Support changing reasoning effort (#2435)

https://github.com/user-attachments/assets/50198ee8-5915-47a3-bb71-69af65add1ef

Building up on #2431 #2428

codex-rs/tui/src/chatwidget.rs

@@ -45,6 +45,8 @@ use crate::bottom_pane::BottomPane;
 use crate::bottom_pane::BottomPaneParams;
 use crate::bottom_pane::CancellationEvent;
 use crate::bottom_pane::InputResult;
+use crate::bottom_pane::SelectionAction;
+use crate::bottom_pane::SelectionItem;
 use crate::history_cell;
 use crate::history_cell::CommandOutput;
 use crate::history_cell::ExecCell;
@@ -58,7 +60,10 @@ mod agent;
 use self::agent::spawn_agent;
 use crate::streaming::controller::AppEventHistorySink;
 use crate::streaming::controller::StreamController;
+use codex_common::model_presets::ModelPreset;
+use codex_common::model_presets::builtin_model_presets;
 use codex_core::ConversationManager;
+use codex_core::protocol_config_types::ReasoningEffort as ReasoningEffortConfig;
 use codex_file_search::FileMatch;
 use uuid::Uuid;
 
@@ -687,6 +692,57 @@ impl ChatWidget<'_> {
         ));
     }
 
+    /// Open a popup to choose the model preset (model + reasoning effort).
+    pub(crate) fn open_model_popup(&mut self) {
+        let current_model = self.config.model.clone();
+        let current_effort = self.config.model_reasoning_effort;
+        let presets: &[ModelPreset] = builtin_model_presets();
+
+        let mut items: Vec<SelectionItem> = Vec::new();
+        for preset in presets.iter() {
+            let name = preset.label.to_string();
+            let description = Some(preset.description.to_string());
+            let is_current = preset.model == current_model && preset.effort == current_effort;
+            let model_slug = preset.model.to_string();
+            let effort = preset.effort;
+            let actions: Vec<SelectionAction> = vec![Box::new(move |tx| {
+                tx.send(AppEvent::CodexOp(Op::OverrideTurnContext {
+                    cwd: None,
+                    approval_policy: None,
+                    sandbox_policy: None,
+                    model: Some(model_slug.clone()),
+                    effort: Some(effort),
+                    summary: None,
+                }));
+                tx.send(AppEvent::UpdateModel(model_slug.clone()));
+                tx.send(AppEvent::UpdateReasoningEffort(effort));
+            })];
+            items.push(SelectionItem {
+                name,
+                description,
+                is_current,
+                actions,
+            });
+        }
+
+        self.bottom_pane.show_selection_view(
+            "Select model and reasoning level".to_string(),
+            Some("Switch between OpenAI models for this and future Codex CLI session".to_string()),
+            Some("Press Enter to confirm or Esc to go back".to_string()),
+            items,
+        );
+    }
+
+    /// Set the reasoning effort in the widget's config copy.
+    pub(crate) fn set_reasoning_effort(&mut self, effort: ReasoningEffortConfig) {
+        self.config.model_reasoning_effort = effort;
+    }
+
+    /// Set the model in the widget's config copy.
+    pub(crate) fn set_model(&mut self, model: String) {
+        self.config.model = model;
+    }
+
     pub(crate) fn add_mcp_output(&mut self) {
         if self.config.mcp_servers.is_empty() {
             self.add_to_history(&history_cell::empty_mcp_output());