docs: redefine phase 1 rebaseline steps

phases/1-linear-static-mitc4-rebaseline/step3.md

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+# Sprint Contract: Parser Domain Subset
+
+## Objective
+Revalidate and repair the Phase 1 Abaqus parser and `Domain` model against the documented subset while preserving strict rejection of unsupported reference features.
+
+## Required Reading
+- /AGENTS.md
+- /docs/ARCHITECTURE.md
+- /docs/ADR.md
+- /docs/ABAQUS_INPUT_SUBSET.md
+- /docs/VERIFICATION_PLAN.md
+- /docs/MITC4_FORMULATION.md
+
+## Scope
+- Parse Phase 1 keywords into immutable `Domain` objects.
+- Preserve node, element, set, material, shell section, boundary, load, and step definitions.
+- Reject `S4R`, `Part/Assembly/Instance`, `*Include`, `NLGEOM=YES`, nonzero prescribed displacement, and unsupported material/section modes.
+
+## Allowed Files
+- `include/`
+- `src/`
+- `tests/`
+- `docs/ABAQUS_INPUT_SUBSET.md` only for clarifying parser contract
+- `PLAN.md`
+- `PROGRESS.md`
+
+## Explicit Non-Goals
+- Do not implement analysis or assembly.
+- Do not add `Part/Assembly/Instance` support because `quad_02` contains it.
+- Do not normalize reference files in parser code.
+
+## Tests To Write First
+- Parser acceptance tests for every Phase 1 keyword.
+- Generated and explicit `*Nset` and `*Elset` tests.
+- Unsupported feature rejection tests for `S4R`, `Part`, `Assembly`, `Instance`, `*Density`, and `NLGEOM=YES`.
+- Line-numbered diagnostic tests for malformed numeric and DOF fields.
+
+## Reference Artifacts
+- `references/quad_01.inp` as unsupported provenance.
+- `references/quad_02.inp` as unsupported original provenance until normalized or parser scope changes.
+
+## Acceptance Commands
+```bash
+python scripts/validate_workspace.py
+```
+
+## Evaluator Checklist
+- Parser behavior matches `docs/ABAQUS_INPUT_SUBSET.md`.
+- `TYPE=S4` maps to internal MITC4.
+- Unsupported stored references are not silently accepted.
+- Domain objects do not own equation numbers.
+
+## Handoff Requirements
+- Update `PROGRESS.md` with parser status.
+- Update `PLAN.md` for unresolved reference compatibility work.
+
+## Do Not
+- Do not broaden the parser subset without ADR and doc updates.