Fix TUI context window display before first TokenCount (#13896)

The TUI was showing the raw configured `model_context_window` until the
first
`TokenCount` event arrived, even though core had already emitted the
effective
runtime window on `TurnStarted`. This made the footer, status-line
context
window, and `/status` output briefly inconsistent for models/configs
where the
effective window differs from the configured value, such as the
`gpt-5.4`
1,000,000-token override reported in #13623.

Update the TUI to cache `TurnStarted.model_context_window` immediately
so
pre-token-count displays use the runtime effective window, and add
regression
coverage for the startup path.

---------

Co-authored-by: Charles Cunningham <ccunningham@openai.com>
Co-authored-by: Codex <noreply@openai.com>

codex-rs/tui/src/app.rs

@@ -3316,7 +3316,7 @@ impl App {
     fn handle_codex_event_now(&mut self, event: Event) {
         let needs_refresh = matches!(
             event.msg,
-            EventMsg::SessionConfigured(_) | EventMsg::TokenCount(_)
+            EventMsg::SessionConfigured(_) | EventMsg::TurnStarted(_) | EventMsg::TokenCount(_)
         );
         // This guard is only for intentional thread-switch shutdowns.
         // App-exit shutdowns are tracked by `pending_shutdown_exit_thread_id`
@@ -4805,6 +4805,29 @@ mod tests {
         );
     }
 
+    #[tokio::test]
+    async fn live_turn_started_refreshes_status_line_with_runtime_context_window() {
+        let mut app = make_test_app().await;
+        app.chat_widget
+            .setup_status_line(vec![crate::bottom_pane::StatusLineItem::ContextWindowSize]);
+
+        assert_eq!(app.chat_widget.status_line_text(), None);
+
+        app.handle_codex_event_now(Event {
+            id: "turn-started".to_string(),
+            msg: EventMsg::TurnStarted(TurnStartedEvent {
+                turn_id: "turn-1".to_string(),
+                model_context_window: Some(950_000),
+                collaboration_mode_kind: Default::default(),
+            }),
+        });
+
+        assert_eq!(
+            app.chat_widget.status_line_text(),
+            Some("950K window".into())
+        );
+    }
+
     #[tokio::test]
     async fn open_agent_picker_keeps_missing_threads_for_replay() -> Result<()> {
         let mut app = make_test_app().await;

codex-rs/tui/src/chatwidget.rs

@@ -1711,6 +1711,27 @@ impl ChatWidget {
         }
     }
 
+    fn apply_turn_started_context_window(&mut self, model_context_window: Option<i64>) {
+        let info = match self.token_info.take() {
+            Some(mut info) => {
+                info.model_context_window = model_context_window;
+                info
+            }
+            None => {
+                let Some(model_context_window) = model_context_window else {
+                    return;
+                };
+                TokenUsageInfo {
+                    total_token_usage: TokenUsage::default(),
+                    last_token_usage: TokenUsage::default(),
+                    model_context_window: Some(model_context_window),
+                }
+            }
+        };
+
+        self.apply_token_info(info);
+    }
+
     fn apply_token_info(&mut self, info: TokenUsageInfo) {
         let percent = self.context_remaining_percent(&info);
         let used_tokens = self.context_used_tokens(&info, percent.is_some());
@@ -4736,8 +4757,9 @@ impl ChatWidget {
                 self.on_agent_reasoning_final();
             }
             EventMsg::AgentReasoningSectionBreak(_) => self.on_reasoning_section_break(),
-            EventMsg::TurnStarted(_) => {
+            EventMsg::TurnStarted(event) => {
                 if !is_resume_initial_replay {
+                    self.apply_turn_started_context_window(event.model_context_window);
                     self.on_task_started();
                 }
             }
@@ -8440,6 +8462,11 @@ impl ChatWidget {
         &self.config
     }
 
+    #[cfg(test)]
+    pub(crate) fn status_line_text(&self) -> Option<String> {
+        self.bottom_pane.status_line_text()
+    }
+
     pub(crate) fn clear_token_usage(&mut self) {
         self.token_info = None;
     }

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

@@ -1659,6 +1659,53 @@ async fn context_indicator_shows_used_tokens_when_window_unknown() {
     );
 }
 
+#[tokio::test]
+async fn turn_started_uses_runtime_context_window_before_first_token_count() {
+    let (mut chat, mut rx, _ops) = make_chatwidget_manual(None).await;
+
+    chat.config.model_context_window = Some(1_000_000);
+
+    chat.handle_codex_event(Event {
+        id: "turn-start".into(),
+        msg: EventMsg::TurnStarted(TurnStartedEvent {
+            turn_id: "turn-1".to_string(),
+            model_context_window: Some(950_000),
+            collaboration_mode_kind: ModeKind::Default,
+        }),
+    });
+
+    assert_eq!(
+        chat.status_line_value_for_item(&crate::bottom_pane::StatusLineItem::ContextWindowSize),
+        Some("950K window".to_string())
+    );
+    assert_eq!(chat.bottom_pane.context_window_percent(), Some(100));
+
+    chat.add_status_output();
+
+    let cells = drain_insert_history(&mut rx);
+    let context_line = cells
+        .last()
+        .expect("status output inserted")
+        .iter()
+        .map(|line| {
+            line.spans
+                .iter()
+                .map(|span| span.content.as_ref())
+                .collect::<String>()
+        })
+        .find(|line| line.contains("Context window"))
+        .expect("context window line");
+
+    assert!(
+        context_line.contains("950K"),
+        "expected /status to use TurnStarted context window, got: {context_line}"
+    );
+    assert!(
+        !context_line.contains("1M"),
+        "expected /status to avoid raw config context window, got: {context_line}"
+    );
+}
+
 #[cfg_attr(
     target_os = "macos",
     ignore = "system configuration APIs are blocked under macOS seatbelt"
@@ -1952,7 +1999,7 @@ fn lines_to_single_string(lines: &[ratatui::text::Line<'static>]) -> String {
 }
 
 fn status_line_text(chat: &ChatWidget) -> Option<String> {
-    chat.bottom_pane.status_line_text()
+    chat.status_line_text()
 }
 
 fn make_token_info(total_tokens: i64, context_window: i64) -> TokenUsageInfo {