# Task 3 Brief: TCM command builders

## Context

Tasks 1 and 2 are complete. Existing TCM frame codec is in src/core/tcm_frame.* and C ABI frame utilities are in src/c_api.cpp.

CMake is unavailable on PATH in this environment. Keep CMakeLists.txt correct, but use direct MinGW g++ verification if CMake cannot run.

## Global constraints

- Use only original source code; do not link proprietary SDK binaries.
- Current workspace is not a git repository; replace commit steps with verification plus updates to progress.md.
- Keep public C ABI free of C++ types.
- Use C++17.
- libusb-1.0 is the only native runtime dependency for the core library.
- Firmware update commands are not exposed as an easy accidental CLI action.
- IR protocol gaps return MAG160C_ERR_PROTOCOL_UNKNOWN or MAG160C_ERR_UNSUPPORTED.

## Files

- Create: src/core/transport.hpp
- Create: src/core/tcm_device.hpp
- Create: src/core/tcm_device.cpp
- Create: tests/cpp/test_tcm_device.cpp
- Modify: CMakeLists.txt
- Modify: include/mag160c/mag160c.h
- Modify: src/c_api.cpp
- Update: progress.md with the checkpoint.

## Interfaces to produce

- mag160c::core::Transport
- mag160c::core::TcmCommandBuilder
- mag160c_tcm_build_rotate_frame
- mag160c_tcm_build_light_frame

## Required transport interface

```cpp
class Transport {
public:
    virtual ~Transport() = default;
    virtual mag160c_error_t write(const std::vector<uint8_t>& bytes) = 0;
    virtual mag160c_error_t read(std::vector<uint8_t>* out, int timeout_ms) = 0;
};
```

## Required TCM command behavior

- Frame id starts at 1.
- Frame id increments after each encoded frame.
- Frame id wraps to 1 before reaching 0x8000.
- rotate clamps input to [-128, 128].
- rotate payload is [direction, magnitude], direction 0 for positive and 1 for negative.
- light payload is [on, red, green, blue].
- red/green/blue/yellow channel value is 0xff.
- off payload is [0, 0, 0, 0].
- light steady sub is 0x31, blink is 0x32, breath is 0x33.
- all observed TCM main commands here use main 0x02.

## Required exact test vectors

- rotate +5 with initial frame id 1:

```text
7e 00 07 85 02 77 00 01 00 05 7f
```

- after one prior command, rotate -3 with frame id 2:

```text
7e 00 07 85 02 77 00 02 01 03 7f
```

- green blink with initial frame id 1:

```text
7e 00 09 87 02 32 00 01 01 00 ff 00 35
```

## Required C ABI declarations

Add to include/mag160c/mag160c.h:

```c
typedef enum mag160c_tcm_light_color_t {
    MAG160C_TCM_LIGHT_OFF = 0,
    MAG160C_TCM_LIGHT_RED = 1,
    MAG160C_TCM_LIGHT_GREEN = 2,
    MAG160C_TCM_LIGHT_BLUE = 3,
    MAG160C_TCM_LIGHT_YELLOW = 4
} mag160c_tcm_light_color_t;

typedef enum mag160c_tcm_light_mode_t {
    MAG160C_TCM_LIGHT_STEADY = 0,
    MAG160C_TCM_LIGHT_BLINK = 1,
    MAG160C_TCM_LIGHT_BREATH = 2
} mag160c_tcm_light_mode_t;

MAG160C_API mag160c_error_t mag160c_tcm_build_rotate_frame(
    int angle,
    uint8_t* out_bytes,
    size_t out_capacity,
    size_t* out_size
);

MAG160C_API mag160c_error_t mag160c_tcm_build_light_frame(
    mag160c_tcm_light_color_t color,
    mag160c_tcm_light_mode_t mode,
    uint8_t* out_bytes,
    size_t out_capacity,
    size_t* out_size
);
```

## Required C ABI behavior

- Build helpers are dry-run byte builders only; they do not talk to USB.
- If out_size is null, return MAG160C_ERR_INVALID_ARGUMENT.
- If output buffer is null or too small, set out_size to the required frame size and return MAG160C_ERR_INVALID_ARGUMENT.
- On success, copy bytes, set out_size, clear last_error, return MAG160C_OK.
- Invalid light color or mode returns MAG160C_ERR_INVALID_ARGUMENT and sets a useful last_error.

## Required tests

Create tests/cpp/test_tcm_device.cpp with:

- test_rotate_positive_payload exact vector.
- test_rotate_negative_payload_and_frame_increment exact vector.
- test_green_blink_payload exact vector.

Also extend tests/cpp/test_c_api.cpp if convenient to check the new dry-run C ABI for rotate +5.

## CMake update

- Add src/core/tcm_device.cpp to mag160c_core sources.
- Add test_tcm_device executable linked to mag160c_core.
- Give test_tcm_device access to src private headers.
- Register test_tcm_device with CTest.

## Verification

First try:

```powershell
cmake --build build
ctest --test-dir build --output-on-failure
```

If CMake is unavailable, run:

```powershell
g++ -std=c++17 -DMAG160C_STATIC -DMAG160C_HAS_LIBUSB=0 -Iinclude -Isrc src\core\error.cpp src\core\context.cpp src\core\tcm_frame.cpp src\core\tcm_device.cpp src\c_api.cpp tests\cpp\test_c_api.cpp -o build_task3_c_api_test.exe
.\build_task3_c_api_test.exe
g++ -std=c++17 -DMAG160C_STATIC -DMAG160C_HAS_LIBUSB=0 -Iinclude -Isrc src\core\error.cpp src\core\context.cpp src\core\tcm_frame.cpp src\core\tcm_device.cpp src\c_api.cpp tests\cpp\test_tcm_frame.cpp -o build_task3_tcm_frame_test.exe
.\build_task3_tcm_frame_test.exe
g++ -std=c++17 -DMAG160C_STATIC -DMAG160C_HAS_LIBUSB=0 -Iinclude -Isrc src\core\error.cpp src\core\context.cpp src\core\tcm_frame.cpp src\core\tcm_device.cpp src\c_api.cpp tests\cpp\test_tcm_device.cpp -o build_task3_tcm_device_test.exe
.\build_task3_tcm_device_test.exe
```

Expected: all executables exit 0.

## Progress checkpoint

Append this line to progress.md after verification:

```markdown
- Implemented Task 3 TCM command builder, dry-run C ABI helpers, and command payload tests.
```

## Report contract

Write a report to .superpowers/sdd/task-3-report.md with:

- status: DONE, DONE_WITH_CONCERNS, NEEDS_CONTEXT, or BLOCKED
- files created/modified
- exact commands run
- test results
- concerns, if any
- self-review notes