diff --git a/server/internal/logic/lovart_agent_mapper.go b/server/internal/logic/lovart_agent_mapper.go
index f4324f4..7835bd8 100644
--- a/server/internal/logic/lovart_agent_mapper.go
+++ b/server/internal/logic/lovart_agent_mapper.go
@@ -8,20 +8,24 @@ import (
 	"img_infinite_canvas/internal/types"
 )
 
-func latestLovartThreadID(project design.Project) string {
-	if threadID := strings.TrimSpace(project.LastThreadID); threadID != "" {
-		return threadID
-	}
-	for index := len(project.Messages) - 1; index >= 0; index-- {
-		message := project.Messages[index]
-		if isHiddenAgentMessage(message) {
+func latestLovartThreadID(currentThreadID string, threads []design.AgentThreadSummary) string {
+	currentThreadID = strings.TrimSpace(currentThreadID)
+	latestThreadID := ""
+	var latestTimestamp int64
+	for _, thread := range threads {
+		threadID := strings.TrimSpace(thread.AgentThreadID)
+		if threadID == "" {
 			continue
 		}
-		if threadID := strings.TrimSpace(message.ThreadID); threadID != "" {
+		if threadID == currentThreadID {
 			return threadID
 		}
+		if latestThreadID == "" || thread.UpdateTimestamp >= latestTimestamp {
+			latestThreadID = threadID
+			latestTimestamp = thread.UpdateTimestamp
+		}
 	}
-	return ""
+	return latestThreadID
 }
 
 func toCandaChatHistoryItem(message design.Message, projectID string, threadID string) types.CandaChatHistoryItem {
diff --git a/server/internal/logic/lovart_agent_mapper_test.go b/server/internal/logic/lovart_agent_mapper_test.go
new file mode 100644
index 0000000..275c637
--- /dev/null
+++ b/server/internal/logic/lovart_agent_mapper_test.go
@@ -0,0 +1,36 @@
+package logic
+
+import (
+	"testing"
+
+	"img_infinite_canvas/internal/domain/design"
+)
+
+func TestLatestLovartThreadIDKeepsCurrentNonEmptyThread(t *testing.T) {
+	threads := []design.AgentThreadSummary{
+		{AgentThreadID: "thread-current", UpdateTimestamp: 100},
+		{AgentThreadID: "thread-latest", UpdateTimestamp: 200},
+	}
+
+	if got := latestLovartThreadID("thread-current", threads); got != "thread-current" {
+		t.Fatalf("expected current non-empty thread, got %q", got)
+	}
+}
+
+func TestLatestLovartThreadIDFallsBackToLatestNonEmptyThread(t *testing.T) {
+	threads := []design.AgentThreadSummary{
+		{AgentThreadID: "thread-older", UpdateTimestamp: 100},
+		{AgentThreadID: "thread-latest", UpdateTimestamp: 300},
+		{AgentThreadID: "thread-middle", UpdateTimestamp: 200},
+	}
+
+	if got := latestLovartThreadID("thread-empty", threads); got != "thread-latest" {
+		t.Fatalf("expected latest non-empty thread, got %q", got)
+	}
+}
+
+func TestLatestLovartThreadIDStaysEmptyWithoutHistory(t *testing.T) {
+	if got := latestLovartThreadID("thread-empty", nil); got != "" {
+		t.Fatalf("expected empty thread ID, got %q", got)
+	}
+}
diff --git a/server/internal/logic/query_agent_last_thread_logic.go b/server/internal/logic/query_agent_last_thread_logic.go
index 0c32e3e..d3fe99d 100644
--- a/server/internal/logic/query_agent_last_thread_logic.go
+++ b/server/internal/logic/query_agent_last_thread_logic.go
@@ -31,10 +31,14 @@ func (l *QueryAgentLastThreadLogic) QueryAgentLastThread(req *types.QueryAgentLa
 	if err != nil {
 		return nil, err
 	}
+	threads, err := l.svcCtx.DesignService.AgentThreads(l.ctx, req.ProjectId)
+	if err != nil {
+		return nil, err
+	}
 
 	return &types.QueryAgentLastThreadResponse{
 		Code: 0,
 		Msg:  nil,
-		Data: latestLovartThreadID(project),
+		Data: latestLovartThreadID(project.LastThreadID, threads),
 	}, nil
 }