Add reasoning-only status surface item (#25504)

Closes #24886.

## Why
Users can configure the TUI status line and terminal title with
`model-with-reasoning`, but issue #24886 asks for a compact
reasoning-only item. That lets a setup show just `default`, `low`,
`medium`, `high`, or `xhigh` without repeating the model name.

## What changed
- Added a `reasoning` item for `/statusline` and `/title` setup flows.
- Rendered the item from the effective reasoning effort, including
collaboration-mode overrides.
- Registered `reasoning` with `codex doctor` so Codex-generated
terminal-title config is not reported as invalid.
- Updated TUI setup snapshots so the picker previews include the new
item.

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

@@ -14,7 +14,7 @@ expression: status_line_popup_snapshot(&mut chat)
   [x] thread-title          Current thread title, or thread identifier when unnamed
   [ ] model                 Current model name
   [ ] model-with-reasoning  Current model name with reasoning level
-  [ ] current-dir           Current working directory
+  [ ] reasoning             Current reasoning level
 
   my-project · feat/awesome-feature · thread title
   Press space to toggle; ←/→ to move; enter to confirm and close; esc to close

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

@@ -14,7 +14,7 @@ expression: status_line_popup_snapshot(&mut chat)
   [x] thread-title          Current thread title, or thread identifier when unnamed
   [ ] model                 Current model name
   [ ] model-with-reasoning  Current model name with reasoning level
-  [ ] current-dir           Current working directory
+  [ ] reasoning             Current reasoning level
 
   preview-live-root · feature/live-preview-branch · Live preview thread
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codex-rs/tui/src/chatwidget/snapshots/codex_tui__chatwidget__tests__status_line_setup_popup_mixed.snap

@@ -14,7 +14,7 @@ expression: status_line_popup_snapshot(&mut chat)
   [x] thread-title          Current thread title, or thread identifier when unnamed
   [ ] model                 Current model name
   [ ] model-with-reasoning  Current model name with reasoning level
-  [ ] current-dir           Current working directory
+  [ ] reasoning             Current reasoning level
 
   my-project · feature/mixed-preview · Mixed preview thread
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codex-rs/tui/src/chatwidget/snapshots/codex_tui__chatwidget__tests__status_line_setup_popup_rate_limits.snap

@@ -13,8 +13,8 @@ expression: status_line_popup_snapshot(&mut chat)
   [x] weekly-limit          Remaining usage on the weekly usage limit (omitted when unavailable)
   [ ] model                 Current model name
   [ ] model-with-reasoning  Current model name with reasoning level
+  [ ] reasoning             Current reasoning level
   [ ] current-dir           Current working directory
-  [ ] project-name          Project name (omitted when unavailable)
 
   monthly 65% left · weekly 50% left
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codex-rs/tui/src/chatwidget/status_surfaces.rs

@@ -562,6 +562,7 @@ impl ChatWidget {
         match item {
             StatusLineItem::ModelName => Some(self.model_display_name().to_string()),
             StatusLineItem::ModelWithReasoning => Some(self.model_with_reasoning_display_name()),
+            StatusLineItem::Reasoning => Some(self.reasoning_display_name().to_string()),
             StatusLineItem::CurrentDir => {
                 Some(format_directory_display(
                     self.status_line_cwd(),
@@ -694,6 +695,7 @@ impl ChatWidget {
             StatusSurfacePreviewItem::RawOutput => StatusLineItem::RawOutput,
             StatusSurfacePreviewItem::Model => StatusLineItem::ModelName,
             StatusSurfacePreviewItem::ModelWithReasoning => StatusLineItem::ModelWithReasoning,
+            StatusSurfacePreviewItem::Reasoning => StatusLineItem::Reasoning,
         };
         self.status_line_value_for_item(status_line_item)
     }
@@ -759,12 +761,20 @@ impl ChatWidget {
                 self.model_with_reasoning_display_name(),
                 /*max_chars*/ 32,
             )),
+            TerminalTitleItem::Reasoning => Some(Self::truncate_terminal_title_part(
+                self.reasoning_display_name().to_string(),
+                /*max_chars*/ 32,
+            )),
             TerminalTitleItem::TaskProgress => self.terminal_title_task_progress(),
         }
     }
 
+    fn reasoning_display_name(&self) -> &'static str {
+        Self::status_line_reasoning_effort_label(self.effective_reasoning_effort())
+    }
+
     fn model_with_reasoning_display_name(&self) -> String {
-        let label = Self::status_line_reasoning_effort_label(self.effective_reasoning_effort());
+        let label = self.reasoning_display_name();
         let service_tier_label = self
             .current_service_tier()
             .and_then(|service_tier| {

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

@@ -2208,6 +2208,37 @@ async fn terminal_title_model_updates_on_model_change_without_manual_refresh() {
     assert_eq!(chat.last_terminal_title, Some("gpt-5.3-codex".to_string()));
 }
 
+#[tokio::test]
+async fn status_line_and_terminal_title_reasoning_render_only_effort() {
+    let (mut chat, _rx, _op_rx) = make_chatwidget_manual(Some("gpt-5.4")).await;
+    chat.config.tui_status_line = Some(vec!["reasoning".to_string()]);
+    chat.config.tui_terminal_title = Some(vec!["reasoning".to_string()]);
+    chat.set_reasoning_effort(Some(ReasoningEffortConfig::XHigh));
+    chat.set_service_tier(Some(ServiceTier::Fast.request_value().to_string()));
+
+    chat.refresh_status_line();
+    chat.refresh_terminal_title();
+
+    assert_eq!(status_line_text(&chat), Some("xhigh".to_string()));
+    assert_eq!(chat.last_terminal_title, Some("xhigh".to_string()));
+}
+
+#[tokio::test]
+async fn status_line_reasoning_updates_on_mode_switch_without_manual_refresh() {
+    let (mut chat, _rx, _op_rx) = make_chatwidget_manual(Some("gpt-5.3-codex")).await;
+    chat.set_feature_enabled(Feature::CollaborationModes, /*enabled*/ true);
+    chat.config.tui_status_line = Some(vec!["reasoning".to_string()]);
+    chat.set_reasoning_effort(Some(ReasoningEffortConfig::High));
+
+    assert_eq!(status_line_text(&chat), Some("high".to_string()));
+
+    let plan_mask = collaboration_modes::plan_mask(chat.model_catalog.as_ref())
+        .expect("expected plan collaboration mode");
+    chat.set_collaboration_mask(plan_mask);
+
+    assert_eq!(status_line_text(&chat), Some("medium".to_string()));
+}
+
 #[tokio::test]
 async fn status_line_model_with_reasoning_updates_on_mode_switch_without_manual_refresh() {
     let (mut chat, _rx, _op_rx) = make_chatwidget_manual(Some("gpt-5.3-codex")).await;