# Sprint Contract: Stored Reference Regression

## Objective
Run automated stored-reference displacement regression against accepted Phase 1-compatible S4 cases, starting with the `quad_02` compatibility path chosen in step 1.

## Required Reading
- /AGENTS.md
- /docs/VERIFICATION_PLAN.md
- /docs/ABAQUS_INPUT_SUBSET.md
- /docs/RESULTS_SCHEMA.md
- /docs/MITC4_FORMULATION.md
- /references/

## Scope
- Wire accepted Phase 1-compatible reference inputs into automated tests.
- Compare FESA `U` against `*_displacements.csv` using documented tolerances.
- Keep original unsupported Abaqus files as provenance and negative/compatibility tests.
- Record pass/fail comparison details.

## Allowed Files
- `references/`
- `tests/`
- `include/`
- `src/` only for minimal fixes needed by reference regression
- `docs/VERIFICATION_PLAN.md`
- `PLAN.md`
- `PROGRESS.md`

## Explicit Non-Goals
- Do not require Abaqus execution.
- Do not accept `S4R`, `Part/Assembly/Instance`, `*Density`, or `NLGEOM=YES` through the parser without a prior parser contract.
- Do not mark Phase 1 complete with only one reference case unless `PLAN.md` records the remaining PRD gap.

## Tests To Write First
- Reference manifest or fixture discovery tests.
- `quad_02` accepted derivative input regression test if normalized in step 1.
- Original `quad_02.inp` unsupported-provenance test if parser scope still excludes `Part/Assembly/Instance`.
- CSV displacement comparison test with absolute and relative tolerances.

## Reference Artifacts
- `references/quad_02.inp`
- `references/quad_02_displacements.csv`
- Any normalized Phase 1-compatible derivative files from step 1.

## Acceptance Commands
```bash
python scripts/validate_workspace.py
```

## Evaluator Checklist
- Regression uses stored artifacts only.
- Original reference provenance is preserved.
- Comparison is node-id-based and reports errors clearly.
- Remaining PRD requirement for three stored references is recorded if not satisfied.

## Handoff Requirements
- Record reference pass/fail, tolerances, and residual risks in `PROGRESS.md`.
- Update `PLAN.md` with additional reference cases still needed.

## Do Not
- Do not tune solver formulas to one CSV without element-level tests remaining green.