Remove legacy COM codec

docs/host_com_rebuild.md

@@ -20,69 +20,25 @@ The COM layer should not:
 
 ## Current file roles
 
-### `Com_Cdc.h`
+### `Com_PbCodec.h/.cpp`
 
-Owns the packet model:
+Owns the protobuf-side wrapper:
 
-- packet types
-- fixed payload lengths
-- payload structs
+- full protobuf frame serialize / parse
+- checksum validation
+- typed helper entry points like hello request / response
 
-### `Com_CdcEncode.h/.cpp`
+### `keyboard.pb.h/.cc`
 
-Owns the write direction:
+Own the generated protocol model:
 
-- checksum
-- full frame build
-- typed payload encode
-
-### `Com_CdcDecode.h/.cpp`
-
-Owns the read direction:
-
-- full frame parse
-- stream extraction
-- typed payload decode
+- outer `CdcFrame`
+- business `CdcPacketBody`
+- all message definitions
 
 ## Completed nodes
 
-### Node 1: legacy frame encode baseline
-
-Already present before this step:
-
-- build full frame
-- build all typed packets
-
-### Node 2: typed packet decode completion
-
-Files updated in this step:
-
-- `KeyBorad/KeyBorad/COM/Com_CdcDecode.h`
-- `KeyBorad/KeyBorad/COM/Com_CdcDecode.cpp`
-
-Design notes:
-
-- keep decode logic flat and explicit
-- one helper for little-endian reads
-- one helper for type + length validation
-- one decode function per packet type
-
-Implemented behavior:
-
-- parse frame header and checksum
-- extract frames from a byte stream
-- decode:
-  - `HelloReq`
-  - `HelloRsp`
-  - `Bitmap`
-  - `FunctionKeyEvent`
-  - `LedState`
-  - `TimeSync`
-  - `ThemeRgb`
-  - `Ack`
-  - `Error`
-
-### Node 3: protobuf thin wrapper
+### Node 1: protobuf thin wrapper
 
 Files added in this step:
 
@@ -102,16 +58,32 @@ Implemented behavior:
 - build `HelloReq` using generated protobuf types
 - parse `HelloRsp` using generated protobuf types
 
-Current limit:
+### Node 2: remove legacy manual codec
 
-- not wired into the project yet
-- protobuf runtime include and link setup is still pending
+Files removed in 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:
+
+- no dual path
+- no hand-written payload encode/decode path left behind
+- protobuf is now the only packet encode/decode direction
+
+Implemented behavior:
+
+- checksum moved into `Com_PbCodec.cpp`
+- old manual packet structs and old codec files removed
 
 ## COM done criteria
 
 For the current project stage, COM is considered done when:
 
-1. every supported packet can be built
-2. every supported packet can be parsed
-3. stream extraction is stable
-4. higher layers no longer need to know byte offsets
+1. the protocol source is the `.proto` file
+2. generated `.pb.*` files exist
+3. `Com_PbCodec` provides thin project-facing helpers
+4. no legacy hand-written packet codec remains