diff --git a/internal/ai/runtime/graphs/handoff_graph.go b/internal/ai/runtime/graphs/handoff_graph.go
index 0a0170b..7fd401a 100644
--- a/internal/ai/runtime/graphs/handoff_graph.go
+++ b/internal/ai/runtime/graphs/handoff_graph.go
@@ -22,6 +22,10 @@ type HandoffGraphInterruptInfo struct {
 	Message string `json:"message"`
 }
 
+type handoffGraphArgs struct {
+	Reason string `json:"reason"`
+}
+
 func init() {
 	schema.RegisterName[HandoffGraphState]("cs_agent_handoff_graph_state")
 	schema.RegisterName[HandoffGraphInterruptInfo]("cs_agent_handoff_graph_interrupt_info")
@@ -92,13 +96,13 @@ func (g *HandoffGraph) Run(ctx context.Context, argumentsInJSON string) (string,
 
 func (g *HandoffGraph) buildReason(argumentsInJSON string) (string, error) {
 	reason := "用户需要转人工支持"
-	raw := make(map[string]any)
+	var args handoffGraphArgs
 	if strings.TrimSpace(argumentsInJSON) != "" {
-		if err := json.Unmarshal([]byte(argumentsInJSON), &raw); err != nil {
+		if err := json.Unmarshal([]byte(argumentsInJSON), &args); err != nil {
 			return "", fmt.Errorf("invalid handoff arguments: %w", err)
 		}
 	}
-	if parsed := strings.TrimSpace(graphGetStringValue(raw, "reason")); parsed != "" {
+	if parsed := strings.TrimSpace(args.Reason); parsed != "" {
 		reason = parsed
 	}
 	return reason, nil
@@ -111,15 +115,3 @@ func (g *HandoffGraph) buildConfirmationPrompt(reason string) string {
 func parseHandoffDecision(value string) ConfirmationDecision {
 	return ParseConfirmationDecision(value)
 }
-
-func graphGetStringValue(data map[string]any, key string) string {
-	if len(data) == 0 {
-		return ""
-	}
-	value, ok := data[key]
-	if !ok || value == nil {
-		return ""
-	}
-	text, _ := value.(string)
-	return text
-}
diff --git a/internal/ai/runtime/graphs/handoff_graph_test.go b/internal/ai/runtime/graphs/handoff_graph_test.go
new file mode 100644
index 0000000..b6f469d
--- /dev/null
+++ b/internal/ai/runtime/graphs/handoff_graph_test.go
@@ -0,0 +1,31 @@
+package graphs
+
+import (
+	"testing"
+
+	"cs-agent/internal/models"
+)
+
+func TestHandoffGraphBuildReason(t *testing.T) {
+	graph := NewHandoffGraph(&models.Conversation{ID: 1}, &models.AIAgent{Name: "AI"})
+
+	reason, err := graph.buildReason(`{"reason":"  用户需要人工确认  "}`)
+	if err != nil {
+		t.Fatalf("buildReason returned error: %v", err)
+	}
+	if reason != "用户需要人工确认" {
+		t.Fatalf("unexpected reason: %q", reason)
+	}
+}
+
+func TestHandoffGraphBuildReasonFallback(t *testing.T) {
+	graph := NewHandoffGraph(&models.Conversation{ID: 1}, &models.AIAgent{Name: "AI"})
+
+	reason, err := graph.buildReason(`{}`)
+	if err != nil {
+		t.Fatalf("buildReason returned error: %v", err)
+	}
+	if reason != "用户需要转人工支持" {
+		t.Fatalf("unexpected fallback reason: %q", reason)
+	}
+}