# Step 3: sets-and-section-properties

## Read First

Read these files before editing:

- `/AGENTS.md`
- `/docs/ARCHITECTURE.md`
- `/docs/ADR.md`
- `/docs/io-definitions/abaqus-input-parser-io.md`
- `/src/fesa/model/domain.hpp`
- `/src/fesa/model/element.hpp`
- `/src/fesa/model/property.hpp`
- `/src/fesa/io/abaqus/input_parser.hpp`
- `/src/fesa/io/abaqus/input_parser.cpp`

Review completed parser tests and phase summaries first.

## Task

Extend the model and parser only as needed to represent set membership and
section-to-property assignment for V0 bar/truss models.

Required behavior:

- Parse `*NSET, NSET=<name>` node membership rows.
- Parse `*ELSET, ELSET=<name>` element membership rows.
- Parse one V0 section keyword that assigns a material name to an element set.
  Prefer the smallest section subset compatible with the current V0 element
  path.
- Preserve deterministic member ordering as read, unless the I/O contract
  explicitly states otherwise.
- Keep `Domain` as the owner of model definition data. Do not store equation ids
  on nodes or elements.

## Tests To Write First

Add focused C++ tests before production code:

- a model test for any new set/section semantic model API;
- a parser test proving `*NSET`, `*ELSET`, and the selected section keyword map
  into the semantic model.

Run targeted CTest and confirm the tests fail before implementation.

## Acceptance Criteria

```powershell
ctest --test-dir build/msvc-debug --output-on-failure -C Debug -R "(model_|abaqus_input_parser_)"
python -m unittest discover -s scripts -p "test_*.py"
python scripts/validate_workspace.py
```

## Verification Procedure

Update step 3 status with summary or a concrete error/blocked reason.

## Forbidden

- Do not parse materials beyond names needed for section linkage.
- Do not add loads, boundary conditions, or analysis steps.
- Do not generate or modify reference artifacts.