fix(handlers): fix softlock on forge purchases and N-points

MSG_CA_EXCHANGE_ITEM and MSG_MHF_USE_UD_SHOP_COIN had Parse() returning
"NOT IMPLEMENTED". The dispatch loop in handlePacketGroup treats any
Parse error as a silent drop — no ACK is sent, causing the client to
wait indefinitely (softlock). Reported on 9.3.0-rc1 for forge item
purchases and Hunting Road N-point interactions.

Fix follows the pattern from d27da5e: parse only the AckHandle, return
nil from Parse, and respond with doAckBufFail so the client's error
branch exits cleanly without reading response fields.

server/channelserver/handlers_misc.go

@@ -215,7 +215,13 @@ func handleMsgMhfGetUdShopCoin(s *Session, p mhfpacket.MHFPacket) {
 	doAckSimpleSucceed(s, pkt.AckHandle, bf.Data())
 }
 
-func handleMsgMhfUseUdShopCoin(s *Session, p mhfpacket.MHFPacket) {} // stub: unimplemented
+func handleMsgMhfUseUdShopCoin(s *Session, p mhfpacket.MHFPacket) {
+	pkt := p.(*mhfpacket.MsgMhfUseUdShopCoin)
+	// TODO: full response format is not yet reverse-engineered.
+	// doAckBufFail sends a well-formed buf-type ACK with error code 1.
+	// The client's fail branch exits cleanly without reading response fields.
+	doAckBufFail(s, pkt.AckHandle, nil)
+}
 
 func handleMsgMhfGetEnhancedMinidata(s *Session, p mhfpacket.MHFPacket) {
 	pkt := p.(*mhfpacket.MsgMhfGetEnhancedMinidata)

server/channelserver/handlers_misc_test.go

@@ -526,13 +526,8 @@ func TestHandleMsgMhfUseUdShopCoin(t *testing.T) {
 	server := createMockServer()
 	session := createMockSession(1, server)
 
-	defer func() {
-		if r := recover(); r != nil {
-			t.Errorf("handleMsgMhfUseUdShopCoin panicked: %v", r)
-		}
-	}()
-
-	handleMsgMhfUseUdShopCoin(session, nil)
+	pkt := &mhfpacket.MsgMhfUseUdShopCoin{AckHandle: 1}
+	handleMsgMhfUseUdShopCoin(session, pkt)
 }
 
 func TestHandleMsgMhfGetLobbyCrowd(t *testing.T) {
@@ -1028,7 +1023,6 @@ func TestEmptyHandlers_MiscFiles_Misc(t *testing.T) {
 		fn   func()
 	}{
 
-		{"handleMsgMhfUseUdShopCoin", func() { handleMsgMhfUseUdShopCoin(session, nil) }},
 		{"handleMsgMhfGetDailyMissionMaster", func() { handleMsgMhfGetDailyMissionMaster(session, nil) }},
 		{"handleMsgMhfGetDailyMissionPersonal", func() { handleMsgMhfGetDailyMissionPersonal(session, nil) }},
 		{"handleMsgMhfSetDailyMissionPersonal", func() { handleMsgMhfSetDailyMissionPersonal(session, nil) }},

server/channelserver/handlers_session.go

@@ -752,7 +752,13 @@ func handleMsgMhfTransitMessage(s *Session, p mhfpacket.MHFPacket) {
 	doAckBufSucceed(s, pkt.AckHandle, resp.Data())
 }
 
-func handleMsgCaExchangeItem(s *Session, p mhfpacket.MHFPacket) {} // stub: unimplemented
+func handleMsgCaExchangeItem(s *Session, p mhfpacket.MHFPacket) {
+	pkt := p.(*mhfpacket.MsgCaExchangeItem)
+	// TODO: full response format is not yet reverse-engineered.
+	// doAckBufFail sends a well-formed buf-type ACK with error code 1.
+	// The client's fail branch exits cleanly without reading response fields.
+	doAckBufFail(s, pkt.AckHandle, nil)
+}
 
 func handleMsgMhfServerCommand(s *Session, p mhfpacket.MHFPacket) {} // stub: unimplemented
 

server/channelserver/handlers_session_test.go

@@ -559,13 +559,8 @@ func TestHandleMsgCaExchangeItem(t *testing.T) {
 	server := createMockServer()
 	session := createMockSession(1, server)
 
-	defer func() {
-		if r := recover(); r != nil {
-			t.Errorf("handleMsgCaExchangeItem panicked: %v", r)
-		}
-	}()
-
-	handleMsgCaExchangeItem(session, nil)
+	pkt := &mhfpacket.MsgCaExchangeItem{AckHandle: 1}
+	handleMsgCaExchangeItem(session, pkt)
 }
 
 func TestHandleMsgMhfServerCommand(t *testing.T) {
@@ -1068,7 +1063,6 @@ func TestEmptyHandlers_HandlersGo(t *testing.T) {
 		{"handleMsgSysUpdateRight", func() { handleMsgSysUpdateRight(session, nil) }},
 		{"handleMsgSysAuthQuery", func() { handleMsgSysAuthQuery(session, nil) }},
 		{"handleMsgSysAuthTerminal", func() { handleMsgSysAuthTerminal(session, nil) }},
-		{"handleMsgCaExchangeItem", func() { handleMsgCaExchangeItem(session, nil) }},
 		{"handleMsgMhfServerCommand", func() { handleMsgMhfServerCommand(session, nil) }},
 		{"handleMsgMhfSetLoginwindow", func() { handleMsgMhfSetLoginwindow(session, nil) }},
 		{"handleMsgSysTransBinary", func() { handleMsgSysTransBinary(session, nil) }},
@@ -1106,7 +1100,6 @@ func TestEmptyHandlers_Concurrent(t *testing.T) {
 		handleMsgSysUpdateRight,
 		handleMsgSysAuthQuery,
 		handleMsgSysAuthTerminal,
-		handleMsgCaExchangeItem,
 		handleMsgMhfServerCommand,
 		handleMsgMhfSetLoginwindow,
 		handleMsgSysTransBinary,

server/channelserver/handlers_simple_test.go

@@ -279,7 +279,6 @@ func TestEmptyHandlers_NoDb(t *testing.T) {
 		{"handleMsgSysUpdateRight", handleMsgSysUpdateRight},
 		{"handleMsgSysAuthQuery", handleMsgSysAuthQuery},
 		{"handleMsgSysAuthTerminal", handleMsgSysAuthTerminal},
-		{"handleMsgCaExchangeItem", handleMsgCaExchangeItem},
 		{"handleMsgMhfServerCommand", handleMsgMhfServerCommand},
 		{"handleMsgMhfSetLoginwindow", handleMsgMhfSetLoginwindow},
 		{"handleMsgSysTransBinary", handleMsgSysTransBinary},
@@ -294,7 +293,6 @@ func TestEmptyHandlers_NoDb(t *testing.T) {
 		{"handleMsgMhfKickExportForce", handleMsgMhfKickExportForce},
 		{"handleMsgSysSetStatus", handleMsgSysSetStatus},
 		{"handleMsgSysEcho", handleMsgSysEcho},
-		{"handleMsgMhfUseUdShopCoin", handleMsgMhfUseUdShopCoin},
 		{"handleMsgMhfEnterTournamentQuest", handleMsgMhfEnterTournamentQuest},
 	}