Select thinking mode from the chat

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() {