feat(core): 实现 Token 消耗统计系统

- 扩展 SessionStats schema 添加 token 统计字段
- 添加 TokenUsageInfo 类型和 ChatResult.usage 字段
- AgentMessageHandler 从 AI SDK response 提取 usage
- AgentExecutor 返回 usage 到执行结果
- 新增 TokenStatsManager 管理统计:
  - updateSessionStats: 更新会话 token 统计
  - mergeChildSessionStats: 合并子会话统计到父会话
  - getSessionStats/getProjectStats: 查询统计
- Agent.chat() 完成后自动更新统计
- Task 工具完成后合并子会话统计
- 新增 REST API: /api/stats/sessions/:id, /api/stats/projects/:id
- 添加 TokenStatsManager 单元测试 (12 tests)

packages/core/src/agent/executor.ts

@@ -6,7 +6,7 @@ import {
   type Tool as AITool,
   type LanguageModel,
 } from 'ai';
-import type { Tool, ToolResult, AgentConfig, ContentBlock } from '../types/index.js';
+import type { Tool, ToolResult, AgentConfig, ContentBlock, TokenUsageInfo } from '../types/index.js';
 import { buildZodSchema } from '../types/index.js';
 import { ToolRegistry } from '../tools/registry.js';
 import type {
@@ -95,6 +95,7 @@ export class AgentExecutor {
 
     let fullResponse = '';
     let steps = 0;
+    let usage: TokenUsageInfo | undefined;
 
     // 工具调用时间追踪（用于计算持续时间）
     const toolStartTimes = new Map<string, number>();
@@ -200,7 +201,9 @@ export class AgentExecutor {
           }
         }
 
-        await result.response;
+        const response = await result.response;
+        // 提取 usage 信息
+        usage = this.extractUsage(response);
       } else {
         // 非流式模式
         const result = await generateText({
@@ -214,6 +217,8 @@ export class AgentExecutor {
 
         fullResponse = result.text;
         steps = result.steps.length;
+        // 提取 usage 信息
+        usage = this.extractUsage(result.response);
       }
 
       return {
@@ -221,6 +226,7 @@ export class AgentExecutor {
         text: fullResponse,
         steps,
         sessionId: context.parentSessionId ?? 'standalone',
+        usage,
       };
     } catch (error) {
       const errorMessage = error instanceof Error ? error.message : String(error);
@@ -416,4 +422,27 @@ export class AgentExecutor {
 
     return blocks;
   }
+
+  /**
+   * 从 AI SDK 响应中提取 usage 信息
+   */
+  private extractUsage(response: unknown): TokenUsageInfo | undefined {
+    // AI SDK 的 response 对象包含 usage 字段
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    const resp = response as any;
+    const usage = resp?.usage;
+
+    if (!usage) {
+      return undefined;
+    }
+
+    return {
+      promptTokens: usage.promptTokens ?? 0,
+      completionTokens: usage.completionTokens ?? 0,
+      totalTokens: usage.totalTokens ?? (usage.promptTokens ?? 0) + (usage.completionTokens ?? 0),
+      // Anthropic API 特有的缓存字段
+      cacheReadInputTokens: usage.cacheReadInputTokens,
+      cacheCreationInputTokens: usage.cacheCreationInputTokens,
+    };
+  }
 }