feat(core): Disable todos for 3 family. (#85)

* feat(core): Disable todos for 3 family.

* tidy

packages/core/src/config/config.test.ts

@@ -766,6 +766,40 @@ describe('Server Config (config.ts)', () => {
     });
   });
 
+  describe('UseWriteTodos Configuration', () => {
+    it('should default useWriteTodos to true when not provided', () => {
+      const config = new Config(baseParams);
+      expect(config.getUseWriteTodos()).toBe(true);
+    });
+
+    it('should set useWriteTodos to false when provided as false', () => {
+      const params: ConfigParameters = {
+        ...baseParams,
+        useWriteTodos: false,
+      };
+      const config = new Config(params);
+      expect(config.getUseWriteTodos()).toBe(false);
+    });
+
+    it('should disable useWriteTodos for preview models', () => {
+      const params: ConfigParameters = {
+        ...baseParams,
+        model: 'gemini-3-pro-preview',
+      };
+      const config = new Config(params);
+      expect(config.getUseWriteTodos()).toBe(false);
+    });
+
+    it('should NOT disable useWriteTodos for non-preview models', () => {
+      const params: ConfigParameters = {
+        ...baseParams,
+        model: 'gemini-2.5-pro',
+      };
+      const config = new Config(params);
+      expect(config.getUseWriteTodos()).toBe(true);
+    });
+  });
+
   describe('Shell Tool Inactivity Timeout', () => {
     it('should default to 300000ms (300 seconds) when not provided', () => {
       const config = new Config(baseParams);

packages/core/src/config/config.ts

@@ -49,6 +49,7 @@ import {
   DEFAULT_GEMINI_EMBEDDING_MODEL,
   DEFAULT_GEMINI_FLASH_MODEL,
   DEFAULT_THINKING_MODE,
+  isPreviewModel,
 } from './models.js';
 import { shouldAttemptBrowserLaunch } from '../utils/browser.js';
 import type { MCPOAuthConfig } from '../mcp/oauth-provider.js';
@@ -549,7 +550,10 @@ export class Config {
       params.truncateToolOutputLines ?? DEFAULT_TRUNCATE_TOOL_OUTPUT_LINES;
     this.enableToolOutputTruncation = params.enableToolOutputTruncation ?? true;
     this.useSmartEdit = params.useSmartEdit ?? true;
-    this.useWriteTodos = params.useWriteTodos ?? true;
+    // // TODO(joshualitt): Re-evaluate the todo tool for 3 family.
+    this.useWriteTodos = isPreviewModel(this.model)
+      ? false
+      : (params.useWriteTodos ?? true);
     this.enableHooks = params.enableHooks ?? false;
     this.disabledHooks =
       (params.hooks && 'disabled' in params.hooks