# Step 8: results-writer-minimal

## Sprint Contract

### Objective
Implement the minimal result model and writer boundary for Phase 1 `U` and `RF` step/frame/field outputs.

### Required Reading
- /AGENTS.md
- /PROGRESS.md
- /PLAN.md
- /docs/README.md
- /docs/HARNESS_ENGINEERING.md
- /docs/ARCHITECTURE.md
- /docs/ADR.md
- /docs/NUMERICAL_CONVENTIONS.md
- /docs/RESULTS_SCHEMA.md
- /phases/1-linear-static-mitc4/step6.md
- /phases/1-linear-static-mitc4/step7.md

### Scope
- Add result data structures for model ids/connectivity plus step/frame/field outputs.
- Support mandatory Phase 1 fields `U` and `RF` with components `UX`, `UY`, `UZ`, `RX`, `RY`, `RZ`.
- Add an in-memory or file-backed writer boundary as appropriate for the current build system.
- If HDF5 is implemented now, keep HDF5 APIs behind an adapter/wrapper.

### Allowed Files
- `include/**`
- `src/**`
- `tests/**`
- `docs/RESULTS_SCHEMA.md` only for clarification of agreed schema details
- `PLAN.md`
- `PROGRESS.md`
- `phases/1-linear-static-mitc4/index.json`

### Explicit Non-Goals
- Do not add stress, strain, shell force, history, nonlinear frame, thermal, or composite outputs unless R-007 is resolved and docs are updated first.
- Do not write RF from reduced vectors only.
- Do not expose HDF5 APIs in solver core headers.

### Tests To Write First
- Schema tests for step/frame layout and mandatory field names.
- Component-label and ordering tests for `U` and `RF`.
- Model id/connectivity storage tests using int64 ids.
- Adapter-boundary tests if HDF5 is introduced.

### Reference Artifacts
- None for solver regression. This step only prepares output data consumed by later comparison.

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

### Evaluator Checklist
- Result layout follows `docs/RESULTS_SCHEMA.md`.
- `U` and `RF` have six components in the documented order.
- HDF5, if present, is isolated behind an adapter.
- No extra Phase 1 outputs were added without resolving R-007.

### Handoff Requirements
- Record result writer scope and validation in `PROGRESS.md`.
- Update `PLAN.md` if R-007 changes or output scope remains blocked.
- 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 schema and component ordering.

## Do Not
- Do not treat a file being created as proof that its schema matches the contract.