fix: 拦截 ExecuteExtraTool 直接调用未搜索的延迟工具

模型在未通过 SearchExtraTools 发现工具的情况下直接调用 ExecuteExtraTool，
因不知道工具 schema 导致参数错误（如 libraryName: undefined）。

双重修复：
1. ExecuteTool.call() 添加服务端拦截：检查目标 deferred 工具是否已被发现
2. 更新 <available-deferred-tools> 系统提示：要求先搜索再执行

Co-Authored-By: glm-5-turbo <zai-org@claude-code-best.win>

packages/builtin-tools/src/tools/ExecuteTool/__tests__/ExecuteTool.runner.ts

@@ -33,10 +33,10 @@ mock.module('src/utils/searchExtraTools.js', () => ({
   isSearchExtraToolsEnabledOptimistic: () => true,
   getAutoSearchExtraToolsCharThreshold: () => 100,
   getSearchExtraToolsMode: () => 'tst' as const,
-  isSearchExtraToolsToolAvailable: async () => true,
+  isSearchExtraToolsToolAvailable: () => true,
   isSearchExtraToolsEnabled: async () => true,
   isToolReferenceBlock: () => false,
-  extractDiscoveredToolNames: () => new Set(),
+  extractDiscoveredToolNames: () => new Set(['TestTool', 'SecretTool']),
   isDeferredToolsDeltaEnabled: () => false,
   getDeferredToolsDelta: () => null,
 }))
@@ -154,6 +154,26 @@ describe('ExecuteTool', () => {
     expect(result.newMessages).toBeDefined()
   })
 
+  test('returns error when deferred tool has not been discovered via SearchExtraTools', async () => {
+    const mockTarget = makeMockTool('UndiscoveredTool', 'result')
+    const ctx = makeContext([mockTarget])
+
+    const result = await ExecuteTool.call(
+      { tool_name: 'UndiscoveredTool', params: {} },
+      ctx,
+      async () => ({ behavior: 'allow' }),
+      { type: 'assistant', content: [], uuid: 'msg1' } as never,
+      undefined,
+    )
+
+    expect(result.data).toEqual({
+      result: null,
+      tool_name: 'UndiscoveredTool',
+    })
+    expect(result.newMessages).toBeDefined()
+    expect(result.newMessages![0].content).toContain('has not been discovered')
+  })
+
   test('has correct name', () => {
     expect(ExecuteTool.name).toBe(EXECUTE_TOOL_NAME)
   })