docs: redefine phase 1 rebaseline steps

phases/1-linear-static-mitc4-rebaseline/step5.md

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+# Sprint Contract: Dof Manager Reaction Foundation
+
+## Objective
+Rebuild or verify the six-DOF `DofManager`, constrained/free mapping, equation numbering, sparse-pattern inputs, and full-vector reconstruction needed for reaction recovery.
+
+## Required Reading
+- /AGENTS.md
+- /docs/ARCHITECTURE.md
+- /docs/ADR.md
+- /docs/NUMERICAL_CONVENTIONS.md
+- /docs/RESULTS_SCHEMA.md
+
+## Scope
+- Manage active six-DOF shell nodes.
+- Apply fixed constraints by constrained DOF elimination.
+- Own equation numbering and sparse connectivity inputs.
+- Reconstruct full vectors in original global DOF order.
+- Provide data needed for `RF = K_full * U_full - F_full`.
+
+## Allowed Files
+- `include/`
+- `src/`
+- `tests/`
+- `PLAN.md`
+- `PROGRESS.md`
+
+## Explicit Non-Goals
+- Do not assemble MITC4 stiffness.
+- Do not store equation ids in `Node` or `Element`.
+- Do not compute `RF` from reduced vectors only.
+
+## Tests To Write First
+- DOF activation and Abaqus component order.
+- Constrained/free partition tests.
+- Equation numbering stability with noncontiguous node ids.
+- Full/reduced vector reconstruction tests.
+- Sparse-pattern connectivity input tests.
+- Full-vector reaction formula unit test with a small known matrix.
+
+## Reference Artifacts
+- None.
+
+## Acceptance Commands
+```bash
+python scripts/validate_workspace.py
+```
+
+## Evaluator Checklist
+- `DofManager` owns all equation numbering.
+- Full-space order is deterministic and matches `UX,UY,UZ,RX,RY,RZ`.
+- Reaction foundation preserves constrained DOF information.
+
+## Handoff Requirements
+- Record DOF and reaction foundation status in `PROGRESS.md`.
+
+## Do Not
+- Do not bypass `DofManager` from elements or analysis code.