feat: add mitc4 material integration scaffolding

PROGRESS.md

@@ -13,10 +13,36 @@ Every new agent session must read this file together with `PLAN.md` before plann
 - Do not remove history unless the user explicitly asks for archival cleanup.
 
 ## Current Status
-Phase 1 has a new rebaseline phase definition in `phases/1-linear-static-mitc4-rebaseline`. Steps 0 through 8 are complete. `quad_02_phase1.inp` is now the normalized Phase 1-compatible input path for the stored `quad_02` S4 reference pair, while the original `quad_02.inp` remains preserved unsupported provenance. Core numeric aliases, DOF mapping, validation harness, model diagnostic context, the Phase 1 parser/domain subset, validation/singular diagnostics, DofManager/reaction foundation, minimum result model metadata, displacement CSV comparator foundation, MITC4 geometry/director scaffolding, and MITC4 displacement/strain/tying row scaffolding have been revalidated. The old `phases/1-linear-static-mitc4` path is historical and superseded after the MITC4 formulation reset.
+Phase 1 has a new rebaseline phase definition in `phases/1-linear-static-mitc4-rebaseline`. Steps 0 through 9 are complete. `quad_02_phase1.inp` is now the normalized Phase 1-compatible input path for the stored `quad_02` S4 reference pair, while the original `quad_02.inp` remains preserved unsupported provenance. Core numeric aliases, DOF mapping, validation harness, model diagnostic context, the Phase 1 parser/domain subset, validation/singular diagnostics, DofManager/reaction foundation, minimum result model metadata, displacement CSV comparator foundation, MITC4 geometry/director scaffolding, MITC4 displacement/strain/tying row scaffolding, and MITC4 material/transform/integration scaffolding have been revalidated. The old `phases/1-linear-static-mitc4` path is historical and superseded after the MITC4 formulation reset.
 
 ## Completed Work
 
+### 2026-05-04 - P1R-09 MITC4 material integration scaffolding completed
+Author: Codex
+
+Changed files:
+- `include/fesa/fesa.hpp`
+- `tests/test_main.cpp`
+- `phases/1-linear-static-mitc4-rebaseline/index.json`
+- `PLAN.md`
+- `PROGRESS.md`
+
+Summary:
+- Added tests and implementation for the documented isotropic local plane-stress shell material matrix in strain order `[eps11, eps22, eps33, gamma23, gamma13, gamma12]`, with `sigma_33 = 0` and transverse shear correction `kappa = 5/6`.
+- Added material diagnostics for invalid elastic modulus, Poisson ratio, and shear correction factor.
+- Added `2 x 2 x 2` Gauss integration point infrastructure with unit weights and total natural-domain weight `8`.
+- Added covariant-to-local strain transformation and `D_convected = T^T D_hat T`, including identity and flat-element energy-equivalence tests.
+- Added MITC4 material integration sample scaffolding that carries integration basis, tied strain rows, local material, strain transform, and convected material for the later stiffness rebuild.
+
+Verification:
+- First ran `python scripts/validate_workspace.py` after adding Step 9 tests; it failed as expected because the MITC4 material/integration APIs did not exist yet.
+- After implementation, `python scripts/validate_workspace.py` configured CMake, built `fesa_core` and `fesa_tests`, and ran CTest successfully.
+- CTest result: 1 test executable passed.
+
+Follow-up:
+- Continue with P1R-10 MITC4 stiffness/internal force rebuild, six-DOF local-to-global transform, and drilling stabilization.
+- The legacy `MITC4ElementKernel::stiffness` path still needs to be rebuilt against the Step 7 through Step 9 formulation helpers; Step 9 intentionally did not add reduced integration, hourglass logic, stress/result output recovery, or the final drilling stiffness policy.
+
 ### 2026-05-04 - P1R-08 MITC4 covariant strain tying completed
 Author: Codex