# Step 2: core-id-types

## Read First

Read these files before editing:

- `/AGENTS.md`
- `/docs/AGENT_RULES.md`
- `/docs/ADR.md`
- `/docs/ARCHITECTURE.md`
- `/docs/implementation-plans/domain-model-foundation-implementation-plan.md`
- `/CMakeLists.txt`
- `/tests/core/domain_bootstrap_test.cpp`

## Task

Introduce core id aliases and DOF ordering constants.

Allowed files:

- Create `/include/fesa/core/ModelTypes.hpp`
- Modify `/tests/core/domain_bootstrap_test.cpp` or create `/tests/core/model_types_test.cpp`
- Modify `/CMakeLists.txt` only to register the new test file if a separate test executable is created

Required API:

```cpp
namespace fesa::core {
using Id = std::int64_t;
using NodeId = Id;
using ElementId = Id;
using MaterialId = Id;
using PropertyId = Id;
using StepId = Id;

enum class Dof : std::uint8_t {
    U1 = 0,
    U2 = 1,
    U3 = 2,
    UR1 = 3,
    UR2 = 4,
    UR3 = 5
};

constexpr std::size_t kDofPerNode = 6;
}
```

## Tests To Write First

Write a failing C++ test that includes `fesa/core/ModelTypes.hpp` before creating the header.

The test must verify:

- `sizeof(fesa::core::Id) == 8`
- `kDofPerNode == 6`
- `Dof::U1` through `Dof::UR3` have ordinal values 0 through 5

Run the targeted CTest and verify it fails because the header is missing. Then implement the header.

## Acceptance Criteria

Run:

```powershell
cmake --build build/msvc-debug --config Debug
ctest --test-dir build/msvc-debug --output-on-failure -C Debug -R domain
python scripts/validate_workspace.py
```

Update `/phases/domain-model-foundation/index.json` step 2 with `completed`, `error`, or `blocked`.

## Do Not

- Do not add model storage in this step.
- Do not add equation numbering or solver state.