refactor: store runtime objects in domain

phases/domain-runtime-storage/step4.md

@@ -0,0 +1,47 @@
+# Step 4: legacy-definition-extraction
+
+## Read First
+
+Read these files before editing:
+
+- `/AGENTS.md`
+- `/docs/AGENT_RULES.md`
+- `/docs/implementation-plans/domain-runtime-storage-implementation-plan.md`
+- `/include/fesa/core/Domain.hpp`
+- `/src/core/Domain.cpp`
+- `/tests/core/domain_storage_test.cpp`
+- `/CMakeLists.txt`
+
+## Task
+
+Remove parser-definition DTO persistence from `Domain`.
+
+Rules:
+
+- `Domain` must no longer include or store:
+  - `fesa/core/BoundaryCondition.hpp`
+  - `fesa/core/ElementDefinition.hpp`
+  - `fesa/core/LoadDefinition.hpp`
+  - `fesa/core/MaterialDefinition.hpp`
+  - `fesa/core/PropertyDefinition.hpp`
+- `Domain` may still include `StepDefinition.hpp` until a runtime step object is designed.
+- Definition classes may remain in the repository and their focused tests may remain, but they must not be part of Domain storage or Domain public API.
+- Do not implement parser or factory behavior in this step.
+
+## Tests To Write First
+
+- Add or update a compile-time assertion in `/tests/core/domain_storage_test.cpp` or a dedicated domain API test proving Domain retrieval returns runtime types for elements, materials, properties, loads, and boundary conditions.
+
+## Acceptance Criteria
+
+```powershell
+python -m unittest discover -s scripts -p "test_*.py"
+python scripts/validate_workspace.py
+git diff --check
+```
+
+## Verification Notes
+
+1. Confirm no `Domain` method returns a definition DTO except `LinearStaticStepDefinition`.
+2. Confirm `include/fesa/element/Element.hpp` no longer includes `ElementDefinition.hpp`.
+3. Update `phases/domain-runtime-storage/index.json` for this step result.