refactor: remove Subject field from Conversation model and related logic, replace with CustomerName

internal/ai/runtime/graphs/analyze_conversation_graph.go

@@ -84,9 +84,6 @@ func buildAnalyzeConversationResult(conversation models.Conversation, messages [
 
 func buildConversationSummary(conversation models.Conversation, messages []models.Message, input AnalyzeConversationInput) string {
 	parts := make([]string, 0, 4)
-	if strings.TrimSpace(conversation.Subject) != "" {
-		parts = append(parts, "会话主题："+strings.TrimSpace(conversation.Subject))
-	}
 	if input.ObservedIssue != "" {
 		parts = append(parts, "当前问题："+input.ObservedIssue)
 	} else if strings.TrimSpace(conversation.LastMessageSummary) != "" {
@@ -103,7 +100,6 @@ func buildConversationSummary(conversation models.Conversation, messages []model
 
 func buildConversationCorpus(conversation models.Conversation, messages []models.Message, input AnalyzeConversationInput) string {
 	parts := make([]string, 0, len(messages)+4)
-	parts = append(parts, strings.TrimSpace(conversation.Subject))
 	parts = append(parts, strings.TrimSpace(conversation.LastMessageSummary))
 	parts = append(parts, input.Goal, input.ObservedIssue, input.AdditionalContext)
 	for i := range messages {
@@ -200,9 +196,6 @@ func recommendQuestions(intent string, signals []string, input AnalyzeConversati
 
 func buildConversationAnalysisFacts(conversation models.Conversation, messages []models.Message) []string {
 	facts := make([]string, 0, 4)
-	if strings.TrimSpace(conversation.Subject) != "" {
-		facts = append(facts, "会话主题："+strings.TrimSpace(conversation.Subject))
-	}
 	if strings.TrimSpace(conversation.LastMessageSummary) != "" {
 		facts = append(facts, "最近摘要："+strings.TrimSpace(conversation.LastMessageSummary))
 	}

internal/ai/runtime/graphs/analyze_conversation_graph_test.go

@@ -9,7 +9,6 @@ import (
 
 func TestBuildAnalyzeConversationResult_RecommendsHandoffForComplaint(t *testing.T) {
 	conversation := models.Conversation{
-		Subject:            "用户投诉扣费异常",
 		LastMessageSummary: "用户反馈被重复扣费，并要求人工处理",
 	}
 	messages := []models.Message{
@@ -33,7 +32,6 @@ func TestBuildAnalyzeConversationResult_RecommendsHandoffForComplaint(t *testing
 
 func TestBuildAnalyzeConversationResult_RecommendsPrepareTicket(t *testing.T) {
 	conversation := models.Conversation{
-		Subject:            "订单无法支付",
 		LastMessageSummary: "用户要求登记问题并尽快处理",
 	}
 	messages := []models.Message{

internal/ai/runtime/graphs/create_ticket_graph.go

@@ -114,7 +114,7 @@ func (g *CreateTicketGraph) buildCreateRequest(argumentsInJSON string) (request.
 	req.Priority = args.Priority
 	req.Severity = args.Severity
 	if req.Title == "" {
-		req.Title = strings.TrimSpace(g.conversation.Subject)
+		req.Title = strings.TrimSpace(g.conversation.LastMessageSummary)
 	}
 	if req.Description == "" {
 		req.Description = strings.TrimSpace(g.conversation.LastMessageSummary)

internal/ai/runtime/graphs/prepare_ticket_draft_graph.go

@@ -100,8 +100,6 @@ func buildDraftTitle(conversation models.Conversation, input PrepareTicketDraftI
 		return limitText(input.Title, 80)
 	case input.Issue != "":
 		return limitText(input.Issue, 80)
-	case strings.TrimSpace(conversation.Subject) != "":
-		return limitText(conversation.Subject, 80)
 	case strings.TrimSpace(conversation.LastMessageSummary) != "":
 		return limitText(conversation.LastMessageSummary, 80)
 	default:
@@ -144,9 +142,6 @@ func hasSufficientIssueContext(input PrepareTicketDraftInput, description string
 
 func buildConversationFacts(conversation models.Conversation, messages []models.Message) []string {
 	facts := make([]string, 0, 4)
-	if strings.TrimSpace(conversation.Subject) != "" {
-		facts = append(facts, "会话主题："+strings.TrimSpace(conversation.Subject))
-	}
 	if strings.TrimSpace(conversation.LastMessageSummary) != "" {
 		facts = append(facts, "最近摘要："+strings.TrimSpace(conversation.LastMessageSummary))
 	}

internal/ai/runtime/graphs/prepare_ticket_draft_graph_test.go

@@ -9,7 +9,6 @@ import (
 
 func TestBuildPrepareTicketDraftResult_UsesConversationFallbacks(t *testing.T) {
 	conversation := models.Conversation{
-		Subject:            "企业微信登录异常",
 		LastMessageSummary: "用户反馈企业微信扫码后页面空白，无法进入工作台",
 	}
 	messages := []models.Message{
@@ -38,7 +37,6 @@ func TestBuildPrepareTicketDraftResult_UsesConversationFallbacks(t *testing.T) {
 
 func TestBuildPrepareTicketDraftResult_ReadyWithExplicitIssue(t *testing.T) {
 	conversation := models.Conversation{
-		Subject:            "订单支付失败",
 		LastMessageSummary: "用户反馈连续支付失败",
 	}
 

internal/ai/runtime/graphs/triage_service_request_graph_test.go

@@ -9,7 +9,6 @@ import (
 
 func TestTriageServiceRequestResult_PrepareTicket(t *testing.T) {
 	conversation := models.Conversation{
-		Subject:            "支付失败需要登记工单",
 		LastMessageSummary: "用户要求建单跟进支付失败问题",
 	}
 	messages := []models.Message{
@@ -31,7 +30,6 @@ func TestTriageServiceRequestResult_PrepareTicket(t *testing.T) {
 
 func TestTriageServiceRequestResult_Handoff(t *testing.T) {
 	conversation := models.Conversation{
-		Subject:            "投诉转人工",
 		LastMessageSummary: "用户要求人工处理扣费投诉",
 	}
 	messages := []models.Message{