rtx-fea: re-enable the remaining CPU test modules; fix three real defects they caught

All 33 remaining #[cfg(disabled)] test modules outside the GPU cluster are
now enabled: assembly (dof_mapping, constraints, global assembly), boundary
(mod + dirichlet/neumann/robin/thermal/contact), analysis (mod + static),
materials (mod, linear_elastic, hyperelastic, plasticity), elements (mod,
element_matrices, isoparametric, jacobian, quadrature), mesh (element_types,
connectivity, topology, topology_repair), solvers (mod, direct, iterative,
nonlinear) and lib.rs. Lib tests 117 -> 335, stable across repeated runs.
Only gpu_solver_tests and the GpuMeshData fixture stay disabled — they need
CUDA hardware and belong to the GPU tranche.

Three real defects found by the newly-compiling tests, each fixed:

- Direct solvers reused factorizations keyed on matrix SIZE alone.
  In a Newton loop the Jacobian changes every iteration but never its
  dimension, so LuDirect/CholeskyDirect/LdltDirect silently solved with the
  first iteration's factorization forever — Newton on x^2-4 crawled to
  x=1.955 in 1000 iterations instead of converging in 5. Invisible in
  single-solve linear analysis, which is why every green test passed over
  it. solve() now factorizes the matrix it is given.

- AdaptiveQuadrature's refinement re-integrated the WHOLE domain once per
  subdomain, so each level multiplied the estimate by the subdomain count:
  integrating e^x over [-1,1] at tolerance 1e-10 returned ~75 instead of
  2.35. The recursion now descends into each sub-box with its share of the
  error budget.

- compute_skewness read Jacobian columns as coordinate-line tangents, but
  the trait's jacobian() stores tangents in ROWS: on a sheared
  parallelogram whose tangents meet at 14 degrees it reported skewness 0.43
  instead of 0.84 — measuring per-component gradients, not mesh skew.

Fixtures corrected rather than the code where the fixture was wrong:
sigma_yy ~ 0 asserted uniaxial-stress physics on a uniaxial-strain state
(exact Lame values now asserted); an "unstable" orthotropic parameter set
that satisfies the determinant stability condition (delta = 0.187 > 0); a
unit-cube hex Jacobian of 1.0 that assumed a unit reference element (it is
0.125 from [-1,1]^3); a "distorted" quad whose centre Jacobian is exactly
orthogonal, asserted as skewed (flattening and shearing now tested
separately); a quality score below the implementation's own calibration;
Rayleigh damping fed the scalar-field mass (now expanded via the Kronecker
identity, with C = alpha*M + beta*K asserted entry-wise); an element
factory required to construct Point/Line types that have no implementation;
and DOF counts that encoded the repaired 3-DOFs-per-node-on-2-D defect.

MaterialDatabase::add_material call sites updated to the (id, material,
name) signature; ConnectivityInfo::build takes elements only;
TopologyRepair::triangle_quality (normalized 4*sqrt(3)*A/sum(a^2)) added
for the repair tests; create_subdomain_rule_* widened to pub(super) for the
quadrature tests.

Co-Authored-By: Claude Fable 5 <[email protected]>

crates/specialized/rtx-fea/src/materials/hyperelastic.rs

@@ -330,7 +330,7 @@ impl Material for MooneyRivlin {
     }
 }
 
-#[cfg(disabled)]
+#[cfg(test)]
 mod tests {
     use super::*;
 

crates/specialized/rtx-fea/src/materials/linear_elastic.rs

@@ -474,7 +474,7 @@ impl Material for TransverselyIsotropic {
     }
 }
 
-#[cfg(disabled)]
+#[cfg(test)]
 mod tests {
     use super::*;
 
@@ -486,17 +486,30 @@ mod tests {
         assert!(material.is_linear());
     }
 
+    // Fixture correction on re-enable (2026-08-19): the original expected
+    // sigma_yy ~ 0 "due to the Poisson effect". That is uniaxial-STRESS
+    // physics; the applied state here is uniaxial STRAIN (eps_yy = eps_zz =
+    // 0), where full 3-D Hooke's law gives sigma_yy = lambda*eps_xx != 0.
+    // Assert the exact Lame values instead.
     #[test]
     fn test_linear_elastic_response() {
-        let material = LinearElastic::new(200e9, 0.3);
-        let strain = Vector6::new(0.001, 0.0, 0.0, 0.0, 0.0, 0.0);
+        let (e, nu, eps) = (200e9, 0.3, 0.001);
+        let material = LinearElastic::new(e, nu);
+        let strain = Vector6::new(eps, 0.0, 0.0, 0.0, 0.0, 0.0);
         let state = MaterialState::default();
 
         let response = material.compute_response(&strain, &state, 1.0).unwrap();
 
+        let lambda = e * nu / ((1.0 + nu) * (1.0 - 2.0 * nu));
+        let mu = e / (2.0 * (1.0 + nu));
+
         assert!(response.is_valid);
-        assert!(response.stress[0] > 0.0); // Should have positive stress in x-direction
-        assert!((response.stress[1]).abs() < 1e-6); // Should have minimal stress in y-direction due to Poisson effect
+        assert!((response.stress[0] - (lambda + 2.0 * mu) * eps).abs() < 1.0);
+        assert!((response.stress[1] - lambda * eps).abs() < 1.0);
+        assert!((response.stress[2] - lambda * eps).abs() < 1.0);
+        for i in 3..6 {
+            assert!((response.stress[i]).abs() < 1e-9);
+        }
     }
 
     #[test]
@@ -567,12 +580,18 @@ mod tests {
         let result = OrthotropicElastic::new(-200e9, 15e9, 15e9, 0.25, 0.25, 0.5, 5e9, 5e9, 5e9);
         assert!(result.is_err());
 
-        // Invalid case: violates stability condition
-        let result = OrthotropicElastic::new(
-            200e9, 15e9, 15e9, 0.8, 0.8, 0.8, // High Poisson's ratios
-            5e9, 5e9, 5e9,
-        );
+        // Invalid case: violates the determinant stability condition. The
+        // original fixture used (E1=200, E2=E3=15) GPa with nu = 0.8, which is
+        // actually STABLE — nu21 = nu12*E2/E1 shrinks the reciprocal products
+        // to delta = 0.187 > 0. Equal moduli with nu = 0.6 genuinely violate
+        // it: delta = 1 - 3*0.36 - 2*0.216 < 0.
+        let result = OrthotropicElastic::new(200e9, 200e9, 200e9, 0.6, 0.6, 0.6, 5e9, 5e9, 5e9);
         assert!(result.is_err());
+
+        // And the original "high Poisson" case must construct, since it
+        // satisfies the stability condition.
+        let result = OrthotropicElastic::new(200e9, 15e9, 15e9, 0.8, 0.8, 0.8, 5e9, 5e9, 5e9);
+        assert!(result.is_ok());
     }
 
     #[test]

crates/specialized/rtx-fea/src/materials/mod.rs

@@ -715,7 +715,7 @@ pub mod utils {
     }
 }
 
-#[cfg(disabled)]
+#[cfg(test)]
 mod tests {
     use super::*;
 

crates/specialized/rtx-fea/src/materials/plasticity.rs

@@ -160,7 +160,7 @@ impl Material for IsotropicPlasticity {
     }
 }
 
-#[cfg(disabled)]
+#[cfg(test)]
 mod tests {
     use super::*;