.reasoning_header.as_deref() else {
             // Fallback while we don't yet have a bold header: leave existing header as-is.
+            return;
+        };
+
+        let status = &self.status_state.current_status;
+        if self.status_state.terminal_title_status_kind == TerminalTitleStatusKind::Thinking
+            && status.header == header
+            && status.details.is_none()
+            && status.details_max_lines == STATUS_DETAILS_DEFAULT_MAX_LINES
+            && self
+                .bottom_pane
+                .status_widget()
+                .is_none_or(|status| status.header() == header)
+        {
+            return;
+        }
+
+        // Update the shimmer header to the extracted reasoning chunk header.
+        let header = header.to_string();
+        self.status_state.terminal_title_status_kind = TerminalTitleStatusKind::Thinking;
+        if !self.set_status_header(header) {
+            self.request_redraw();
         }
-        self.request_redraw();
     }
 
     pub(super) fn on_agent_reasoning_final(&mut self) {
@@ -245,6 +267,7 @@ impl ChatWidget {
             self.add_boxed_history(cell);
         }
         self.reasoning_buffer.clear();
+        self.reasoning_header = None;
         self.reasoning_summary_parts.clear();
         self.request_redraw();
     }
@@ -255,6 +278,7 @@ impl ChatWidget {
             self.reasoning_summary_parts
                 .push(std::mem::take(&mut self.reasoning_buffer));
         }
+        self.reasoning_header = None;
     }
 
     pub(super) fn on_stream_error(&mut self, message: String, additional_details: Option<String>) {
@@ -352,7 +376,9 @@ impl ChatWidget {
             self.bottom_pane.hide_status_indicator();
             self.add_boxed_history(cell);
         }
-        self.sync_active_stream_tail();
+        if scope == CommitTickScope::AnyMode || outcome.has_controller {
+            self.sync_active_stream_tail();
+        }
 
         if outcome.has_controller && outcome.all_idle {
             self.maybe_restore_status_indicator_after_stream_idle();
@@ -434,8 +460,10 @@ impl ChatWidget {
             self.app_event_tx.send(AppEvent::StartCommitAnimation);
             self.run_catch_up_commit_tick();
         }
-        self.sync_active_stream_tail();
-        self.request_redraw();
+        // Unterminated source is buffered by the controller and cannot change the visible tail.
+        if delta.contains('\n') && self.sync_active_stream_tail() {
+            self.request_redraw();
+        }
     }
 
     pub(super) fn active_cell_is_stream_tail(&self) -> bool {
@@ -450,47 +478,74 @@ impl ChatWidget {
             && self.active_cell_is_stream_tail()
     }
 
-    pub(super) fn sync_active_stream_tail(&mut self) {
+    pub(super) fn sync_active_stream_tail(&mut self) -> bool {
         if let Some(controller) = self.stream_controller.as_ref() {
             let tail_lines = controller.current_tail_lines();
             if tail_lines.is_empty() {
-                self.clear_active_stream_tail();
-                return;
+                return self.clear_active_stream_tail();
             }
 
             self.bottom_pane.hide_status_indicator();
-            self.transcript.active_cell =
-                Some(Box::new(history_cell::StreamingAgentTailCell::new(
-                    tail_lines,
-                    controller.tail_starts_stream(),
-                )));
+            let cell = history_cell::StreamingAgentTailCell::new(
+                tail_lines,
+                controller.tail_starts_stream(),
+            );
+            if self
+                .transcript
+                .active_cell
+                .as_ref()
+                .and_then(|active| {
+                    active
+                        .as_any()
+                        .downcast_ref::<history_cell::StreamingAgentTailCell>()
+                })
+                .is_some_and(|active| active == &cell)
+            {
+                return false;
+            }
+            self.transcript.active_cell = Some(Box::new(cell));
             self.bump_active_cell_revision();
-            return;
+            return true;
         }
 
         if let Some(controller) = self.plan_stream_controller.as_ref() {
             let tail_lines = controller.current_tail_display_lines();
             if tail_lines.is_empty() {
-                self.clear_active_stream_tail();
-                return;
+                return self.clear_active_stream_tail();
             }
 
             self.bottom_pane.hide_status_indicator();
-            self.transcript.active_cell = Some(Box::new(history_cell::StreamingPlanTailCell::new(
+            let cell = history_cell::StreamingPlanTailCell::new(
                 tail_lines,
                 !controller.tail_starts_stream(),
-            )));
+            );
+            if self
+                .transcript
+                .active_cell
+                .as_ref()
+                .and_then(|active| {
+                    active
+                        .as_any()
+                        .downcast_ref::<history_cell::StreamingPlanTailCell>()
+                })
+                .is_some_and(|active| active == &cell)
+            {
+                return false;
+            }
+            self.transcript.active_cell = Some(Box::new(cell));
             self.bump_active_cell_revision();
-            return;
+            return true;
         }
 
-        self.clear_active_stream_tail();
+        self.clear_active_stream_tail()
     }
 
-    pub(super) fn clear_active_stream_tail(&mut self) {
+    pub(super) fn clear_active_stream_tail(&mut self) -> bool {
         if self.active_cell_is_stream_tail() {
             self.transcript.active_cell = None;
             self.bump_active_cell_revision();
+            return true;
         }
+        false
     }
 }

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

@@ -154,6 +154,7 @@ pub(super) async fn make_chatwidget_manual(
         model_override,
         /*has_chatgpt_account*/ false,
         /*has_codex_backend_auth*/ false,
+        FrameRequester::test_dummy(),
     )
     .await
 }
@@ -162,6 +163,7 @@ pub(super) async fn make_chatwidget_manual_with_auth(
     model_override: Option<&str>,
     has_chatgpt_account: bool,
     has_codex_backend_auth: bool,
+    frame_requester: FrameRequester,
 ) -> (
     ChatWidget,
     tokio::sync::mpsc::UnboundedReceiver<AppEvent>,
@@ -181,7 +183,7 @@ pub(super) async fn make_chatwidget_manual_with_auth(
     let model_catalog = test_model_catalog(&cfg);
     let common = ChatWidgetInit {
         config: cfg,
-        frame_requester: FrameRequester::test_dummy(),
+        frame_requester,
         app_event_tx,
         workspace_command_runner: None,
         initial_user_message: None,

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

@@ -1174,6 +1174,28 @@ async fn plan_completion_restores_status_indicator_after_streaming_plan_output()
     assert_eq!(chat.bottom_pane.is_task_running(), true);
 }
 
+#[tokio::test]
+async fn unterminated_plan_delta_does_not_redraw_unchanged_stream_tail() {
+    let (mut chat, _rx, _op_rx) = make_chatwidget_manual(/*model_override*/ None).await;
+    chat.set_feature_enabled(Feature::CollaborationModes, /*enabled*/ true);
+    let plan_mask = collaboration_modes::mask_for_kind(chat.model_catalog.as_ref(), ModeKind::Plan)
+        .expect("expected plan collaboration mask");
+    chat.set_collaboration_mask(plan_mask);
+    chat.on_plan_delta("| Step | Owner |\n".to_string());
+    assert!(chat.active_cell_is_stream_tail());
+    let revision = chat.transcript.active_cell_revision;
+
+    let (frame_requester, mut draw_rx) = FrameRequester::test_channel();
+    chat.frame_requester = frame_requester;
+    chat.on_plan_delta("| partial".to_string());
+
+    assert_eq!(chat.transcript.active_cell_revision, revision);
+    assert!(matches!(
+        draw_rx.try_recv(),
+        Err(tokio::sync::mpsc::error::TryRecvError::Empty)
+    ));
+}
+
 #[tokio::test]
 async fn submit_user_message_queues_while_compaction_turn_is_running() {
     let (mut chat, _rx, mut op_rx) = make_chatwidget_manual(/*model_override*/ None).await;

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

@@ -1308,8 +1308,10 @@ async fn usage_command_runs_with_backend_auth_without_chatgpt_account_flag() {
 #[tokio::test]
 async fn usage_command_runs_with_backend_auth_from_widget_init() {
     let (mut chat, mut rx, _op_rx) = make_chatwidget_manual_with_auth(
-        /*model_override*/ None, /*has_chatgpt_account*/ false,
+        /*model_override*/ None,
+        /*has_chatgpt_account*/ false,
         /*has_codex_backend_auth*/ true,
+        FrameRequester::test_dummy(),
     )
     .await;
 

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

@@ -3767,6 +3767,190 @@ async fn deltas_then_same_final_message_are_rendered_snapshot() {
     );
 }
 
+#[tokio::test]
+async fn unterminated_agent_delta_does_not_redraw_unchanged_stream_tail() {
+    let (mut chat, _rx, _op_rx) = make_chatwidget_manual(/*model_override*/ None).await;
+    chat.handle_streaming_delta("| Step | Owner |\n".to_string());
+    assert!(chat.active_cell_is_stream_tail());
+    let revision = chat.transcript.active_cell_revision;
+
+    let (frame_requester, mut draw_rx) = FrameRequester::test_channel();
+    chat.frame_requester = frame_requester;
+    chat.handle_streaming_delta("| partial".to_string());
+
+    assert_eq!(chat.transcript.active_cell_revision, revision);
+    assert!(matches!(
+        draw_rx.try_recv(),
+        Err(tokio::sync::mpsc::error::TryRecvError::Empty)
+    ));
+}
+
+#[tokio::test]
+async fn newline_agent_delta_redraws_stream_tail_after_noop_catch_up() {
+    let (frame_requester, mut draw_rx) = FrameRequester::test_channel();
+    let (mut chat, _rx, _op_rx) = make_chatwidget_manual_with_auth(
+        /*model_override*/ None,
+        /*has_chatgpt_account*/ false,
+        /*has_codex_backend_auth*/ false,
+        frame_requester,
+    )
+    .await;
+    chat.on_task_started();
+    chat.handle_streaming_delta("Earlier line\n".to_string());
+    chat.on_commit_tick();
+    assert!(!chat.bottom_pane.status_indicator_visible());
+    while draw_rx.try_recv().is_ok() {}
+
+    chat.handle_streaming_delta("Intro line\n| Step | Owner |\n".to_string());
+
+    assert!(chat.active_cell_is_stream_tail());
+    assert!(
+        draw_rx.try_recv().is_ok(),
+        "expected the changed assistant stream tail to schedule a redraw",
+    );
+}
+
+#[tokio::test]
+async fn newline_plan_delta_redraws_stream_tail_after_noop_catch_up() {
+    let (frame_requester, mut draw_rx) = FrameRequester::test_channel();
+    let (mut chat, _rx, _op_rx) = make_chatwidget_manual_with_auth(
+        /*model_override*/ Some("gpt-5"),
+        /*has_chatgpt_account*/ false,
+        /*has_codex_backend_auth*/ false,
+        frame_requester,
+    )
+    .await;
+    chat.set_feature_enabled(Feature::CollaborationModes, /*enabled*/ true);
+    let plan_mask = collaboration_modes::mask_for_kind(chat.model_catalog.as_ref(), ModeKind::Plan)
+        .expect("expected plan collaboration mask");
+    chat.set_collaboration_mask(plan_mask);
+    chat.on_task_started();
+    chat.on_plan_delta("Earlier line\n".to_string());
+    chat.on_commit_tick();
+    assert!(!chat.bottom_pane.status_indicator_visible());
+    while draw_rx.try_recv().is_ok() {}
+
+    chat.on_plan_delta("Intro line\n| Step | Owner |\n".to_string());
+
+    assert!(chat.active_cell_is_stream_tail());
+    assert!(
+        draw_rx.try_recv().is_ok(),
+        "expected the changed plan stream tail to schedule a redraw",
+    );
+}
+
+#[tokio::test]
+async fn regular_commit_tick_clears_orphaned_plan_stream_tail() {
+    let (mut chat, _rx, _op_rx) = make_chatwidget_manual(Some("gpt-5")).await;
+    chat.set_feature_enabled(Feature::CollaborationModes, /*enabled*/ true);
+    let plan_mask = collaboration_modes::mask_for_kind(chat.model_catalog.as_ref(), ModeKind::Plan)
+        .expect("expected plan collaboration mask");
+    chat.set_collaboration_mask(plan_mask);
+    chat.on_task_started();
+    chat.on_plan_delta("| Step | Owner |\n".to_string());
+    assert!(chat.active_cell_is_stream_tail());
+
+    chat.on_task_started();
+    assert!(chat.active_cell_is_stream_tail());
+    chat.on_commit_tick();
+
+    assert!(!chat.active_cell_is_stream_tail());
+}
+
+#[tokio::test]
+async fn reasoning_delta_redraws_only_when_header_becomes_visible() {
+    let (mut chat, _rx, _op_rx) = make_chatwidget_manual(/*model_override*/ None).await;
+    let (frame_requester, mut draw_rx) = FrameRequester::test_channel();
+    chat.frame_requester = frame_requester;
+
+    chat.on_agent_reasoning_delta("still looking".to_string());
+    assert!(matches!(
+        draw_rx.try_recv(),
+        Err(tokio::sync::mpsc::error::TryRecvError::Empty)
+    ));
+    assert_eq!(chat.reasoning_header, None);
+
+    chat.on_agent_reasoning_delta(" **Checking".to_string());
+    assert!(matches!(
+        draw_rx.try_recv(),
+        Err(tokio::sync::mpsc::error::TryRecvError::Empty)
+    ));
+
+    chat.on_agent_reasoning_delta(" files**".to_string());
+    assert!(draw_rx.try_recv().is_ok());
+    assert_eq!(chat.reasoning_header.as_deref(), Some("Checking files"));
+
+    chat.on_agent_reasoning_delta(" and preparing a response".to_string());
+    assert!(matches!(
+        draw_rx.try_recv(),
+        Err(tokio::sync::mpsc::error::TryRecvError::Empty)
+    ));
+}
+
+#[tokio::test]
+async fn reasoning_delta_does_not_double_schedule_visible_status_redraw() {
+    let (frame_requester, mut draw_rx) = FrameRequester::test_channel();
+    let (mut chat, _rx, _op_rx) = make_chatwidget_manual_with_auth(
+        /*model_override*/ None,
+        /*has_chatgpt_account*/ false,
+        /*has_codex_backend_auth*/ false,
+        frame_requester,
+    )
+    .await;
+    chat.on_task_started();
+    assert!(chat.bottom_pane.status_indicator_visible());
+    while draw_rx.try_recv().is_ok() {}
+
+    chat.on_agent_reasoning_delta("**Checking files**".to_string());
+
+    assert_eq!(chat.reasoning_header.as_deref(), Some("Checking files"));
+    assert!(draw_rx.try_recv().is_ok());
+    assert!(matches!(
+        draw_rx.try_recv(),
+        Err(tokio::sync::mpsc::error::TryRecvError::Empty)
+    ));
+}
+
+#[tokio::test]
+async fn reasoning_delta_restores_recreated_status_indicator_header() {
+    let (mut chat, mut rx, _op_rx) = make_chatwidget_manual(/*model_override*/ None).await;
+    chat.on_task_started();
+    chat.on_agent_reasoning_delta("**Checking files**".to_string());
+
+    chat.on_agent_message_delta("Preamble line\n".to_string());
+    chat.on_commit_tick();
+    drain_insert_history(&mut rx);
+    assert!(!chat.bottom_pane.status_indicator_visible());
+
+    begin_unified_exec_startup(&mut chat, "call-1", "proc-1", "sleep 2");
+    let status = chat
+        .bottom_pane
+        .status_widget()
+        .expect("status indicator should be recreated");
+    assert_eq!(status.header(), "Working");
+
+    chat.on_agent_reasoning_delta(" and preparing a response".to_string());
+
+    let status = chat
+        .bottom_pane
+        .status_widget()
+        .expect("status indicator should remain visible");
+    assert_eq!(status.header(), "Checking files");
+
+    let width: u16 = 80;
+    let height = chat.desired_height(width);
+    let mut terminal = ratatui::Terminal::new(ratatui::backend::TestBackend::new(width, height))
+        .expect("create terminal");
+    terminal.set_viewport_area(Rect::new(/*x*/ 0, /*y*/ 0, width, height));
+    terminal
+        .draw(|frame| chat.render(frame.area(), frame.buffer_mut()))
+        .expect("draw restored reasoning status");
+    assert_chatwidget_snapshot!(
+        "reasoning_delta_restores_recreated_status_indicator",
+        normalized_backend_snapshot(terminal.backend())
+    );
+}
+
 #[tokio::test]
 async fn user_prompt_submit_app_server_hook_notifications_render_snapshot() {
     let (mut chat, mut rx, _op_rx) = make_chatwidget_manual(/*model_override*/ None).await;

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

@@ -82,6 +82,7 @@ impl ChatWidget {
         }
         self.reasoning_summary_parts.clear();
         self.reasoning_buffer.clear();
+        self.reasoning_header = None;
         self.set_ambient_pet_notification(
             crate::pets::PetNotificationKind::Running,
             /*body*/ None,