docs: redefine phase 1 rebaseline steps

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

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+# Sprint Contract: Rebaseline Audit
+
+## Objective
+Audit the existing Phase 1 implementation against the paper-based `docs/MITC4_FORMULATION.md` and produce a concrete rework map before changing solver behavior.
+
+## 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
+- /docs/MITC4_FORMULATION.md
+- /phases/1-linear-static-mitc4/index.json
+
+## Scope
+- Inspect existing C++ implementation and tests only enough to classify what can be retained, rewritten, or deleted in later steps.
+- Produce or update planning notes in `PLAN.md` and `PROGRESS.md`.
+- If useful, add a short audit artifact under `phases/1-linear-static-mitc4-rebaseline/`.
+
+## Allowed Files
+- `PLAN.md`
+- `PROGRESS.md`
+- `phases/1-linear-static-mitc4-rebaseline/`
+
+## Explicit Non-Goals
+- Do not change production C++ behavior.
+- Do not rewrite MITC4 formulas.
+- Do not unblock stored-reference regression by accepting unsupported Abaqus syntax.
+
+## Tests To Write First
+- None. This is a planning and audit sprint.
+
+## Reference Artifacts
+- `references/quad_01.inp`
+- `references/quad_01_displacements.csv`
+- `references/quad_02.inp`
+- `references/quad_02_displacements.csv`
+
+## Acceptance Commands
+```bash
+python scripts/validate_workspace.py
+```
+
+## Evaluator Checklist
+- The audit identifies conflicts with `docs/MITC4_FORMULATION.md`, especially old averaged-edge basis, `1.0e-6` drilling scale, analytic thickness integration, and direct shear evaluation risks.
+- Future work is assigned to later rebaseline steps instead of being fixed here.
+- `PLAN.md` and `PROGRESS.md` describe the new state without treating the old P1-01 through P1-14 implementation as authoritative.
+
+## Handoff Requirements
+- Record completed audit work in `PROGRESS.md`.
+- Keep next implementation tasks in `PLAN.md` or later step files.
+
+## Do Not
+- Do not merge this audit with implementation.
+- Do not remove old phase history.