# Sprint Contract: Assembly Sparse Solver Path

## Objective
Rebuild or verify full-space assembly, reduced free-DOF solve path, solver adapter boundary, and full-vector reaction recovery using the rebuilt MITC4 kernel.

## Required Reading
- /AGENTS.md
- /docs/ARCHITECTURE.md
- /docs/ADR.md
- /docs/NUMERICAL_CONVENTIONS.md
- /docs/MITC4_FORMULATION.md

## Scope
- Assemble global stiffness and external load vectors.
- Preserve full-space data for `RF = K_full * U_full - F_full`.
- Apply constrained DOF elimination via `DofManager`.
- Use the current deterministic test solver or adapter boundary; keep MKL behind a future adapter.

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

## Explicit Non-Goals
- Do not expose MKL or TBB APIs directly in solver core.
- Do not compare stored Abaqus references yet.
- Do not compute reactions from reduced equations.

## Tests To Write First
- Small assembled system tests with known displacement.
- Full-vector `RF` recovery tests.
- Constrained/free projection tests through assembly.
- Singular solve diagnostic tests.
- Sparse pattern deterministic ordering tests if sparse structure exists.

## Reference Artifacts
- None.

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

## Evaluator Checklist
- Full-space stiffness/load/displacement are available or reconstructable for reactions.
- Solver adapter boundary is preserved.
- Singular failures remain actionable.

## Handoff Requirements
- Record assembly and reaction readiness in `PROGRESS.md`.

## Do Not
- Do not let elements own global equation ids.