Select thinking mode from the chat

docs/USER_GUIDE.md

@@ -18,7 +18,10 @@ tool work continues concurrently.
 The composer status row shows the current project and, for Git repositories,
 the current local branch. An unsaved draft can be moved with the project menu;
 saved chats keep their original project. Use the branch menu to switch local
-branches when that project's chats are idle.
+branches when that project's chats are idle. The thinking menu is preselected
+to the model's current mode: **Thinking** is the DS4 default, while **Direct**
+answers without hidden reasoning. **Think Max** is available when the context
+window is at least 393216 tokens, matching DS4's long-context requirement.
 
 The **Git** pane shows added, changed, and deleted files from the current
 worktree, including separate staged and worktree markers. Select files to stage,

src/app.rs

@@ -449,6 +449,7 @@ pub(crate) enum Message {
     CreateSession(i32),
     DraftProjectChanged(i32),
     SwitchGitBranch(String),
+    ReasoningModeChanged(ReasoningMode),
     PermissionModeChanged(PermissionMode),
     ToggleGitFile(PathBuf),
     OpenGitDiff(PathBuf),
@@ -1522,6 +1523,34 @@ impl App {
             }
             Message::DraftProjectChanged(project_id) => self.move_draft_to_project(project_id),
             Message::SwitchGitBranch(branch) => self.switch_git_branch(&branch),
+            Message::ReasoningModeChanged(mode) => {
+                if self.active_chat_count() > 0 {
+                    self.error =
+                        Some("Stop all active generations before changing thinking mode.".into());
+                } else if !self
+                    .config
+                    .generation
+                    .supported_reasoning_modes()
+                    .contains(&mode)
+                {
+                    self.error = Some(
+                        "Think Max requires a context window of at least 393216 tokens.".into(),
+                    );
+                } else {
+                    let mut config = self.config.clone();
+                    config.generation.reasoning_mode = mode;
+                    match config.save(&config_path()) {
+                        Ok(()) => {
+                            self.config = config;
+                            self.preference_draft.reasoning_mode = mode;
+                            self.error = None;
+                            #[cfg(target_os = "macos")]
+                            preferences::update_runtime_config(&self.runtime_config, &self.config);
+                        }
+                        Err(error) => self.error = Some(error),
+                    }
+                }
+            }
             Message::PermissionModeChanged(mode) => {
                 #[cfg(target_os = "macos")]
                 if self.active_tools.is_some() {

src/app/preferences.rs

@@ -345,7 +345,7 @@ fn optional_string<T: ToString>(value: Option<T>) -> String {
     value.map_or_else(String::new, |value| value.to_string())
 }
 
-fn update_runtime_config(runtime_config: &RwLock<Config>, config: &Config) {
+pub(super) fn update_runtime_config(runtime_config: &RwLock<Config>, config: &Config) {
     *runtime_config
         .write()
         .unwrap_or_else(|poisoned| poisoned.into_inner()) = config.clone();

src/app/view/chat.rs

@@ -305,6 +305,19 @@ impl App {
                 .text_size(12)
                 .padding([2, 6])
             });
+            let reasoning_mode = self.config.generation.effective_reasoning_mode();
+            let reasoning_control: Element<'_, Message> = if self.active_chat_count() > 0 {
+                text(reasoning_mode.to_string()).size(12).into()
+            } else {
+                pick_list(
+                    self.config.generation.supported_reasoning_modes(),
+                    Some(reasoning_mode),
+                    Message::ReasoningModeChanged,
+                )
+                .text_size(12)
+                .padding([2, 6])
+                .into()
+            };
             composer_content =
                 composer_content.push(
                     row![
@@ -341,6 +354,7 @@ impl App {
                         )
                         .text_size(12)
                         .padding([2, 6]),
+                        reasoning_control,
                         icon(ICON_MODEL, 16),
                         text(self.config.model.to_string()).size(12),
                         action,

src/settings.rs

@@ -8,6 +8,7 @@ pub(crate) const REASONING_MODES: [ReasoningMode; 3] = [
     ReasoningMode::Max,
     ReasoningMode::Direct,
 ];
+const STANDARD_REASONING_MODES: [ReasoningMode; 2] = [ReasoningMode::High, ReasoningMode::Direct];
 const THINK_MAX_MIN_CONTEXT: i32 = 393_216;
 const MAX_CPU_THREADS: u32 = 32;
 const MAX_MTP_DRAFT_TOKENS: i32 = 16;
@@ -555,6 +556,23 @@ impl Default for GenerationPreferences {
 }
 
 impl GenerationPreferences {
+    pub(crate) fn effective_reasoning_mode(&self) -> ReasoningMode {
+        if self.reasoning_mode == ReasoningMode::Max && self.context_tokens < THINK_MAX_MIN_CONTEXT
+        {
+            ReasoningMode::High
+        } else {
+            self.reasoning_mode
+        }
+    }
+
+    pub(crate) fn supported_reasoning_modes(&self) -> &'static [ReasoningMode] {
+        if self.context_tokens >= THINK_MAX_MIN_CONTEXT {
+            &REASONING_MODES
+        } else {
+            &STANDARD_REASONING_MODES
+        }
+    }
+
     pub(crate) fn validate(&self) -> Result<(), String> {
         if self.context_tokens <= 0 {
             return Err("Context tokens must be a positive whole number.".into());
@@ -588,13 +606,7 @@ impl GenerationPreferences {
             top_k: 0,
             stops: Vec::new(),
             seed: self.seed,
-            reasoning_mode: if self.reasoning_mode == ReasoningMode::Max
+            reasoning_mode: self.effective_reasoning_mode(),
-                && self.context_tokens < THINK_MAX_MIN_CONTEXT
-            {
-                ReasoningMode::High
-            } else {
-                self.reasoning_mode
-            },
         }
     }
 }
@@ -680,6 +692,11 @@ mod tests {
 
         let glm = defaults.turn_settings(ModelChoice::Glm52, cache);
         assert_eq!((glm.temperature, glm.top_p, glm.min_p), (1.0, 0.95, 0.0));
+        assert_eq!(
+            defaults.supported_reasoning_modes(),
+            &[ReasoningMode::High, ReasoningMode::Direct]
+        );
+        assert_eq!(defaults.effective_reasoning_mode(), ReasoningMode::High);
 
         let explicit = GenerationPreferences {
             top_p: Some(0.4),
@@ -690,6 +707,38 @@ mod tests {
         let effective = explicit.turn_settings(ModelChoice::Glm52, cache);
         assert_eq!((effective.top_p, effective.min_p), (0.4, 0.2));
         assert_eq!(effective.reasoning_mode, ReasoningMode::High);
+
+        let long_context = GenerationPreferences {
+            context_tokens: THINK_MAX_MIN_CONTEXT,
+            reasoning_mode: ReasoningMode::Max,
+            ..GenerationPreferences::default()
+        };
+        assert_eq!(long_context.supported_reasoning_modes(), &REASONING_MODES);
+        assert_eq!(long_context.effective_reasoning_mode(), ReasoningMode::Max);
+    }
+
+    #[test]
+    fn reasoning_selection_reaches_every_model_turn() {
+        let cache = KvCachePreferences::default().settings();
+        for model in crate::model::MODEL_CHOICES {
+            for mode in [ReasoningMode::Direct, ReasoningMode::High] {
+                let generation = GenerationPreferences {
+                    reasoning_mode: mode,
+                    ..GenerationPreferences::default()
+                };
+                assert_eq!(generation.turn_settings(model, cache).reasoning_mode, mode);
+            }
+
+            let generation = GenerationPreferences {
+                context_tokens: THINK_MAX_MIN_CONTEXT,
+                reasoning_mode: ReasoningMode::Max,
+                ..GenerationPreferences::default()
+            };
+            assert_eq!(
+                generation.turn_settings(model, cache).reasoning_mode,
+                ReasoningMode::Max
+            );
+        }
     }
 
     #[test]