## Summary

<!-- What does this PR change and why? -->

## Type of change

- [ ] Bug fix
- [ ] New feature
- [ ] Docs only
- [ ] Refactor (no intended behavior change)

## Risk / impact

- [ ] Touches solver numerics (`solver-c`)
- [ ] Touches API contract (`solver-api`)
- [ ] Touches GUI (`gui-ts`)
- [ ] Updates goldens / deterministic hashes

## Testing

```bash
make test
```

Paste output or note what could not be run.

## Documentation

- [ ] Updated `Agents/MATH_SPEC.md` (if equations/BCs changed)
- [ ] Updated `Agents/COMPUTE_PLAN.md` (if roadmap/gaps changed)
- [ ] Updated `README.md` / `docs/engineering/*` as needed