# Step 8: domain-polymorphic-ownership

## Read First

Read these files before editing:

- `/AGENTS.md`
- `/docs/AGENT_RULES.md`
- `/docs/ARCHITECTURE.md`
- `/docs/implementation-plans/analysis-model-objects-implementation-plan.md`
- `/include/fesa/core/Domain.hpp`
- all model object headers created by previous steps

## Task

Extend `Domain` with RAII ownership APIs for polymorphic model objects while preserving existing definition-storage tests.

Allowed files:

- Modify `/include/fesa/core/Domain.hpp`
- Modify `/src/core/Domain.cpp`
- Create `/tests/core/domain_model_object_test.cpp`
- Modify `/tests/core/domain_bootstrap_test.cpp`
- Modify `/CMakeLists.txt`

Required behavior:

- `Domain::addElementObject(std::unique_ptr<Element>)`
- `Domain::findElementObject(ElementId)` and `Domain::elementObject(ElementId)`
- equivalent add/find/direct APIs for `Material`, `Load`, and model `BoundaryCondition`.
- duplicate ids or duplicate load/boundary keys throw `std::invalid_argument`.
- missing direct lookup throws `std::out_of_range`.
- retrieval returns const base references or const base pointers.
- existing `Definition` APIs remain available.

## Tests To Write First

Write `/tests/core/domain_model_object_test.cpp` before production changes:

- Domain owns `Mitc4Element`, `LinearElasticMaterial`, `NodalLoad`, and `SinglePointConstraint` through `std::unique_ptr`.
- Find/direct lookup through base APIs works.
- Duplicate ids throw for element/material.
- Missing direct lookup throws.

Run targeted build and confirm RED.

## Acceptance Criteria

Run:

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

Update step 8 status.

## Do Not

- Do not remove existing definition APIs in this step.
- Do not add solver state to Domain.