feat: 实现 Tool Search 基础设施层（CORE_TOOLS 白名单 + TF-IDF 索引 + ExecuteTool + 搜索增强）

- 新增 CORE_TOOLS 白名单常量（31 个核心工具），重构 isDeferredTool 为白名单制判定
- 新建 TF-IDF 工具索引模块（toolIndex.ts），复用 localSearch.ts 算法函数
- 新建 ExecuteTool 跨 API provider 统一工具执行入口
- 增强 ToolSearchTool：TF-IDF 搜索路径、discover: 模式、并行搜索合并、文本模式回退
- 新增 27 个单元测试，precheck 零错误通过（4108 tests pass）

Co-Authored-By: glm-5.1[1m] <zai-org@claude-code-best.win>

src/utils/attachments.ts

@@ -1,4 +1,5 @@
 // biome-ignore-all assist/source/organizeImports: ANT-ONLY import markers must not be reordered
+import type { ToolDiscoveryResult } from '../services/toolSearch/prefetch.js'
 import {
   logEvent,
   type AnalyticsMetadata_I_VERIFIED_THIS_IS_NOT_CODE_OR_FILEPATHS,
@@ -97,6 +98,12 @@ const skillSearchModules = feature('EXPERIMENTAL_SKILL_SEARCH')
         require('../services/skillSearch/prefetch.js') as typeof import('../services/skillSearch/prefetch.js'),
     }
   : null
+const toolSearchModules = feature('EXPERIMENTAL_TOOL_SEARCH')
+  ? {
+      prefetch:
+        require('../services/toolSearch/prefetch.js') as typeof import('../services/toolSearch/prefetch.js'),
+    }
+  : null
 const autoModeStateModule = feature('TRANSCRIPT_CLASSIFIER')
   ? (require('./permissions/autoModeState.js') as typeof import('./permissions/autoModeState.js'))
   : null
@@ -553,6 +560,14 @@ export type Attachment =
         activePath?: string
       }
     }
+  | {
+      type: 'tool_discovery'
+      tools: ToolDiscoveryResult[]
+      trigger: 'assistant_turn' | 'user_input'
+      queryText: string
+      durationMs: number
+      indexSize: number
+    }
   | {
       type: 'queued_command'
       prompt: string | Array<ContentBlockParam>
@@ -830,6 +845,25 @@ export async function getAttachments(
               }),
             ]
           : []),
+        // Tool discovery on turn 0. Inter-turn discovery runs via
+        // startToolSearchPrefetch in query.ts.
+        ...(feature('EXPERIMENTAL_TOOL_SEARCH') &&
+        toolSearchModules &&
+        !options?.skipSkillDiscovery
+          ? [
+              maybe('tool_discovery', async () => {
+                if (suppressNextDiscovery) {
+                  return []
+                }
+                const result =
+                  await toolSearchModules.prefetch.getTurnZeroToolSearchPrefetch(
+                    input,
+                    context.options.tools ?? [],
+                  )
+                return result ? [result] : []
+              }),
+            ]
+          : []),
       ]
     : []
 

src/utils/messages.ts

@@ -3909,7 +3909,24 @@ Read the team config to discover your teammates' names. Check the task list peri
     }
   }
 
-  // eslint-disable-next-line @typescript-eslint/switch-exhaustiveness-check -- teammate_mailbox/team_context/skill_discovery/bagel_console handled above
+  // tool_discovery handled here (not in the switch) so the 'tool_discovery'
+  // string literal lives inside a feature()-guarded block.
+  if (feature('EXPERIMENTAL_TOOL_SEARCH')) {
+    if (attachment.type === 'tool_discovery') {
+      if (attachment.tools.length === 0) return []
+      const lines = attachment.tools.map(
+        t => `- ${t.name}: ${t.description.slice(0, 100)}`,
+      )
+      return wrapMessagesInSystemReminder([
+        createUserMessage({
+          content: `The following tools were discovered as relevant to your task. Use ExecuteTool to invoke any of them by name:\n\n${lines.join('\n')}`,
+          isMeta: true,
+        }),
+      ])
+    }
+  }
+
+  // eslint-disable-next-line @typescript-eslint/switch-exhaustiveness-check -- teammate_mailbox/team_context/skill_discovery/tool_discovery/bagel_console handled above
   switch (attachment.type) {
     case 'directory': {
       return wrapMessagesInSystemReminder([

src/utils/toolSearch.ts

@@ -1,9 +1,9 @@
 /**
  * Tool Search utilities for dynamically discovering deferred tools.
  *
- * When enabled, deferred tools (MCP and shouldDefer tools) are sent with
+ * When enabled, deferred tools (all non-core tools) are sent with
  * defer_loading: true and discovered via ToolSearchTool rather than being
- * loaded upfront.
+ * loaded upfront. Core tools are defined in CORE_TOOLS (src/constants/tools.ts).
  */
 
 import memoize from 'lodash-es/memoize.js'
@@ -152,8 +152,8 @@ const getDeferredToolTokenCount = memoize(
 )
 
 /**
- * Tool search mode. Determines how deferrable tools (MCP + shouldDefer) are
- * surfaced:
+ * Tool search mode. Determines how deferred tools (all non-core tools)
+ * are surfaced:
  *   - 'tst': Tool Search Tool — deferred tools discovered via ToolSearchTool (always enabled)
  *   - 'tst-auto': auto — tools deferred only when they exceed threshold
  *   - 'standard': tool search disabled — all tools exposed inline
@@ -167,7 +167,7 @@ export type ToolSearchMode = 'tst' | 'tst-auto' | 'standard'
  *   auto / auto:1-99      tst-auto
  *   true / auto:0         tst
  *   false / auto:100      standard
- *   (unset)               tst (default: always defer MCP and shouldDefer tools)
+ *   (unset)               tst (default: always defer non-core tools)
  */
 export function getToolSearchMode(): ToolSearchMode {
   // CLAUDE_CODE_DISABLE_EXPERIMENTAL_BETAS is a kill switch for beta API
@@ -194,7 +194,7 @@ export function getToolSearchMode(): ToolSearchMode {
 
   if (isEnvTruthy(value)) return 'tst'
   if (isEnvDefinedFalsy(process.env.ENABLE_TOOL_SEARCH)) return 'standard'
-  return 'tst' // default: always defer MCP and shouldDefer tools
+  return 'tst' // default: always defer non-core tools
 }
 
 /**