fix(server): resolve latest available agent thread

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)
+	}
+}