test: 补充单元测试提升代码覆盖率

新增测试文件:
- agent/executor-extended.test.ts, presets/
- context/manager-extended.test.ts
- core/agent.test.ts, providers.test.ts
- lsp/cli.test.ts, client-extended.test.ts, index.test.ts
- permission/file-prompt.test.ts, prompt.test.ts
- skills/builtin/
- tools/filesystem/write_file-extended.test.ts
- tools/git/git_commit-extended.test.ts
- tools/load_description.test.ts
- tools/todo/todo-manager.test.ts
- tools/tool-search.test.ts
- types/
- utils/config-extended.test.ts, diff-extended.test.ts

修改现有测试:
- agent/manager.test.ts
- tools/skill/skill.test.ts
- utils/config.test.ts, diff.test.ts, image.test.ts

tests/unit/tools/skill/skill.test.ts

@@ -1,5 +1,5 @@
 import { describe, it, expect, beforeEach, vi } from 'vitest';
-import { skillTool } from '../../../../src/tools/skill/skill.js';
+import { skillTool, updateSkillDescription } from '../../../../src/tools/skill/skill.js';
 import { getSkillRegistry, resetSkillRegistry } from '../../../../src/skills/registry.js';
 import type { Skill } from '../../../../src/skills/types.js';
 
@@ -144,4 +144,62 @@ describe('skillTool - Skill 工具', () => {
       expect(result.metadata?.source).toBe('builtin');
     });
   });
+
+  describe('工具描述', () => {
+    it('更新后描述包含可用 Skill 列表', () => {
+      // beforeEach 中已初始化 registry，现在更新描述
+      updateSkillDescription();
+
+      expect(skillTool.description).toContain('code-review');
+      expect(skillTool.description).toContain('代码审查');
+    });
+
+    it('更新后描述包含分类信息', () => {
+      updateSkillDescription();
+      expect(skillTool.description).toContain('[development]');
+    });
+
+    it('更新后描述包含使用示例', () => {
+      updateSkillDescription();
+      expect(skillTool.description).toContain('使用示例');
+      expect(skillTool.description).toContain('skill_name');
+    });
+
+    it('禁用的 Skill 不在描述中', () => {
+      updateSkillDescription();
+      expect(skillTool.description).not.toContain('disabled-skill');
+    });
+  });
+
+  describe('updateSkillDescription', () => {
+    it('调用后描述被更新', async () => {
+      updateSkillDescription();
+
+      // 描述应该包含当前注册的 Skill
+      expect(skillTool.description).toContain('code-review');
+      expect(typeof skillTool.description).toBe('string');
+    });
+  });
+
+  describe('边界情况', () => {
+    it('params 为 undefined 时使用空对象', async () => {
+      const result = await skillTool.execute({
+        skill_name: 'code-review',
+        // 不提供 params
+      });
+
+      expect(result.success).toBe(false);
+      expect(result.error).toContain('缺少必需参数');
+    });
+
+    it('skill_name 为空字符串时返回错误', async () => {
+      const result = await skillTool.execute({
+        skill_name: '',
+        params: {},
+      });
+
+      expect(result.success).toBe(false);
+      expect(result.error).toContain('不存在');
+    });
+  });
 });