# Step 6: analysis-model-dof-manager

## Sprint Contract

### Objective
Implement `AnalysisModelBuilder` and `DofManager` for one active linear static step with six-DOF nodes, constrained/free mapping, equation numbering, sparse-pattern input, and full/reduced vector reconstruction.

### Required Reading
- /AGENTS.md
- /PROGRESS.md
- /PLAN.md
- /docs/README.md
- /docs/HARNESS_ENGINEERING.md
- /docs/PRD.md
- /docs/ARCHITECTURE.md
- /docs/ADR.md
- /docs/NUMERICAL_CONVENTIONS.md
- /phases/1-linear-static-mitc4/step5.md

### Scope
- Build an `AnalysisModel` active view from validated `Domain`.
- Assign six shell DOFs per active node in documented order.
- Apply fixed boundary conditions by constrained DOF elimination.
- Produce int64 equation numbers for free DOFs and mappings for constrained DOFs.
- Provide reconstruction helpers between reduced vectors and full vectors.

### Allowed Files
- `include/**`
- `src/**`
- `tests/**`
- `PLAN.md`
- `PROGRESS.md`
- `phases/1-linear-static-mitc4/index.json`

### Explicit Non-Goals
- Do not assemble element stiffness or loads.
- Do not store equation ids on Node or Element objects.
- Do not solve linear systems or write HDF5 results.

### Tests To Write First
- DOF numbering tests for simple models with all six components.
- Constrained/free partition tests for fixed boundary conditions.
- Reduced/full reconstruction tests including constrained values set to zero for Phase 1.
- Sparse-pattern input tests using active element connectivity without assembling values.

### Reference Artifacts
- None.

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

### Evaluator Checklist
- `DofManager` owns global equation numbering.
- ids, sparse indices, and equations remain int64-based.
- Fixed constraints are handled by elimination, not penalty.
- Reconstruction supports later full-vector `RF` recovery.

### Handoff Requirements
- Record DOF behavior, tests, and validation in `PROGRESS.md`.
- Update `PLAN.md` only for future work or resolved blockers.
- Update the matching phase index entry: use `completed` with a one-line `summary`, or `blocked` with `blocked_reason`, or `error` with `error_message`.

## Verification
1. Run the acceptance command.
2. Inspect tests for constrained/free and full/reduced mapping edge cases.

## Do Not
- Do not make constrained DOF elimination depend on reduced-only reaction recovery.