diff --git a/backend/internal/session/memory_test.go b/backend/internal/session/memory_test.go
index eb37b73..ba670f0 100644
--- a/backend/internal/session/memory_test.go
+++ b/backend/internal/session/memory_test.go
@@ -284,3 +284,198 @@ func TestActiveCount(t *testing.T) {
 		t.Errorf("ActiveCount = %d, want 2", m.ActiveCount())
 	}
 }
+
+func TestCreateWithUserID(t *testing.T) {
+	m := NewMemoryManager(30*time.Minute, 20)
+	defer m.Stop()
+	ctx := context.Background()
+
+	id, err := m.Create(ctx, "user-123", models.DefaultConfig())
+	if err != nil {
+		t.Fatalf("Create: %v", err)
+	}
+
+	sess, err := m.Get(ctx, id)
+	if err != nil {
+		t.Fatalf("Get: %v", err)
+	}
+	if sess.UserID != "user-123" {
+		t.Errorf("UserID = %q, want %q", sess.UserID, "user-123")
+	}
+	if sess.Title != models.DefaultSessionTitle {
+		t.Errorf("Title = %q, want %q", sess.Title, models.DefaultSessionTitle)
+	}
+	if sess.UpdatedAt.IsZero() {
+		t.Error("UpdatedAt should not be zero")
+	}
+}
+
+func TestUpdateTitle(t *testing.T) {
+	m := NewMemoryManager(30*time.Minute, 20)
+	defer m.Stop()
+	ctx := context.Background()
+
+	id, _ := m.Create(ctx, "user-1", models.DefaultConfig())
+
+	if err := m.UpdateTitle(ctx, id, "自定义标题"); err != nil {
+		t.Fatalf("UpdateTitle: %v", err)
+	}
+
+	sess, _ := m.Get(ctx, id)
+	if sess.Title != "自定义标题" {
+		t.Errorf("Title = %q, want %q", sess.Title, "自定义标题")
+	}
+}
+
+func TestUpdateTitleNotFound(t *testing.T) {
+	m := NewMemoryManager(30*time.Minute, 20)
+	defer m.Stop()
+	ctx := context.Background()
+
+	err := m.UpdateTitle(ctx, "nonexistent", "标题")
+	if err != ErrSessionNotFound {
+		t.Errorf("UpdateTitle nonexistent: err = %v, want ErrSessionNotFound", err)
+	}
+}
+
+func TestAutoTitleOnFirstMessage(t *testing.T) {
+	m := NewMemoryManager(30*time.Minute, 20)
+	defer m.Stop()
+	ctx := context.Background()
+
+	id, _ := m.Create(ctx, "user-1", models.DefaultConfig())
+
+	// 首条 user 消息应自动更新标题
+	m.AppendMessage(ctx, id, models.Message{Role: "user", Content: "你好世界"})
+
+	sess, _ := m.Get(ctx, id)
+	if sess.Title != "你好世界" {
+		t.Errorf("Title = %q, want %q", sess.Title, "你好世界")
+	}
+}
+
+func TestAutoTitleLongMessage(t *testing.T) {
+	m := NewMemoryManager(30*time.Minute, 20)
+	defer m.Stop()
+	ctx := context.Background()
+
+	id, _ := m.Create(ctx, "user-1", models.DefaultConfig())
+
+	// 超过 20 字符的消息应截断
+	longMsg := "这是一条很长很长很长很长很长很长很长很长的消息"
+	m.AppendMessage(ctx, id, models.Message{Role: "user", Content: longMsg})
+
+	sess, _ := m.Get(ctx, id)
+	expected := string([]rune(longMsg)[:20]) + "…"
+	if sess.Title != expected {
+		t.Errorf("Title = %q, want %q", sess.Title, expected)
+	}
+}
+
+func TestAutoTitleNotOverwritten(t *testing.T) {
+	m := NewMemoryManager(30*time.Minute, 20)
+	defer m.Stop()
+	ctx := context.Background()
+
+	id, _ := m.Create(ctx, "user-1", models.DefaultConfig())
+
+	// 首条消息设置标题
+	m.AppendMessage(ctx, id, models.Message{Role: "user", Content: "第一条消息"})
+	// 第二条消息不应覆盖已有的标题
+	m.AppendMessage(ctx, id, models.Message{Role: "user", Content: "第二条消息"})
+
+	sess, _ := m.Get(ctx, id)
+	if sess.Title != "第一条消息" {
+		t.Errorf("Title = %q, want %q", sess.Title, "第一条消息")
+	}
+}
+
+func TestListByUser(t *testing.T) {
+	m := NewMemoryManager(30*time.Minute, 20)
+	defer m.Stop()
+	ctx := context.Background()
+
+	// 创建两个用户的不同会话
+	id1, _ := m.Create(ctx, "user-1", models.DefaultConfig())
+	m.AppendMessage(ctx, id1, models.Message{Role: "user", Content: "会话1"})
+	id2, _ := m.Create(ctx, "user-1", models.DefaultConfig())
+	m.AppendMessage(ctx, id2, models.Message{Role: "user", Content: "会话2"})
+	m.Create(ctx, "user-2", models.DefaultConfig()) // 其他用户的会话
+
+	list, total, err := m.ListByUser(ctx, "user-1", 1, 10)
+	if err != nil {
+		t.Fatalf("ListByUser: %v", err)
+	}
+	if total != 2 {
+		t.Errorf("total = %d, want 2", total)
+	}
+	if len(list) != 2 {
+		t.Fatalf("len = %d, want 2", len(list))
+	}
+	// 按 UpdatedAt 降序，id2 应在前
+	if list[0].ID != id2 {
+		t.Errorf("list[0].ID = %q, want %q", list[0].ID, id2)
+	}
+	if list[0].Title != "会话2" {
+		t.Errorf("list[0].Title = %q, want %q", list[0].Title, "会话2")
+	}
+	if list[0].LastMessage != "会话2" {
+		t.Errorf("list[0].LastMessage = %q, want %q", list[0].LastMessage, "会话2")
+	}
+}
+
+func TestListByUserPagination(t *testing.T) {
+	m := NewMemoryManager(30*time.Minute, 20)
+	defer m.Stop()
+	ctx := context.Background()
+
+	// 创建 5 个会话
+	for i := 0; i < 5; i++ {
+		id, _ := m.Create(ctx, "user-1", models.DefaultConfig())
+		m.AppendMessage(ctx, id, models.Message{Role: "user", Content: "msg"})
+	}
+
+	// 第 1 页，每页 2 条
+	list, total, _ := m.ListByUser(ctx, "user-1", 1, 2)
+	if total != 5 {
+		t.Errorf("total = %d, want 5", total)
+	}
+	if len(list) != 2 {
+		t.Errorf("page 1 len = %d, want 2", len(list))
+	}
+
+	// 第 2 页
+	list, _, _ = m.ListByUser(ctx, "user-1", 2, 2)
+	if len(list) != 2 {
+		t.Errorf("page 2 len = %d, want 2", len(list))
+	}
+
+	// 第 3 页（最后一页）
+	list, _, _ = m.ListByUser(ctx, "user-1", 3, 2)
+	if len(list) != 1 {
+		t.Errorf("page 3 len = %d, want 1", len(list))
+	}
+
+	// 超出范围的页
+	list, _, _ = m.ListByUser(ctx, "user-1", 10, 2)
+	if len(list) != 0 {
+		t.Errorf("out of range page len = %d, want 0", len(list))
+	}
+}
+
+func TestListByUserEmpty(t *testing.T) {
+	m := NewMemoryManager(30*time.Minute, 20)
+	defer m.Stop()
+	ctx := context.Background()
+
+	list, total, err := m.ListByUser(ctx, "no-such-user", 1, 10)
+	if err != nil {
+		t.Fatalf("ListByUser: %v", err)
+	}
+	if total != 0 {
+		t.Errorf("total = %d, want 0", total)
+	}
+	if len(list) != 0 {
+		t.Errorf("len = %d, want 0", len(list))
+	}
+}