docs: redefine phase 1 rebaseline steps

phases/1-linear-static-mitc4-rebaseline/step9.md

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+# Sprint Contract: MITC4 Material Integration
+
+## Objective
+Implement or rebuild local plane-stress material behavior, shear correction, material transformation, and `2 x 2 x 2` Gauss integration scaffolding.
+
+## Required Reading
+- /AGENTS.md
+- /docs/MITC4_FORMULATION.md
+- /docs/NUMERICAL_CONVENTIONS.md
+- /docs/ARCHITECTURE.md
+
+## Scope
+- Implement isotropic linear elastic shell material matrix with `sigma_33 = 0` and `kappa = 5/6`.
+- Define material/strain ordering tests.
+- Implement or verify convected-to-local material transformation for Phase 1 cases.
+- Add `2 x 2 x 2` integration point and weight infrastructure.
+
+## Allowed Files
+- `include/`
+- `src/`
+- `tests/`
+- `PLAN.md`
+- `PROGRESS.md`
+
+## Explicit Non-Goals
+- Do not add composite sections.
+- Do not add stress/strain output recovery as mandatory output.
+- Do not switch to analytic thickness integration without equivalence tests and doc update.
+
+## Tests To Write First
+- Isotropic matrix value tests for known `E`, `nu`, and `kappa`.
+- Shear row ordering tests.
+- Integration point count and weights tests.
+- Flat element material transform identity/equivalence tests.
+- Invalid material/thickness diagnostic tests if not covered earlier.
+
+## Reference Artifacts
+- None.
+
+## Acceptance Commands
+```bash
+python scripts/validate_workspace.py
+```
+
+## Evaluator Checklist
+- `2 x 2 x 2` integration is the active baseline.
+- Material transform behavior is tested.
+- No reduced integration or hourglass logic is introduced.
+
+## Handoff Requirements
+- Record material and integration readiness in `PROGRESS.md`.
+
+## Do Not
+- Do not make S4R assumptions in material or integration code.