fix(gateway): 修复路由引擎P0问题

P0-07: RegisterStrategy添加互斥锁保护，解决并发注册策略时的数据竞争问题
P0-08: SelectProvider添加decision nil检查，避免nil指针被传递

使用TDD方法：
1. 编写测试验证问题存在
2. 修复代码
3. 测试验证通过

gateway/internal/router/engine/routing_engine.go

@@ -3,6 +3,7 @@ package engine
 import (
 	"context"
 	"errors"
+	"sync"
 
 	"lijiaoqiao/gateway/internal/router/strategy"
 )
@@ -18,6 +19,7 @@ type RoutingMetrics interface {
 
 // RoutingEngine 路由引擎
 type RoutingEngine struct {
+	mu        sync.RWMutex
 	strategies map[string]strategy.StrategyTemplate
 	metrics    RoutingMetrics
 }
@@ -32,6 +34,8 @@ func NewRoutingEngine() *RoutingEngine {
 
 // RegisterStrategy 注册路由策略
 func (e *RoutingEngine) RegisterStrategy(name string, template strategy.StrategyTemplate) {
+	e.mu.Lock()
+	defer e.mu.Unlock()
 	e.strategies[name] = template
 }
 
@@ -54,8 +58,11 @@ func (e *RoutingEngine) SelectProvider(ctx context.Context, req *strategy.Routin
 		return nil, err
 	}
 
-	// 记录指标
-	if e.metrics != nil && decision != nil {
+	if decision == nil {
+		return nil, ErrStrategyNotFound
+	}
+
+	if e.metrics != nil {
 		e.metrics.RecordSelection(decision.Provider, decision.Strategy, decision)
 	}
 

gateway/internal/router/engine/routing_engine_test.go

@@ -152,3 +152,88 @@ func (m *MockRoutingMetrics) RecordSelection(provider string, strategyName strin
 		m.takeoverMark = decision.TakeoverMark
 	}
 }
+
+// ==================== P0问题测试 ====================
+
+// TestP0_07_RegisterStrategy_ThreadSafety 测试P0-07: 策略注册非线程安全
+func TestP0_07_RegisterStrategy_ThreadSafety(t *testing.T) {
+	engine := NewRoutingEngine()
+
+	// 并发注册多个策略，启用-race检测器可以发现数据竞争
+	done := make(chan bool)
+	const goroutines = 100
+
+	for i := 0; i < goroutines; i++ {
+		go func(idx int) {
+			name := strategyName(idx)
+			tpl := strategy.NewCostBasedTemplate(name, strategy.CostParams{
+				MaxCostPer1KTokens: 1.0,
+			})
+			tpl.RegisterProvider("ProviderA", &MockProvider{
+				name:            "ProviderA",
+				costPer1KTokens:  0.5,
+				available:       true,
+				models:          []string{"gpt-4"},
+			})
+			engine.RegisterStrategy(name, tpl)
+			done <- true
+		}(i)
+	}
+
+	// 等待所有goroutine完成
+	for i := 0; i < goroutines; i++ {
+		<-done
+	}
+
+	// 验证所有策略都已注册
+	for i := 0; i < goroutines; i++ {
+		name := strategyName(i)
+		_, ok := engine.strategies[name]
+		assert.True(t, ok, "Strategy %s should be registered", name)
+	}
+}
+
+func strategyName(idx int) string {
+	return "strategy_" + string(rune('a'+idx%26)) + string(rune('0'+idx/26%10))
+}
+
+// TestP0_08_DecisionNilPanic 测试P0-08: decision可能为空指针
+func TestP0_08_DecisionNilPanic(t *testing.T) {
+	engine := NewRoutingEngine()
+
+	// 创建一个返回nil decision但不返回错误的策略
+	nilDecisionStrategy := &NilDecisionStrategy{}
+
+	engine.RegisterStrategy("nil_decision", nilDecisionStrategy)
+
+	// 设置metrics
+	engine.metrics = &MockRoutingMetrics{}
+
+	req := &strategy.RoutingRequest{
+		Model:  "gpt-4",
+		UserID: "user123",
+	}
+
+	// 验证返回ErrStrategyNotFound而不是panic
+	decision, err := engine.SelectProvider(context.Background(), req, "nil_decision")
+
+	assert.Error(t, err, "Should return error when decision is nil")
+	assert.Equal(t, ErrStrategyNotFound, err, "Should return ErrStrategyNotFound")
+	assert.Nil(t, decision, "Decision should be nil")
+}
+
+// NilDecisionStrategy 返回nil decision的测试策略
+type NilDecisionStrategy struct{}
+
+func (s *NilDecisionStrategy) SelectProvider(ctx context.Context, req *strategy.RoutingRequest) (*strategy.RoutingDecision, error) {
+	// 返回nil decision但不返回错误 - 这模拟了潜在的边界情况
+	return nil, nil
+}
+
+func (s *NilDecisionStrategy) Name() string {
+	return "nil_decision"
+}
+
+func (s *NilDecisionStrategy) Type() string {
+	return "nil_decision"
+}