feat(protbot): add headless MHF protocol bot as cmd/protbot

Copy MHBridge into the Erupe module as cmd/protbot/ so it can be
built, tested, and maintained alongside the server. The bot
implements the full sign → entrance → channel login flow and
supports lobby entry, chat, session setup, and quest enumeration.

The conn/ package keeps its own Blowfish crypto primitives to avoid
importing erupe-ce/config (which requires a config file at init).

cmd/protbot/scenario/chat.go

@@ -0,0 +1,74 @@
+package scenario
+
+import (
+	"fmt"
+
+	"erupe-ce/common/byteframe"
+	"erupe-ce/common/stringsupport"
+
+	"erupe-ce/cmd/protbot/protocol"
+)
+
+// ChatMessage holds a parsed incoming chat message.
+type ChatMessage struct {
+	ChatType   uint8
+	SenderName string
+	Message    string
+}
+
+// SendChat sends a chat message via MSG_SYS_CAST_BINARY with a MsgBinChat payload.
+// broadcastType controls delivery scope: 0x03 = stage, 0x06 = world.
+func SendChat(ch *protocol.ChannelConn, broadcastType, chatType uint8, message, senderName string) error {
+	payload := protocol.BuildChatPayload(chatType, message, senderName)
+	pkt := protocol.BuildCastBinaryPacket(broadcastType, 1, payload)
+	fmt.Printf("[chat] Sending chat (type=%d, broadcast=%d): %s\n", chatType, broadcastType, message)
+	return ch.SendPacket(pkt)
+}
+
+// ChatCallback is invoked when a chat message is received.
+type ChatCallback func(msg ChatMessage)
+
+// ListenChat registers a handler on MSG_SYS_CASTED_BINARY that parses chat
+// messages (messageType=1) and invokes the callback.
+func ListenChat(ch *protocol.ChannelConn, cb ChatCallback) {
+	ch.OnPacket(protocol.MSG_SYS_CASTED_BINARY, func(opcode uint16, data []byte) {
+		// MSG_SYS_CASTED_BINARY layout from server:
+		//   uint32 unk
+		//   uint8  broadcastType
+		//   uint8  messageType
+		//   uint16 dataSize
+		//   []byte payload
+		if len(data) < 8 {
+			return
+		}
+		messageType := data[5]
+		if messageType != 1 { // Only handle chat messages.
+			return
+		}
+		bf := byteframe.NewByteFrameFromBytes(data)
+		_ = bf.ReadUint32() // unk
+		_ = bf.ReadUint8()  // broadcastType
+		_ = bf.ReadUint8()  // messageType
+		dataSize := bf.ReadUint16()
+		if dataSize == 0 {
+			return
+		}
+		payload := bf.ReadBytes(uint(dataSize))
+
+		// Parse MsgBinChat inner payload.
+		pbf := byteframe.NewByteFrameFromBytes(payload)
+		_ = pbf.ReadUint8()  // unk0
+		chatType := pbf.ReadUint8()
+		_ = pbf.ReadUint16() // flags
+		_ = pbf.ReadUint16() // senderNameLen
+		_ = pbf.ReadUint16() // messageLen
+		msg := stringsupport.SJISToUTF8(pbf.ReadNullTerminatedBytes())
+		sender := stringsupport.SJISToUTF8(pbf.ReadNullTerminatedBytes())
+
+		cb(ChatMessage{
+			ChatType:   chatType,
+			SenderName: sender,
+			Message:    msg,
+		})
+	})
+}