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>

packages/builtin-tools/src/tools/ToolSearchTool/prompt.ts

@@ -1,24 +1,6 @@
-import { feature } from 'bun:bundle'
-import { isReplBridgeActive } from 'src/bootstrap/state.js'
 import { getFeatureValue_CACHED_MAY_BE_STALE } from 'src/services/analytics/growthbook.js'
 import type { Tool } from 'src/Tool.js'
-import { AGENT_TOOL_NAME } from '../AgentTool/constants.js'
-
-// Dead code elimination: Brief tool name only needed when KAIROS or KAIROS_BRIEF is on
-/* eslint-disable @typescript-eslint/no-require-imports */
-const BRIEF_TOOL_NAME: string | null =
-  feature('KAIROS') || feature('KAIROS_BRIEF')
-    ? (
-        require('../BriefTool/prompt.js') as typeof import('../BriefTool/prompt.js')
-      ).BRIEF_TOOL_NAME
-    : null
-const SEND_USER_FILE_TOOL_NAME: string | null = feature('KAIROS')
-  ? (
-      require('../SendUserFileTool/prompt.js') as typeof import('../SendUserFileTool/prompt.js')
-    ).SEND_USER_FILE_TOOL_NAME
-  : null
-
-/* eslint-enable @typescript-eslint/no-require-imports */
+import { CORE_TOOLS } from 'src/constants/tools.js'
 
 export { TOOL_SEARCH_TOOL_NAME } from './constants.js'
 
@@ -47,64 +29,26 @@ Result format: each matched tool appears as one <function>{"description": "...",
 
 Query forms:
 - "select:Read,Edit,Grep" — fetch these exact tools by name
+- "discover:schedule cron job" — pure discovery, returns tool info (name, description, schema) without loading. Use when you want to understand available tools before deciding which to invoke.
 - "notebook jupyter" — keyword search, up to max_results best matches
 - "+slack send" — require "slack" in the name, rank by remaining terms`
 
 /**
  * Check if a tool should be deferred (requires ToolSearch to load).
- * A tool is deferred if:
- * - It's an MCP tool (always deferred - workflow-specific)
- * - It has shouldDefer: true
- *
- * A tool is NEVER deferred if it has alwaysLoad: true (MCP tools set this via
- * _meta['anthropic/alwaysLoad']). This check runs first, before any other rule.
+ * A tool is deferred if it is NOT in CORE_TOOLS and does NOT have alwaysLoad: true.
+ * Core tools are always loaded — never deferred.
+ * All other tools (non-core built-in + all MCP tools) are deferred
+ * and must be discovered via ToolSearchTool / ExecuteTool.
  */
 export function isDeferredTool(tool: Tool): boolean {
-  // Explicit opt-out via _meta['anthropic/alwaysLoad'] — tool appears in the
-  // initial prompt with full schema. Checked first so MCP tools can opt out.
+  // Explicit opt-out via _meta['anthropic/alwaysLoad']
   if (tool.alwaysLoad === true) return false
 
-  // MCP tools are always deferred (workflow-specific)
-  if (tool.isMcp === true) return true
+  // Core tools are always loaded — never deferred
+  if (CORE_TOOLS.has(tool.name)) return false
 
-  // Never defer ToolSearch itself — the model needs it to load everything else
-  if (tool.name === TOOL_SEARCH_TOOL_NAME) return false
-
-  // Fork-first experiment: Agent must be available turn 1, not behind ToolSearch.
-  // Lazy require: static import of forkSubagent → coordinatorMode creates a cycle
-  // through constants/tools.ts at module init.
-  if (feature('FORK_SUBAGENT') && tool.name === AGENT_TOOL_NAME) {
-    type ForkMod = typeof import('../AgentTool/forkSubagent.js')
-    // eslint-disable-next-line @typescript-eslint/no-require-imports
-    const m = require('../AgentTool/forkSubagent.js') as ForkMod
-    if (m.isForkSubagentEnabled()) return false
-  }
-
-  // Brief is the primary communication channel whenever the tool is present.
-  // Its prompt contains the text-visibility contract, which the model must
-  // see without a ToolSearch round-trip. No runtime gate needed here: this
-  // tool's isEnabled() IS isBriefEnabled(), so being asked about its deferral
-  // status implies the gate already passed.
-  if (
-    (feature('KAIROS') || feature('KAIROS_BRIEF')) &&
-    BRIEF_TOOL_NAME &&
-    tool.name === BRIEF_TOOL_NAME
-  ) {
-    return false
-  }
-
-  // SendUserFile is a file-delivery communication channel (sibling of Brief).
-  // Must be immediately available without a ToolSearch round-trip.
-  if (
-    feature('KAIROS') &&
-    SEND_USER_FILE_TOOL_NAME &&
-    tool.name === SEND_USER_FILE_TOOL_NAME &&
-    isReplBridgeActive()
-  ) {
-    return false
-  }
-
-  return tool.shouldDefer === true
+  // Everything else (non-core built-in + all MCP tools) is deferred
+  return true
 }
 
 /**