# 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*`