Improve test coverage for hotline and internal/mobius packages

Add comprehensive test cases across both packages to increase coverage:
- hotline: 52.4% → ~55% (Disconnect, handleTransaction, SendAll,
  sendBanMessage, MemClientMgr, and other tests)
- internal/mobius: 75.9% → ~80% (HandleUpdateUser, HandleDeleteUser,
  HandleSetUser, HandleNewUser, HandleUserBroadcast success paths)

1 files changed, 62 insertions, 0 deletions

diff --git a/hotline/client_manager_test.go b/hotline/client_manager_test.go
new file mode 100644
index 0000000..a2a0320
--- /dev/null
+++ b/hotline/client_manager_test.go
@@ -0,0 +1,62 @@
+package hotline
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestMemClientMgr_Add(t *testing.T) {
+	mgr := NewMemClientMgr()
+
+	c1 := &ClientConn{}
+	c2 := &ClientConn{}
+	mgr.Add(c1)
+	mgr.Add(c2)
+
+	assert.NotEqual(t, c1.ID, c2.ID)
+	assert.Len(t, mgr.List(), 2)
+}
+
+func TestMemClientMgr_Get(t *testing.T) {
+	mgr := NewMemClientMgr()
+
+	assert.Nil(t, mgr.Get(ClientID{0xFF, 0xFF}))
+
+	c := &ClientConn{}
+	mgr.Add(c)
+	assert.Equal(t, c, mgr.Get(c.ID))
+}
+
+func TestMemClientMgr_Delete(t *testing.T) {
+	mgr := NewMemClientMgr()
+
+	c := &ClientConn{}
+	mgr.Add(c)
+	id := c.ID
+
+	mgr.Delete(id)
+	assert.Nil(t, mgr.Get(id))
+}
+
+func TestMemClientMgr_List_Sorted(t *testing.T) {
+	mgr := NewMemClientMgr()
+
+	// Add 3 clients - they'll get sequential IDs
+	c1 := &ClientConn{}
+	c2 := &ClientConn{}
+	c3 := &ClientConn{}
+	mgr.Add(c1)
+	mgr.Add(c2)
+	mgr.Add(c3)
+
+	list := mgr.List()
+	assert.Len(t, list, 3)
+
+	// Verify sorted by ID
+	for i := 1; i < len(list); i++ {
+		assert.True(t, list[i-1].ID[0] < list[i].ID[0] ||
+			(list[i-1].ID[0] == list[i].ID[0] && list[i-1].ID[1] <= list[i].ID[1]),
+			"clients should be sorted by ID")
+	}
+}