feat: 十轮网关优化 - 安全加固/可观测性/性能/可靠性

- SSE Keepalive Ping (15s心跳防止代理断连)
- Timing HTTP 头 (X-Timing-Queue/Inference/Total-Ms)
- Adapter Request-ID 传播到后端
- Session 清理日志回调
- Server 安全加固 (ReadHeaderTimeout/MaxHeaderBytes 防 slowloris)
- Usage Tracker 数据保留清理 (retentionDays + 定期清理)
- Config Reload 后 Adapter Registry 更新 (RegisterIfAbsent + RWMutex)
- Rate Limiter 空闲 Bucket 清理 (30分钟过期)
- Shutdown Drain 超时可配置 (ShutdownDrainSeconds)
- Config 模型字段校验增强 (provider/endpoint/actual_model)
- Auth 过期 Key 自动清理 (5分钟扫描)
- Admin API Rate Limiting
- Adapter Health Check 独立超时 (每个 adapter 3s)
- TCP 连接阶段超时 (DialContext 5s + KeepAlive 30s)
- 幂等键缓存、审计日志、Gzip 中间件、CORS Expose Headers
- Backpressure 响应头、熔断器 Prometheus 指标
- 连接池优化、Trace-ID 全链路传播

internal/scheduler/circuit_breaker.go

@@ -7,27 +7,27 @@ import (
 
 // CircuitBreaker implements a sliding-window circuit breaker for adapter health.
 type CircuitBreaker struct {
-	mu                sync.Mutex
+	mu                 sync.Mutex
 	errorRateThreshold float64
-	minRequests       int
-	windowSeconds     int
-	openDuration      time.Duration
-	halfOpenMax       int
+	minRequests        int
+	windowSeconds      int
+	openDuration       time.Duration
+	halfOpenMax        int
 
 	// sliding window state
-	requests  []time.Time
+	requests []time.Time
 	errors   []time.Time
 
 	// breaker state
-	state       breakerState
-	openedAt    time.Time
+	state         breakerState
+	openedAt      time.Time
 	halfOpenCount int
 }
 
 type breakerState int
 
 const (
-	breakerClosed   breakerState = iota
+	breakerClosed breakerState = iota
 	breakerOpen
 	breakerHalfOpen
 )
@@ -126,6 +126,53 @@ func (cb *CircuitBreaker) State() string {
 	return "unknown"
 }
 
+// BreakerStats 熔断器统计信息。
+type BreakerStats struct {
+	State         string  `json:"state"`
+	TotalRequests int     `json:"total_requests"`
+	TotalErrors   int     `json:"total_errors"`
+	ErrorRate     float64 `json:"error_rate"`
+	WindowSeconds int     `json:"window_seconds"`
+	OpenDuration  string  `json:"open_duration"`
+	Threshold     float64 `json:"error_rate_threshold"`
+	MinRequests   int     `json:"min_requests"`
+}
+
+// Stats 返回熔断器的详细统计信息。
+func (cb *CircuitBreaker) Stats() BreakerStats {
+	cb.mu.Lock()
+	defer cb.mu.Unlock()
+
+	now := time.Now()
+	cb.prune(now)
+
+	total := len(cb.requests)
+	errors := len(cb.errors)
+	var errorRate float64
+	if total > 0 {
+		errorRate = float64(errors) / float64(total)
+	}
+
+	stateName := "closed"
+	switch cb.state {
+	case breakerOpen:
+		stateName = "open"
+	case breakerHalfOpen:
+		stateName = "half_open"
+	}
+
+	return BreakerStats{
+		State:         stateName,
+		TotalRequests: total,
+		TotalErrors:   errors,
+		ErrorRate:     errorRate,
+		WindowSeconds: cb.windowSeconds,
+		OpenDuration:  cb.openDuration.String(),
+		Threshold:     cb.errorRateThreshold,
+		MinRequests:   cb.minRequests,
+	}
+}
+
 // prune removes entries outside the sliding window.
 func (cb *CircuitBreaker) prune(now time.Time) {
 	cutoff := now.Add(-time.Duration(cb.windowSeconds) * time.Second)