# Sprint Contract: Validation Singular Diagnostics

## Objective
Strengthen domain and analysis-model validation so invalid inputs and singular-prone models fail before or during solve with actionable diagnostics.

## Required Reading
- /AGENTS.md
- /docs/ARCHITECTURE.md
- /docs/NUMERICAL_CONVENTIONS.md
- /docs/ABAQUS_INPUT_SUBSET.md
- /docs/VERIFICATION_PLAN.md

## Scope
- Validate missing nodes, properties, materials, sets, boundary targets, load targets, active elements, and non-positive thickness.
- Add singular-prone diagnostics for no free DOFs, untouched free DOFs, missing loads where expected, and unconstrained drilling/rotational risks.
- Keep mesh quality diagnostics out of Phase 1.

## Allowed Files
- `include/`
- `src/`
- `tests/`
- `PLAN.md`
- `PROGRESS.md`

## Explicit Non-Goals
- Do not implement mesh quality metrics such as aspect ratio, skew, or warpage.
- Do not solve the global system in this step.
- Do not hide singular checks in element kernels.

## Tests To Write First
- Missing node/property/material diagnostics.
- Missing set used by shell section, boundary, or load.
- No active elements.
- No free DOFs.
- Free DOFs untouched by any active element connectivity.
- Rotational/drilling weak-constraint diagnostic smoke test.

## Reference Artifacts
- Negative inline test inputs may be used.

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

## Evaluator Checklist
- Diagnostics include node id, element id, property id, material id, set name, DOF component, and source line where available.
- Mesh quality remains explicitly deferred.
- Validation does not mutate `Domain`.

## Handoff Requirements
- Record validation coverage in `PROGRESS.md`.
- Note any remaining singular-diagnostic gaps in `PLAN.md`.

## Do Not
- Do not classify poor element shape as a Phase 1 mesh quality failure.