diff --git a/KeyBorad/KeyBorad/COM/Com_ProtoCodec.cpp b/KeyBorad/KeyBorad/COM/Com_ProtoCodec.cpp
new file mode 100644
index 0000000..35a456c
--- /dev/null
+++ b/KeyBorad/KeyBorad/COM/Com_ProtoCodec.cpp
@@ -0,0 +1,59 @@
+#include "COM/Com_ProtoCodec.h"
+
+#include "COM/Com_CdcDecode.h"
+#include "COM/Com_CdcEncode.h"
+
+namespace
+{
+
+quint16 Com_Func_ReadLe16(const QByteArray& ByteArray, int Offset)
+{
+    return static_cast<quint16>(
+        static_cast<quint8>(ByteArray.at(Offset)) |
+        (static_cast<quint16>(static_cast<quint8>(ByteArray.at(Offset + 1))) << 8));
+}
+
+} // namespace
+
+bool Com_ProtoCodec_ParseFrame(const QByteArray& ByteArray, Packet* p_Packet)
+{
+    return Com_Cdc_Func_ParseFrame(ByteArray, p_Packet);
+}
+
+bool Com_ProtoCodec_TryTakeFrame(QByteArray* p_Buffer, Packet* p_Packet)
+{
+    return Com_Cdc_Func_TryTakeFrame(p_Buffer, p_Packet);
+}
+
+QByteArray Com_ProtoCodec_BuildHelloReq()
+{
+    const Packet_HelloReq HelloReq;
+    return Com_Cdc_Func_BuildHelloReq(HelloReq);
+}
+
+bool Com_ProtoCodec_IsHelloRsp(const Packet& PacketData)
+{
+    return (PacketData.type == Com_Type_HelloRsp) &&
+        (PacketData.data.size() == Packet_len::Com_Len_HelloRsp);
+}
+
+bool Com_ProtoCodec_ParseHelloRsp(
+    const Packet& PacketData,
+    Packet_HelloRsp* p_HelloRsp)
+{
+    if ((p_HelloRsp == nullptr) || !Com_ProtoCodec_IsHelloRsp(PacketData))
+    {
+        return false;
+    }
+
+    Packet_HelloRsp HelloRsp;
+    HelloRsp.ProtocolVersion = static_cast<quint8>(PacketData.data.at(0));
+    HelloRsp.VendorId = Com_Func_ReadLe16(PacketData.data, 1);
+    HelloRsp.ProductId = Com_Func_ReadLe16(PacketData.data, 3);
+    HelloRsp.FirmwareMajor = static_cast<quint8>(PacketData.data.at(5));
+    HelloRsp.FirmwareMinor = static_cast<quint8>(PacketData.data.at(6));
+    HelloRsp.CapabilityFlags = Com_Func_ReadLe16(PacketData.data, 7);
+
+    *p_HelloRsp = HelloRsp;
+    return true;
+}
diff --git a/KeyBorad/KeyBorad/COM/Com_ProtoCodec.h b/KeyBorad/KeyBorad/COM/Com_ProtoCodec.h
new file mode 100644
index 0000000..a99e140
--- /dev/null
+++ b/KeyBorad/KeyBorad/COM/Com_ProtoCodec.h
@@ -0,0 +1,14 @@
+#pragma once
+
+#include <QtCore/QByteArray>
+
+#include "COM/Com_Cdc.h"
+
+bool Com_ProtoCodec_ParseFrame(const QByteArray& ByteArray, Packet* p_Packet);
+bool Com_ProtoCodec_TryTakeFrame(QByteArray* p_Buffer, Packet* p_Packet);
+
+QByteArray Com_ProtoCodec_BuildHelloReq();
+bool Com_ProtoCodec_IsHelloRsp(const Packet& PacketData);
+bool Com_ProtoCodec_ParseHelloRsp(
+    const Packet& PacketData,
+    Packet_HelloRsp* p_HelloRsp);
diff --git a/KeyBorad/KeyBorad/KeyBorad.vcxproj b/KeyBorad/KeyBorad/KeyBorad.vcxproj
index 8ab9680..0aa0a86 100644
--- a/KeyBorad/KeyBorad/KeyBorad.vcxproj
+++ b/KeyBorad/KeyBorad/KeyBorad.vcxproj
@@ -96,6 +96,8 @@
   <ItemGroup>
     <ClInclude Include="APP\AppTheme.h" />
     <ClInclude Include="COM\Com_Cdc.h" />
+    <ClCompile Include="COM\Com_ProtoCodec.cpp" />
+    <ClInclude Include="COM\Com_ProtoCodec.h" />
     <ClCompile Include="COM\Com_CdcEncode.cpp" />
     <ClInclude Include="COM\Com_CdcEncode.h" />
     <ClCompile Include="COM\Com_CdcDecode.cpp" />
diff --git a/KeyBorad/KeyBorad/KeyBorad.vcxproj.filters b/KeyBorad/KeyBorad/KeyBorad.vcxproj.filters
index 4a8ba16..fbe6f25 100644
--- a/KeyBorad/KeyBorad/KeyBorad.vcxproj.filters
+++ b/KeyBorad/KeyBorad/KeyBorad.vcxproj.filters
@@ -29,6 +29,12 @@
     <ClInclude Include="COM\Com_Cdc.h">
       <Filter>Header Files</Filter>
     </ClInclude>
+    <ClCompile Include="COM\Com_ProtoCodec.cpp">
+      <Filter>Source Files</Filter>
+    </ClCompile>
+    <ClInclude Include="COM\Com_ProtoCodec.h">
+      <Filter>Header Files</Filter>
+    </ClInclude>
     <ClCompile Include="COM\Com_CdcEncode.cpp">
       <Filter>Source Files</Filter>
     </ClCompile>
diff --git a/docs/host_com_rebuild.md b/docs/host_com_rebuild.md
new file mode 100644
index 0000000..88161a4
--- /dev/null
+++ b/docs/host_com_rebuild.md
@@ -0,0 +1,58 @@
+# Host COM Rebuild
+
+## Goal
+
+Keep the protocol layer small and explicit.
+
+The COM layer should:
+
+- define packet-facing helpers
+- own frame parsing and packet building
+- avoid transport concerns
+- avoid UI and session concerns
+
+## Completed Nodes
+
+### Node 1: legacy protocol baseline
+
+Files already present before this step:
+
+- `KeyBorad/KeyBorad/COM/Com_Cdc.h`
+- `KeyBorad/KeyBorad/COM/Com_CdcEncode.h`
+- `KeyBorad/KeyBorad/COM/Com_CdcEncode.cpp`
+- `KeyBorad/KeyBorad/COM/Com_CdcDecode.h`
+- `KeyBorad/KeyBorad/COM/Com_CdcDecode.cpp`
+
+Design notes:
+
+- these files preserve the old packet format
+- they already encode and decode complete CDC frames
+- they also contain per-packet payload helpers
+
+### Node 2: unified protocol entry
+
+Files added in this step:
+
+- `KeyBorad/KeyBorad/COM/Com_ProtoCodec.h`
+- `KeyBorad/KeyBorad/COM/Com_ProtoCodec.cpp`
+
+Design notes:
+
+- provides a thin and readable entry point for higher layers
+- keeps `DRI` from depending on packet parsing
+- keeps `LGC` from depending on low-level byte layout details
+- starts from the smallest useful handshake path
+
+Implemented behavior:
+
+- build `HelloReq` frame
+- validate whether a parsed packet is `HelloRsp`
+- decode `HelloRsp`
+- forward frame parsing and stream extraction to the existing low-level codec
+
+## Next COM nodes
+
+- bitmap encode/decode helper
+- ack/error helper
+- time sync and theme helper
+- replace direct `Com_Cdc*` calls in higher layers with `Com_ProtoCodec*`