fix(engine): resolve parallel execution races and improve max steps semantics

- Fix data race in runParallelBranches where first error could be masked
- Improve MaxSteps to allow exactly N steps
- Consolidate Resume validation logic and fix silent overwrite in Graph AddNode/AddEdge
- Add sync.RWMutex to Engine for thread-safe configuration
- Fix P2 issues: Add immediate check for router output, add mutex to hooks example, add context timeout to translation example, and update docs for Checkpointer.Delete

examples/hooks/main.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"fmt"
 	"log"
+	"sync"
 	"time"
 
 	GopherGraph "github.com/unclesam-ly/GopherGraph"
@@ -82,7 +83,10 @@ func main() {
 	// ============================================================
 	// 使用 Engine 包装器，挂载所有增强能力
 	// ============================================================
-	var nodeTimings = make(map[string]time.Time)
+	var (
+		nodeTimings   = make(map[string]time.Time)
+		nodeTimingsMu sync.Mutex
+	)
 
 	engine := GopherGraph.NewEngine(cg).
 		// 1. 注册深拷贝函数，消除并发分支对 Messages 切片的数据竞争
@@ -91,13 +95,17 @@ func main() {
 		WithMaxSteps(50).
 		// 3. Pre Hook：记录节点开始时间 + 向控制台推送"流式进度"
 		WithPreNodeHook(func(ctx context.Context, name string, s AgentState) {
+			nodeTimingsMu.Lock()
 			nodeTimings[name] = time.Now()
+			nodeTimingsMu.Unlock()
 			fmt.Printf("  ⏳ [PRE ] %-15s | 消息数: %d\n", name, len(s.Messages))
 		}).
 		// 4. Post Hook：计算并打印节点耗时
 		WithPostNodeHook(func(ctx context.Context, name string, s AgentState) {
+			nodeTimingsMu.Lock()
 			elapsed := time.Since(nodeTimings[name])
-			fmt.Printf("  ✅ [POST] %-15s | 耗时: %v | 消息数: %d\n", name, elapsed.Round(time.Millisecond), len(s.Messages))
+			nodeTimingsMu.Unlock()
+			fmt.Printf("   [POST] %-15s | 耗时: %v | 消息数: %d\n", name, elapsed.Round(time.Millisecond), len(s.Messages))
 		})
 
 	fmt.Println("🚀 启动工作流...")

examples/translation/main.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"os"
 	"strings"
+	"time"
 
 	GopherGraph "github.com/unclesam-ly/GopherGraph"
 )
@@ -122,7 +123,8 @@ func main() {
 	// 包含敏感词“秘密”，会触发人工审核中断：
 	inputText := "这是一个秘密你好"
 	fmt.Printf("🚀 启动工作流，输入原文: %q\n", inputText)
-	ctx := context.Background()
+	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Minute)
+	defer cancel()
 	thread, err := cg.Start(ctx, "translator", TranslationState{InputText: inputText})
 	if err != nil {
 		fmt.Printf("运行失败: %v\n", err)