feat(usage): 改进请求追踪与缓存预热

- 区分请求重试与故障转移：新增 has_retry 标识亲和缓存重试
- 修正候选 TTFB 计算：记录候选自身的首字节时间而非全局时间
- Streaming 状态同步 rate_multiplier，支持按 API 格式配置
- 新增缓存预热服务：启动时预热仪表盘统计、热力图、每日统计
- 优化缓存 TTL 配置：仪表盘统计 2 分钟、热力图和每日统计 10 分钟
- 自动刷新间隔从 10 秒调整为 5 秒

src/services/system/cache_warmup.py

@@ -0,0 +1,159 @@
+"""
+缓存预热服务
+
+在应用启动时预热关键缓存，避免用户首次访问时的长时间等待。
+
+预热的缓存包括：
+- 管理员仪表盘统计数据
+- 管理员热力图数据
+- 每日统计数据
+"""
+
+import asyncio
+import time
+from dataclasses import dataclass, field
+from typing import Any, Dict
+
+from sqlalchemy.orm import Session
+
+from src.core.logger import logger
+from src.database import create_session
+
+
+@dataclass
+class WarmupContext:
+    """缓存预热专用的简化 Context"""
+
+    db: Session
+    user: Any  # User model
+    audit_metadata: Dict[str, Any] = field(default_factory=dict)
+
+    def add_audit_metadata(self, **kwargs: Any) -> None:
+        """兼容 ApiRequestContext 接口"""
+        self.audit_metadata.update(kwargs)
+
+
+class CacheWarmupService:
+    """缓存预热服务"""
+
+    @classmethod
+    async def warmup_all(cls, delay_seconds: float = 3.0) -> None:
+        """
+        预热所有关键缓存
+
+        Args:
+            delay_seconds: 启动后延迟执行的秒数，确保系统完全就绪
+        """
+        await asyncio.sleep(delay_seconds)
+
+        logger.info("开始预热关键缓存...")
+        start_time = time.time()
+
+        results = await asyncio.gather(
+            cls._warmup_admin_dashboard_stats(),
+            cls._warmup_admin_heatmap(),
+            cls._warmup_daily_stats(),
+            return_exceptions=True,
+        )
+
+        success_count = sum(1 for r in results if r is True)
+        error_count = sum(1 for r in results if isinstance(r, Exception))
+        elapsed = time.time() - start_time
+
+        if error_count > 0:
+            logger.warning(f"缓存预热完成: {success_count}/3 成功, {error_count} 失败, 耗时 {elapsed:.2f}s")
+        else:
+            logger.info(f"缓存预热完成: {success_count}/3 成功, 耗时 {elapsed:.2f}s")
+
+    @classmethod
+    async def _warmup_admin_dashboard_stats(cls) -> bool:
+        """预热管理员仪表盘统计缓存"""
+        db = None
+        try:
+            from src.api.dashboard.routes import AdminDashboardStatsAdapter
+            from src.models.database import User as DBUser
+
+            db = create_session()
+
+            # 获取一个管理员用户用于构造 context
+            admin_user = db.query(DBUser).filter(DBUser.role == "admin").first()
+            if not admin_user:
+                logger.info("缓存预热: 无管理员用户，跳过仪表盘统计预热")
+                return True
+
+            context = WarmupContext(db=db, user=admin_user)
+            adapter = AdminDashboardStatsAdapter()
+            await adapter.handle(context)
+
+            logger.debug("缓存预热: 管理员仪表盘统计已预热")
+            return True
+
+        except Exception as e:
+            logger.warning(f"缓存预热失败 (仪表盘统计): {e}")
+            return False
+        finally:
+            if db:
+                db.close()
+
+    @classmethod
+    async def _warmup_admin_heatmap(cls) -> bool:
+        """预热管理员热力图缓存"""
+        db = None
+        try:
+            from src.services.usage.service import UsageService
+
+            db = create_session()
+
+            # 预热全局热力图（管理员视角）
+            await UsageService.get_cached_heatmap(
+                db=db,
+                user_id=None,
+                include_actual_cost=True,
+            )
+
+            logger.debug("缓存预热: 管理员热力图已预热")
+            return True
+
+        except Exception as e:
+            logger.warning(f"缓存预热失败 (热力图): {e}")
+            return False
+        finally:
+            if db:
+                db.close()
+
+    @classmethod
+    async def _warmup_daily_stats(cls) -> bool:
+        """预热每日统计缓存"""
+        db = None
+        try:
+            from src.api.dashboard.routes import DashboardDailyStatsAdapter
+            from src.models.database import User as DBUser
+
+            db = create_session()
+
+            # 获取一个管理员用户
+            admin_user = db.query(DBUser).filter(DBUser.role == "admin").first()
+            if not admin_user:
+                logger.info("缓存预热: 无管理员用户，跳过每日统计预热")
+                return True
+
+            context = WarmupContext(db=db, user=admin_user)
+
+            # 预热 7 天的每日统计
+            adapter = DashboardDailyStatsAdapter(days=7)
+            await adapter.handle(context)
+
+            logger.debug("缓存预热: 每日统计已预热")
+            return True
+
+        except Exception as e:
+            logger.warning(f"缓存预热失败 (每日统计): {e}")
+            return False
+        finally:
+            if db:
+                db.close()
+
+
+async def start_cache_warmup() -> None:
+    """启动缓存预热（作为后台任务）"""
+    asyncio.create_task(CacheWarmupService.warmup_all())