# Step 0: requirements

## Read First

- `/AGENTS.md`
- `/docs/ABAQUS_SUBROUTINE_AGENT_DESIGN.md`
- `/docs/PRD.md`
- `/docs/ARCHITECTURE.md`
- `/docs/ADR.md`
- `/.codex/skills/abaqus-subroutine-requirements/SKILL.md`
- `/docs/requirements/README.md`

## Task

Create `/docs/requirements/uel-3d-euler-beam.md` for a 3D Euler-Bernoulli beam Abaqus/Standard `UEL`.

Use `feature_id = uel-3d-euler-beam`. Start from these harness-test assumptions and make any remaining uncertainty explicit as a requirement decision:

- Abaqus entry point: `UEL`.
- Element type: two-node, linear elastic, small-displacement 3D Euler-Bernoulli beam.
- Degrees of freedom: 12 total, 6 per node, ordered as `U1, U2, U3, UR1, UR2, UR3` at node 1 then node 2.
- Primary implementation target: static stiffness matrix `AMATRX` and internal force contribution `RHS`.
- Excluded from the first implementation unless requirements explicitly approve them: geometric nonlinearity, shear deformation, distributed loads, damping, mass matrix, thermal strain, warping torsion, plasticity, damage, and section offset.
- Material/section properties to decide in requirements: `E`, `G` or `nu`, `A`, `Iy`, `Iz`, `J`, element orientation definition, density if mass is later required.

The requirements document must include:

- Scope and non-scope.
- Must/should/could requirements.
- Requirement Verification Matrix with one verification method, acceptance criterion, and tolerance or decision owner for every must requirement.
- Required no-Abaqus evidence before Fortran production source changes.
- Required external Abaqus artifact evidence before solver-result comparison.
- Explicit decision list for unresolved physics or Abaqus keyword support.

Do not create Fortran source, tests, reference artifacts, or implementation plans in this step.

## Tests To Write First

- None. This is a requirements artifact step.

## Acceptance Criteria

```bash
python -m unittest discover -s scripts -p "test_*.py"
python scripts/validate_reference_artifacts.py
python scripts/validate_workspace.py
```

The step is complete only when `/docs/requirements/uel-3d-euler-beam.md` exists and every must requirement has measurable verification.

## Validation Notes

- Use externally generated ODB-extracted CSV artifacts for solver-result validation evidence.
- Do not require this repository to run Abaqus analyses.
- Update `/phases/uel-3d-euler-beam/index.json` step 0 with `completed`, `error`, or `blocked` and a concrete summary or reason.

## Forbidden

- Do not add JavaScript/TypeScript/npm fallback.
- Do not run Abaqus analyses from this project.
- Do not generate reference CSVs.
- Do not create Fortran production source.
- Do not break existing tests.