test: expand channelserver coverage from 20% to 25%

Add tests for:
- Discord handlers (getPlayerSlice, getCharacterList)
- House handlers (boxToBytes, HouseData, Title structs)
- Mail struct tests
- Mercenary handlers (Partner, HunterNavi structs)
- Shop/Gacha handlers (writeShopItems, ShopItem, Gacha structs)
- Additional handler coverage for guild, tower, and simple handlers
- Stage handler tests for binary operations and enumeration
- Channel server tests for BroadcastMHF and session management

server/channelserver/handlers_discord_test.go

@@ -0,0 +1,163 @@
+package channelserver
+
+import (
+	"testing"
+)
+
+func TestPlayerStruct(t *testing.T) {
+	player := Player{
+		CharName: "TestPlayer",
+		QuestID:  5,
+	}
+
+	if player.CharName != "TestPlayer" {
+		t.Errorf("CharName = %s, want TestPlayer", player.CharName)
+	}
+	if player.QuestID != 5 {
+		t.Errorf("QuestID = %d, want 5", player.QuestID)
+	}
+}
+
+func TestGetPlayerSlice_EmptyServer(t *testing.T) {
+	server := createMockServer()
+	server.Channels = []*Server{}
+
+	players := getPlayerSlice(server)
+
+	if len(players) != 0 {
+		t.Errorf("Expected 0 players, got %d", len(players))
+	}
+}
+
+func TestGetPlayerSlice_WithChannel(t *testing.T) {
+	server := createMockServer()
+
+	// Create a channel with stages
+	channel := &Server{
+		stages: make(map[string]*Stage),
+	}
+
+	// Create a stage with clients
+	stage := NewStage("test_stage")
+	session := createMockSession(1, server)
+	session.Name = "Player1"
+	stage.clients[session] = session.charID
+
+	channel.stages["test_stage"] = stage
+	server.Channels = []*Server{channel}
+
+	players := getPlayerSlice(server)
+
+	if len(players) != 1 {
+		t.Errorf("Expected 1 player, got %d", len(players))
+	}
+	if len(players) > 0 && players[0].CharName != "Player1" {
+		t.Errorf("Expected CharName Player1, got %s", players[0].CharName)
+	}
+}
+
+func TestGetPlayerSlice_MultiplePlayersMultipleStages(t *testing.T) {
+	server := createMockServer()
+
+	channel := &Server{
+		stages: make(map[string]*Stage),
+	}
+
+	// Stage 1 with one player
+	stage1 := NewStage("stage1")
+	session1 := createMockSession(1, server)
+	session1.Name = "Player1"
+	stage1.clients[session1] = session1.charID
+	channel.stages["stage1"] = stage1
+
+	// Stage 2 with two players
+	stage2 := NewStage("stage2")
+	session2 := createMockSession(2, server)
+	session2.Name = "Player2"
+	session3 := createMockSession(3, server)
+	session3.Name = "Player3"
+	stage2.clients[session2] = session2.charID
+	stage2.clients[session3] = session3.charID
+	channel.stages["stage2"] = stage2
+
+	server.Channels = []*Server{channel}
+
+	players := getPlayerSlice(server)
+
+	if len(players) != 3 {
+		t.Errorf("Expected 3 players, got %d", len(players))
+	}
+}
+
+func TestGetPlayerSlice_EmptyStage(t *testing.T) {
+	server := createMockServer()
+
+	channel := &Server{
+		stages: make(map[string]*Stage),
+	}
+
+	// Empty stage (no clients)
+	emptyStage := NewStage("empty_stage")
+	channel.stages["empty_stage"] = emptyStage
+
+	server.Channels = []*Server{channel}
+
+	players := getPlayerSlice(server)
+
+	if len(players) != 0 {
+		t.Errorf("Expected 0 players from empty stage, got %d", len(players))
+	}
+}
+
+func TestGetCharacterList_EmptyServer(t *testing.T) {
+	server := createMockServer()
+	server.Channels = []*Server{}
+
+	result := getCharacterList(server)
+
+	expected := "===== Online: 0 =====\n"
+	if result != expected {
+		t.Errorf("Expected %q, got %q", expected, result)
+	}
+}
+
+func TestGetCharacterList_WithPlayers(t *testing.T) {
+	server := createMockServer()
+
+	channel := &Server{
+		stages: make(map[string]*Stage),
+	}
+
+	stage := NewStage("lobby")
+	session := createMockSession(1, server)
+	session.Name = "Hunter1"
+	stage.clients[session] = session.charID
+	channel.stages["lobby"] = stage
+
+	server.Channels = []*Server{channel}
+
+	result := getCharacterList(server)
+
+	// Should contain the online count
+	if len(result) == 0 {
+		t.Error("Expected non-empty result")
+	}
+
+	// Should contain "Online: 1"
+	if !contains(result, "Online: 1") {
+		t.Errorf("Expected result to contain 'Online: 1', got %q", result)
+	}
+}
+
+func contains(s, substr string) bool {
+	return len(s) >= len(substr) && (s == substr || len(s) > 0 && containsAt(s, substr))
+}
+
+func containsAt(s, substr string) bool {
+	for i := 0; i <= len(s)-len(substr); i++ {
+		if s[i:i+len(substr)] == substr {
+			return true
+		}
+	}
+	return false
+}