# Step 1: core-types-diagnostics

## Sprint Contract

### Objective
Add core numeric/id types, shell DOF enumeration, diagnostics primitives, and error-result conventions used by later layers.

### 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
- /phases/1-linear-static-mitc4/step0.md

### Scope
- Define int64-based ids, indices, and equation-number types.
- Define `double` as the default scalar precision.
- Define the six shell DOFs in the documented order: `UX`, `UY`, `UZ`, `RX`, `RY`, `RZ`.
- Add diagnostics/result primitives with enough context for parser, validation, and solver errors.

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

### Explicit Non-Goals
- Do not add Domain, parser, DofManager, sparse matrix, or MITC4 element behavior.
- Do not use 32-bit ids, equation numbers, or sparse indices.
- Do not encode global equation ids inside node or element data structures.

### Tests To Write First
- Unit tests for id/index/equation type sizes and signedness expectations.
- Unit tests for DOF ordering, component labels, and stable integer mapping.
- Unit tests for diagnostic severity, code, message, and source-location payloads.

### Reference Artifacts
- None.

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

### Evaluator Checklist
- Core types are reusable without depending on parser, analysis, MKL, TBB, or HDF5.
- DOF labels and order match `docs/NUMERICAL_CONVENTIONS.md`.
- Diagnostics can carry actionable context for unsupported input and singular systems.
- Tests were added before behavior and pass through validation.

### Handoff Requirements
- Record completed work and validation in `PROGRESS.md`.
- Keep `PLAN.md` focused on future blockers only.
- 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 explicit int64 and DOF-order assertions.

## Do Not
- Do not infer future element or solver APIs beyond what this contract requires.