Hide Fast mode status for unsupported models (#39999)

## Why

The `fast-mode` status item showed `Fast off` even when the selected model did not support Fast mode.

## What changed

- Hide the Fast mode status value when the current model is known not to support Fast mode.
- Continue showing the value for supported and uncatalogued models.

## Testing

- Cover visibility updates when switching among supported, unsupported, and uncatalogued models.
- Update the footer snapshot to verify that an unsupported model omits the Fast mode value.

GitOrigin-RevId: c297655189efc719b2097c2aa415029b01d6873e

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

@@ -3806,7 +3806,8 @@ async fn completed_turn_clears_visible_running_hook() {
 
 #[tokio::test]
 async fn status_line_fast_mode_renders_on_and_off() {
-    let (mut chat, _rx, _op_rx) = make_chatwidget_manual(/*model_override*/ None).await;
+    let (mut chat, _rx, _op_rx) = make_chatwidget_manual(Some("gpt-5.4")).await;
+    set_fast_mode_test_catalog(&mut chat);
     chat.config.tui_status_line = Some(vec!["fast-mode".to_string()]);
 
     chat.refresh_status_line();
@@ -3817,15 +3818,40 @@ async fn status_line_fast_mode_renders_on_and_off() {
     assert_eq!(status_line_text(&chat), Some("Fast on".to_string()));
 }
 
+#[tokio::test]
+async fn status_line_fast_mode_updates_visibility_on_model_change() {
+    let (mut chat, _rx, _op_rx) = make_chatwidget_manual(Some("gpt-5.4")).await;
+    set_fast_mode_test_catalog(&mut chat);
+    chat.config.tui_status_line = Some(vec!["fast-mode".to_string()]);
+
+    chat.refresh_status_line();
+    assert_eq!(status_line_text(&chat), Some("Fast off".to_string()));
+
+    chat.set_model("gpt-5.2");
+    assert_eq!(status_line_text(&chat), None);
+
+    chat.set_model("gpt-5.4");
+    assert_eq!(status_line_text(&chat), Some("Fast off".to_string()));
+
+    chat.set_model("uncatalogued-model");
+    assert_eq!(status_line_text(&chat), Some("Fast off".to_string()));
+    chat.set_service_tier(Some(ServiceTier::Fast.request_value().to_string()));
+    assert_eq!(status_line_text(&chat), Some("Fast on".to_string()));
+}
+
 #[tokio::test]
 async fn status_line_fast_mode_footer_snapshot() {
     use ratatui::Terminal;
     use ratatui::backend::TestBackend;
 
-    let (mut chat, _rx, _op_rx) = make_chatwidget_manual(/*model_override*/ None).await;
+    let (mut chat, _rx, _op_rx) = make_chatwidget_manual(Some("gpt-5.2")).await;
+    set_fast_mode_test_catalog(&mut chat);
     chat.show_welcome_banner = false;
-    chat.config.tui_status_line = Some(vec!["fast-mode".to_string()]);
-    chat.set_service_tier(Some(ServiceTier::Fast.request_value().to_string()));
+    chat.config.tui_status_line = Some(vec![
+        "model-with-reasoning".to_string(),
+        "fast-mode".to_string(),
+    ]);
+    chat.set_reasoning_effort(Some(ReasoningEffortConfig::High));
     chat.refresh_status_line();
 
     let width = 80;