# Step 5: property-section-model

## 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/PropertyDefinition.hpp`

## Task

Add shell property/section model object.

Allowed files:

- Create `/include/fesa/property/ShellProperty.hpp`
- Create `/src/property/ShellProperty.cpp`
- Create `/tests/property/shell_property_test.cpp`
- Modify `/CMakeLists.txt`

Required behavior:

- Stores property id, material id, and thickness.
- Exposes const accessors.
- Rejects non-positive thickness with `std::invalid_argument`.
- Does not compute shell section stiffness.

## Tests To Write First

Write `/tests/property/shell_property_test.cpp` before production changes:

- Valid property stores id/material/thickness.
- Zero or negative thickness 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
```

Update step 5 status.

## Do Not

- Do not implement membrane, bending, or shear constitutive stiffness.