KeyBoard_QT/docs/host_logic_rebuild.md

# Host LGC Rebuild

## Goal

Keep the logic layer small, readable, and teachable.

The logic layer should:

- own connection state
- own handshake state
- call DRI for bytes
- call COM for frame and packet parsing
- expose a small interface to APP

The logic layer should not:

- parse serial bytes by itself
- enumerate devices directly
- own widget code

## Completed Nodes

### Node 1: function executor shell

Files:

- `KeyBorad/KeyBorad/LOGIC/Lgc_FunctionExecutor.h`
- `KeyBorad/KeyBorad/LOGIC/Lgc_FunctionExecutor.cpp`

Design notes:

- keep function execution out of session code
- reserve one place for OS-specific actions
- keep the initial implementation small

### Node 2: state model

Files updated in this step:

- `KeyBorad/KeyBorad/LOGIC/Lgc_State.h`

Design notes:

- state is plain data
- connection text and last action text live here
- handshake result fields live here

### Node 3: session handshake path

Files completed in this step:

- `KeyBorad/KeyBorad/LOGIC/Lgc_Session.h`
- `KeyBorad/KeyBorad/LOGIC/Lgc_Session.cpp`

Implemented behavior:

- try CDC handshake
- send `HelloReq`
- wait for `HelloRsp`
- store the active transport
- keep a stream buffer for CDC bytes
- return the next parsed packet to upper layers

### Node 4: core facade

Files completed in this step:

- `KeyBorad/KeyBorad/LOGIC/Lgc_Core.h`
- `KeyBorad/KeyBorad/LOGIC/Lgc_Core.cpp`

Implemented behavior:

- give APP one small entry point
- start CDC handshake through session
- expose `Start / Poll / Close / GetState`
- refresh state from `HelloRsp`
- update a simple action text when packets arrive