docs: redefine phase 1 rebaseline steps

phases/1-linear-static-mitc4-rebaseline/step2.md

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+# Sprint Contract: Core Harness Guardrails
+
+## Objective
+Refresh the build, validation, core numeric aliases, DOF enum, and diagnostic guardrails so later MITC4 work has stable test foundations.
+
+## Required Reading
+- /AGENTS.md
+- /docs/ARCHITECTURE.md
+- /docs/ADR.md
+- /docs/NUMERICAL_CONVENTIONS.md
+- /docs/HARNESS_ENGINEERING.md
+- /scripts/validate_workspace.py
+
+## Scope
+- Preserve or repair CMake/CTest validation.
+- Verify `double` and signed int64 aliases are centralized.
+- Verify `UX`, `UY`, `UZ`, `RX`, `RY`, `RZ` mapping to Abaqus DOF `1..6`.
+- Improve diagnostics only where needed for later steps.
+
+## Allowed Files
+- `CMakeLists.txt`
+- `include/`
+- `src/`
+- `tests/`
+- `scripts/validate_workspace.py`
+- `PLAN.md`
+- `PROGRESS.md`
+
+## Explicit Non-Goals
+- Do not implement parser features.
+- Do not implement MITC4 stiffness.
+- Do not introduce MKL, TBB, or HDF5 APIs into solver core.
+
+## Tests To Write First
+- DOF enum and Abaqus DOF number mapping tests.
+- Numeric alias compile-time or runtime tests for `double` and int64 paths.
+- Validation script smoke test through `python scripts/validate_workspace.py`.
+
+## Reference Artifacts
+- None.
+
+## Acceptance Commands
+```bash
+python scripts/validate_workspace.py
+```
+
+## Evaluator Checklist
+- Core aliases and DOF mapping are not duplicated across modules.
+- Diagnostics include enough context for later parser, model, and singular errors.
+- Validation remains a real build plus test command.
+
+## Handoff Requirements
+- Record changed guardrails and test coverage in `PROGRESS.md`.
+- Leave future parser/MITC4 tasks in later step files.
+
+## Do Not
+- Do not weaken validation to make tests pass.
+- Do not add external library dependencies in this step.