test: Java golden-value oracles for the five DCE math cores + P1-2/P1-3 fixes

Add bit-for-bit (1e-12) golden-value oracle tests pinning the C++ pure-math
and functional cores against the compiled upstream Java library (openjdk 17):

- HyperIdealGoldenJava: Clausen/Л/ImLi2, ζ13/14/15/ζ, both tetrahedron-volume
  formulas (real de.varylab…Clausen / HyperIdealUtility).
- EuclideanGoldenJava / SphericalGoldenJava: angle formulas + β relations + Л
  energy terms, plus FULL-MESH oracles driving the real EuclideanCyclicFunctional
  / SphericalFunctional on a shared tetrahedron — per-vertex gradient (Θ−Σα) and
  ΔE = E(x)−E(0) (C++ Gauss-Legendre path integral vs Java closed form).
- SphericalGoldenJava.FullMeshEdgeDofGradient: edge-DOF gradient (vertex + edge
  components, α_opp⁺+α_opp⁻−θ_e) vs raw conformalEnergyAndGradient — locks
  Finding 3 at the solution level (audit items 4 & 5).
- PeriodMatrix.NormalizeModulus_GoldenJava: τ-reduction fold convention vs the
  real DiscreteEllipticUtility.normalizeModulus (audit items 7 & 8).

Subtlety documented: the spherical oracles call Java's raw
conformalEnergyAndGradient, not evaluate() (which pre-runs a Brent gauge
maximization that C++ factors into the Newton solver's spherical_gauge_shift).

Also:
- P1-2 (layout.hpp): Euclidean holonomy now uses a per-cut-edge rigid-motion fit
  g(z)=a·z+b, exposing residual_rotation = |arg(a)| as a diagnostic; non-
  regressive (flat case a=1 reduces to the old midpoint formula).
- P1-3 (period_matrix.hpp): is_in_fundamental_domain fixed to the correct
  half-open SL(2,ℤ) domain (−½ ≤ Re < ½). Updated the now-exposed
  ComputePeriodMatrix_ReducedTau_InFD to assert the normalizeModulus domain
  (closed +½ edge) instead.

Test counts (single source of truth = doc/api/tests.md): 272/272 pass, 0
skipped (26 non-CGAL + 246 CGAL).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

code/tests/cgal/test_euclidean_functional.cpp

@@ -26,6 +26,7 @@
 #include "euclidean_geometry.hpp"
 #include "euclidean_functional.hpp"
 #include "euclidean_hessian.hpp"
+#include "clausen.hpp"
 #include <gtest/gtest.h>
 #include <cmath>
 #include <vector>
@@ -290,3 +291,117 @@ TEST(EuclideanFunctional, GradientCheck_MixedPinnedVertices)
     EXPECT_TRUE(gradient_check_euclidean(mesh, x, maps))
         << "Gradient check failed for mixed pinned/variable vertices";
 }
+
+// ─────────────────────────────────────────────────────────────────────────────
+// Golden-value oracle — pin the Euclidean angle formula and the 2·Л(α) energy
+// term bit-for-bit against the upstream Java reference (EuclideanCyclicFunctional
+// .triangleEnergyAndAlphas, lines 341-361), captured by running the compiled Java
+// library (openjdk 17) with the real de.varylab…Clausen.Л on these exact edge
+// lengths.  Companion to HyperIdealGoldenJava and SphericalGoldenJava: locks the
+// absolute angle/energy values against an independent implementation, catching
+// silent index/sign drift the curl-free path-integral gradient check cannot see.
+//
+// To regenerate: /tmp/oracle/EucOracle.java.  Values are Java printf %.17g.
+// ─────────────────────────────────────────────────────────────────────────────
+TEST(EuclideanGoldenJava, AngleAndLobachevskyEnergyFromLengths)
+{
+    auto check = [](double l12, double l23, double l31,
+                    double a1_g, double a2_g, double a3_g, double L_g) {
+        auto fa = euclidean_angles_from_lengths(l12, l23, l31);
+        EXPECT_TRUE(fa.valid);
+        EXPECT_NEAR(fa.alpha1, a1_g, 1e-12);
+        EXPECT_NEAR(fa.alpha2, a2_g, 1e-12);
+        EXPECT_NEAR(fa.alpha3, a3_g, 1e-12);
+        const double Lterm = 2.0 * Lobachevsky(fa.alpha1)
+                           + 2.0 * Lobachevsky(fa.alpha2)
+                           + 2.0 * Lobachevsky(fa.alpha3);
+        EXPECT_NEAR(Lterm, L_g, 1e-12);
+    };
+    check(1.0, 1.2, 0.9,
+          1.3637649752769678, 0.82416964552030680, 0.95365803279251860,
+          1.9456273836230942);
+    check(1.0, 1.0, 1.0,
+          1.0471975511965979, 1.0471975511965979, 1.0471975511965979,
+          2.0298832128193070);
+}
+
+// ─────────────────────────────────────────────────────────────────────────────
+// FULL-MESH golden oracle — the strongest cross-check: drives the REAL upstream
+// EuclideanCyclicFunctional (openjdk 17) on a tetrahedron loaded from a shared
+// OBJ (identical topology + geometry to make_tetrahedron()), and pins BOTH the
+// per-vertex gradient G_v = Θ_v − Σα AND the energy difference ΔE = E(x) − E(0)
+// bit-for-bit against it.
+//
+// This closes audit missing-test item 5 (full-mesh energy + gradient at a known
+// x).  It is genuinely independent of the C++ implementation in two ways:
+//   • the gradient is the upstream library's own analytic gradient (not an FD
+//     check, which only proves curl-freeness of the C++ self-consistent energy);
+//   • the energy is Java's CLOSED-FORM functional value, whereas C++ computes it
+//     as a Gauss-Legendre PATH INTEGRAL of its gradient — two different methods
+//     that must agree on ΔE (the initialEnergy constant and the φ·λ⁰ term cancel
+//     in the difference, and there are no edge DOFs here).
+//
+// Setup parity (verified against UnwrapUtility.prepareInvariantDataEuclidean):
+//   closed mesh, ALL 4 vertices variable (no pin), Θ_v = 2π, no edge DOFs,
+//   λ°_e = 2·log(|p_i − p_j|), per-vertex u(P) = 0.10·X − 0.07·Y + 0.13·Z.
+//
+// To regenerate: /tmp/oracle/{tet.obj,EucMeshOracle.java}.  Values are Java %.17g.
+// ─────────────────────────────────────────────────────────────────────────────
+TEST(EuclideanGoldenJava, FullMeshGradientAndEnergy_Tetrahedron)
+{
+    constexpr double TWO_PI = 2.0 * 3.14159265358979323846264338328;
+
+    auto mesh = make_tetrahedron();   // same 4 vertices as /tmp/oracle/tet.obj
+    auto maps = setup_euclidean_maps(mesh);
+    compute_euclidean_lambda0_from_mesh(mesh, maps);
+
+    // All four vertices are DOFs (Java prepareInvariantData makes every interior
+    // vertex variable on a closed mesh); Θ_v = 2π; no edge DOFs.
+    int idx = 0;
+    for (auto v : mesh.vertices()) {
+        maps.v_idx[v]   = idx++;
+        maps.theta_v[v] = TWO_PI;
+    }
+
+    auto u_of = [](const Point3& p) {
+        return 0.10 * p.x() - 0.07 * p.y() + 0.13 * p.z();
+    };
+
+    std::vector<double> x(static_cast<std::size_t>(idx), 0.0);
+    for (auto v : mesh.vertices())
+        x[static_cast<std::size_t>(maps.v_idx[v])] = u_of(mesh.point(v));
+
+    auto G = euclidean_gradient(mesh, x, maps);
+
+    // Java golden gradients keyed by vertex position (order-independent lookup).
+    struct GoldRow { double X, Y, Z, G; };
+    const GoldRow gold[4] = {
+        { 1,  1,  1, 3.5277511803984396},
+        { 1, -1, -1, 3.2837611905358440},
+        {-1,  1, -1, 2.3437485291237100},
+        {-1, -1,  1, 3.4111097143011780},
+    };
+    for (auto v : mesh.vertices()) {
+        const auto& p = mesh.point(v);
+        const double g = G[static_cast<std::size_t>(maps.v_idx[v])];
+        bool matched = false;
+        for (const auto& row : gold) {
+            if (std::abs(p.x() - row.X) < 1e-9 &&
+                std::abs(p.y() - row.Y) < 1e-9 &&
+                std::abs(p.z() - row.Z) < 1e-9) {
+                EXPECT_NEAR(g, row.G, 1e-12)
+                    << "gradient mismatch at (" << p.x() << "," << p.y()
+                    << "," << p.z() << ")";
+                matched = true;
+                break;
+            }
+        }
+        EXPECT_TRUE(matched) << "unexpected vertex position";
+    }
+
+    // ΔE = E(x) − E(0).  C++ path integral vs Java closed-form functional value.
+    std::vector<double> x0(static_cast<std::size_t>(idx), 0.0);
+    const double dE = euclidean_energy(mesh, x, maps)
+                    - euclidean_energy(mesh, x0, maps);
+    EXPECT_NEAR(dE, 0.15962619236187336, 1e-12);
+}

code/tests/cgal/test_phase7.cpp

@@ -338,12 +338,52 @@ TEST(PeriodMatrix, ComputePeriodMatrix_UnitSquare)
 TEST(PeriodMatrix, ComputePeriodMatrix_ReducedTau_InFD)
 {
     // ω_1 = (1, 0), ω_2 = (0.5, 0.25)  →  τ = 0.5 + 0.25i
-    // |τ| = sqrt(0.25 + 0.0625) ≈ 0.559 < 1 → needs S step
+    // |τ| = sqrt(0.25 + 0.0625) ≈ 0.559 < 1 → needs S step.
+    // compute_period_matrix reduces with normalizeModulus (Finding 6), whose
+    // mirror-folded target domain is { 0 ≤ Re ≤ ½, Im > 0, |τ| ≥ 1 } — note the
+    // RIGHT boundary Re = +½ is CLOSED here.  This is NOT the half-open SL(2,ℤ)
+    // domain of is_in_fundamental_domain (−½ ≤ Re < ½), which excludes Re = +½
+    // because +½ ≡ −½ under T.  For this input normalizeModulus lands exactly on
+    // τ = ½ + i, so we must check the normalizeModulus domain, not the SL(2,ℤ)
+    // one (asserting is_in_fundamental_domain here would wrongly fail on +½).
     HolonomyData hol;
     hol.translations = { Eigen::Vector2d(1.0, 0.0), Eigen::Vector2d(0.5, 0.25) };
     PeriodData pd = compute_period_matrix(hol, /*reduce=*/true);
     EXPECT_TRUE(pd.in_fundamental_domain);
-    EXPECT_TRUE(is_in_fundamental_domain(pd.tau, 1e-9));
+    const double tol = 1e-9;
+    EXPECT_GT(pd.tau.imag(), 0.0);
+    EXPECT_GE(pd.tau.real(), 0.0 - tol);          // 0 ≤ Re   (mirror fold)
+    EXPECT_LE(pd.tau.real(), 0.5 + tol);          // Re ≤ ½   (closed right edge)
+    EXPECT_GE(std::abs(pd.tau), 1.0 - tol);       // |τ| ≥ 1
+    // Concretely: τ = ½ + i.
+    EXPECT_NEAR(pd.tau.real(), 0.5, 1e-12);
+    EXPECT_NEAR(pd.tau.imag(), 1.0, 1e-12);
+}
+
+// ─────────────────────────────────────────────────────────────────────────────
+// Golden-value oracle — pin normalizeModulus (the τ reduction used by
+// compute_period_matrix, Finding 6) bit-for-bit against the upstream Java
+// reference (de.varylab.discreteconformal.util.DiscreteEllipticUtility.
+// normalizeModulus), captured by calling the compiled Java method (openjdk 17)
+// on these exact τ.  This locks the sign/fold conventions of the SL(2,ℤ)+mirror
+// reduction (0 ≤ Re ≤ ½, Im ≥ 0, |τ| ≥ 1) against an independent implementation,
+// catching drift the existing in-FD membership checks cannot (they only assert
+// the result lies in F, not that it is the SAME representative Java picks).
+//
+// To regenerate: /tmp/oracle/TauOracle.java.  Values are Java printf %.17g.
+// ─────────────────────────────────────────────────────────────────────────────
+TEST(PeriodMatrix, NormalizeModulus_GoldenJava)
+{
+    auto chk = [](double re, double im, double re_g, double im_g) {
+        C n = conformallab::normalizeModulus(C(re, im));
+        EXPECT_NEAR(n.real(), re_g, 1e-12);
+        EXPECT_NEAR(n.imag(), im_g, 1e-12);
+    };
+    chk(0.3, 0.5,  0.11764705882352933, 1.4705882352941178);  // |τ|<1 → S + folds
+    chk(-0.4, 1.3, 0.40000000000000000, 1.3000000000000000);  // Re<0 mirror fold
+    chk(2.7, 0.8,  0.41095890410958880, 1.0958904109589043);  // large Re → T
+    chk(0.1, 2.0,  0.10000000000000000, 2.0000000000000000);  // already in F
+    chk(-1.6, 0.9, 0.41237113402061850, 0.92783505154639180); // T + S + mirror
 }
 
 // ════════════════════════════════════════════════════════════════════════════

code/tests/cgal/test_spherical_functional.cpp

@@ -27,6 +27,8 @@
 #include "mesh_builder.hpp"
 #include "spherical_functional.hpp"
 #include "spherical_hessian.hpp"
+#include "spherical_geometry.hpp"
+#include "clausen.hpp"
 #include <gtest/gtest.h>
 #include <cmath>
 #include <vector>
@@ -416,3 +418,237 @@ TEST(SphericalFunctional, GaugeFix_AlreadyAtGaugeReturnsTNearZero)
     EXPECT_NEAR(t, 0.0, 1e-5)
         << "Gauge shift from the symmetric point should be ~0; got " << t;
 }
+
+// ─────────────────────────────────────────────────────────────────────────────
+// Golden-value oracle — pin the spherical law-of-cosines angle formula, the β
+// half-angle relations, and the Lobachevsky energy term bit-for-bit against the
+// upstream Java reference (SphericalFunctional.triangleEnergyAndAlphas, lines
+// 401-453), captured by running the compiled Java library (openjdk 17) with the
+// real de.varylab…Clausen.Л on these exact arc lengths.  Unlike the Schläfli
+// path-integral gradient check (which only verifies curl-freeness), this locks
+// the absolute angle/β/energy values against an independent implementation,
+// catching any silent index/sign/convention drift in the spherical port.
+//
+// To regenerate: /tmp/oracle/SphereOracle.java (recipe in doc/reviewer/
+// java-port-audit.md).  Values are Java printf %.17g.  Tolerance 1e-12.
+//
+// Index map (C++ spherical_angles ↔ Java): with l12=lij, l23=ljk, l31=lki the
+// returned alpha1/alpha2/alpha3 are Java αi/αj/αk (angle opposite ljk/lki/lij).
+// ─────────────────────────────────────────────────────────────────────────────
+TEST(SphericalGoldenJava, AngleBetaEnergyFromLengths)
+{
+    auto check = [](double lij, double ljk, double lki,
+                    double ai_g, double aj_g, double ak_g,
+                    double bi_g, double bj_g, double bk_g, double L_g) {
+        auto fa = spherical_angles(lij, ljk, lki);
+        EXPECT_TRUE(fa.valid);
+        EXPECT_NEAR(fa.alpha1, ai_g, 1e-12);
+        EXPECT_NEAR(fa.alpha2, aj_g, 1e-12);
+        EXPECT_NEAR(fa.alpha3, ak_g, 1e-12);
+
+        const double ai = fa.alpha1, aj = fa.alpha2, ak = fa.alpha3;
+        const double bi = 0.5 * (PI + ai - aj - ak);
+        const double bj = 0.5 * (PI - ai + aj - ak);
+        const double bk = 0.5 * (PI - ai - aj + ak);
+        EXPECT_NEAR(bi, bi_g, 1e-12);
+        EXPECT_NEAR(bj, bj_g, 1e-12);
+        EXPECT_NEAR(bk, bk_g, 1e-12);
+
+        const double Lterm =
+            Lobachevsky(ai) + Lobachevsky(aj) + Lobachevsky(ak) +
+            Lobachevsky(bi) + Lobachevsky(bj) + Lobachevsky(bk) +
+            Lobachevsky(0.5 * (PI - ai - aj - ak));
+        EXPECT_NEAR(Lterm, L_g, 1e-12);
+    };
+
+    // Scalene spherical triangle (all Δ > 0, Δ_ijk < 2π).
+    check(1.0, 1.2, 0.9,
+          1.5305813141072122, 0.99684981272794600, 1.1246069519101605,
+          1.2753586015294494, 0.74162710015018330, 0.86938423933239760,
+          1.3576100185550408);
+    // Equilateral spherical triangle.
+    check(0.7, 0.7, 0.7,
+          1.1225596283199812, 1.1225596283199812, 1.1225596283199812,
+          1.0095165126349062, 1.0095165126349060, 1.0095165126349060,
+          1.6806828584976297);
+}
+
+// ─────────────────────────────────────────────────────────────────────────────
+// FULL-MESH golden oracle (spherical) — drives the REAL upstream SphericalFunctional
+// on the shared tetrahedron (scaled so every arc length stays < π) and pins BOTH
+// the per-vertex gradient G_v = Θ_v − Σα AND ΔE = E(x) − E(0) bit-for-bit.
+//
+// IMPORTANT — the oracle calls Java's `conformalEnergyAndGradient` (the RAW
+// θ−Σα gradient), NOT `evaluate()`: `evaluate()` first runs a 1-D Brent
+// maximization over the global-scale gauge direction (`maximizeInNegativeDirection`),
+// which the C++ `spherical_gradient` deliberately does NOT — C++ factors that
+// gauge into the Newton solver's `spherical_gauge_shift` instead.  Comparing
+// against `evaluate()` would (wrongly) drive every component to ~0.  The raw
+// gradient is the piece that corresponds 1:1 to the C++ functional.
+//
+// Setup parity (UnwrapUtility.prepareInvariantDataHyperbolicAndSpherical, scale):
+//   closed mesh, ALL 4 vertices variable, Θ_v = 2π, no edge DOFs,
+//   λ°_e = 2·log(SCALE·|p_i − p_j|)  (Java uses chord length × scale, whereas the
+//   C++ compute_lambda0_from_mesh helper assumes unit-sphere vertices and uses
+//   ARC length — so we set λ° directly here to match Java exactly),
+//   per-vertex u(P) = 0.10·X − 0.07·Y + 0.13·Z, SCALE = 0.2.
+//
+// To regenerate: /tmp/oracle/{tet.obj,SphereMeshOracle.java}.  Values are Java %.17g.
+// ─────────────────────────────────────────────────────────────────────────────
+TEST(SphericalGoldenJava, FullMeshGradientAndEnergy_Tetrahedron)
+{
+    constexpr double TWO_PI = 2.0 * 3.14159265358979323846264338328;
+    constexpr double SCALE  = 0.2;
+
+    auto mesh = make_tetrahedron();   // same 4 vertices as /tmp/oracle/tet.obj
+    auto maps = setup_spherical_maps(mesh);
+
+    // λ°_e = 2·log(SCALE · chord), matching Java's prepareInvariantData(scale).
+    for (auto e : mesh.edges()) {
+        auto h  = mesh.halfedge(e);
+        const auto& p1 = mesh.point(mesh.source(h));
+        const auto& p2 = mesh.point(mesh.target(h));
+        const double dx = p1.x() - p2.x(), dy = p1.y() - p2.y(), dz = p1.z() - p2.z();
+        const double chord = std::sqrt(dx*dx + dy*dy + dz*dz);
+        maps.lambda0[e] = 2.0 * std::log(SCALE * chord);
+    }
+
+    int idx = 0;
+    for (auto v : mesh.vertices()) {
+        maps.v_idx[v]   = idx++;
+        maps.theta_v[v] = TWO_PI;
+    }
+
+    auto u_of = [](const Point3& p) {
+        return 0.10 * p.x() - 0.07 * p.y() + 0.13 * p.z();
+    };
+
+    std::vector<double> x(static_cast<std::size_t>(idx), 0.0);
+    for (auto v : mesh.vertices())
+        x[static_cast<std::size_t>(maps.v_idx[v])] = u_of(mesh.point(v));
+
+    auto G = spherical_gradient(mesh, x, maps);
+
+    struct GoldRow { double X, Y, Z, G; };
+    const GoldRow gold[4] = {
+        { 1,  1,  1, 2.7671034786104927},
+        { 1, -1, -1, 2.5216834054857546},
+        {-1,  1, -1, 1.5401761310866633},
+        {-1, -1,  1, 2.6518569531861100},
+    };
+    for (auto v : mesh.vertices()) {
+        const auto& p = mesh.point(v);
+        const double g = G[static_cast<std::size_t>(maps.v_idx[v])];
+        bool matched = false;
+        for (const auto& row : gold) {
+            if (std::abs(p.x() - row.X) < 1e-9 &&
+                std::abs(p.y() - row.Y) < 1e-9 &&
+                std::abs(p.z() - row.Z) < 1e-9) {
+                EXPECT_NEAR(g, row.G, 1e-12)
+                    << "gradient mismatch at (" << p.x() << "," << p.y()
+                    << "," << p.z() << ")";
+                matched = true;
+                break;
+            }
+        }
+        EXPECT_TRUE(matched) << "unexpected vertex position";
+    }
+
+    std::vector<double> x0(static_cast<std::size_t>(idx), 0.0);
+    const double dE = spherical_energy(mesh, x, maps)
+                    - spherical_energy(mesh, x0, maps);
+    EXPECT_NEAR(dE, 0.16409141487397116, 1e-12);
+}
+
+// ─────────────────────────────────────────────────────────────────────────────
+// FULL-MESH EDGE-DOF golden oracle (spherical, Finding 3) — the missing solution-
+// level Java oracle for the edge-DOF gradient path.  Makes two opposite edges of
+// the shared tetrahedron variable (replacement parameterization: λ_e = x[e_idx],
+// no u-shift) and pins BOTH the vertex gradient (Θ−Σα) AND the edge gradient
+// (α_opp⁺ + α_opp⁻ − θ_e, θ_e = π) bit-for-bit against the REAL upstream
+// SphericalFunctional.conformalEnergyAndGradient (raw gradient, not evaluate()).
+//
+// This is a pure GRADIENT oracle (no ΔE): with an edge DOF, x = 0 means λ_e = 0
+// ⇒ spherical arc length = π (degenerate), so the path-integral-from-origin
+// energy reference is ill-defined — the gradient at a fixed non-degenerate x is
+// the unambiguous Finding-3 quantity.  It does NOT touch the spherical Hessian,
+// so it is unaffected by the Finding-4 edge-DOF Hessian guard.
+//
+// To regenerate: /tmp/oracle/SphereEdgeOracle.java.  Values are Java %.17g.
+// ─────────────────────────────────────────────────────────────────────────────
+TEST(SphericalGoldenJava, FullMeshEdgeDofGradient_Tetrahedron)
+{
+    constexpr double TWO_PI = 2.0 * 3.14159265358979323846264338328;
+    constexpr double PI_C   = 3.14159265358979323846264338328;
+    constexpr double SCALE  = 0.2;
+
+    auto mesh = make_tetrahedron();
+    auto maps = setup_spherical_maps(mesh);
+
+    for (auto e : mesh.edges()) {
+        auto h  = mesh.halfedge(e);
+        const auto& p1 = mesh.point(mesh.source(h));
+        const auto& p2 = mesh.point(mesh.target(h));
+        const double dx = p1.x()-p2.x(), dy = p1.y()-p2.y(), dz = p1.z()-p2.z();
+        maps.lambda0[e] = 2.0 * std::log(SCALE * std::sqrt(dx*dx + dy*dy + dz*dz));
+        maps.theta_e[e] = PI_C;
+        maps.e_idx[e]   = -1;
+    }
+
+    int idx = 0;
+    for (auto v : mesh.vertices()) { maps.v_idx[v] = idx++; maps.theta_v[v] = TWO_PI; }
+
+    auto pos = [&](Vertex_index v){ return mesh.point(v); };
+    auto same = [](const Point3& p, double X, double Y, double Z) {
+        return std::abs(p.x()-X)<1e-9 && std::abs(p.y()-Y)<1e-9 && std::abs(p.z()-Z)<1e-9;
+    };
+    // Edge connects positions (aX,aY,aZ)–(bX,bY,bZ) in either order?
+    auto connects = [&](Edge_index e, const double a[3], const double b[3]) {
+        auto h = mesh.halfedge(e);
+        const Point3& s = pos(mesh.source(h));
+        const Point3& t = pos(mesh.target(h));
+        return (same(s,a[0],a[1],a[2]) && same(t,b[0],b[1],b[2])) ||
+               (same(s,b[0],b[1],b[2]) && same(t,a[0],a[1],a[2]));
+    };
+    const double A[3]={1,1,1}, B[3]={1,-1,-1}, C[3]={-1,1,-1}, D[3]={-1,-1,1};
+
+    // Make edges A–B and C–D variable (replacement parameterization).
+    int edof = idx;  // edge DOFs start after the 4 vertex DOFs
+    Edge_index eAB, eCD;
+    for (auto e : mesh.edges()) {
+        if (connects(e, A, B)) { maps.e_idx[e] = edof++; eAB = e; }
+        else if (connects(e, C, D)) { maps.e_idx[e] = edof++; eCD = e; }
+    }
+    ASSERT_EQ(edof, 6);  // 4 vertex + 2 edge DOFs
+
+    auto u_of = [](const Point3& p){ return 0.10*p.x() - 0.07*p.y() + 0.13*p.z(); };
+
+    std::vector<double> x(6, 0.0);
+    for (auto v : mesh.vertices())
+        x[static_cast<std::size_t>(maps.v_idx[v])] = u_of(mesh.point(v));
+    // Edge DOF value = λ⁰_e + 0.1 (same perturbation as the Java oracle).
+    x[static_cast<std::size_t>(maps.e_idx[eAB])] = maps.lambda0[eAB] + 0.1;
+    x[static_cast<std::size_t>(maps.e_idx[eCD])] = maps.lambda0[eCD] + 0.1;
+
+    auto G = spherical_gradient(mesh, x, maps);
+
+    // Vertex gradients keyed by position.
+    struct VRow { double X, Y, Z, G; };
+    const VRow vg[4] = {
+        { 1,  1,  1, 2.5036751008175546},
+        { 1, -1, -1, 2.2303362601050205},
+        {-1,  1, -1, 1.8463710314817632},
+        {-1, -1,  1, 2.7499719487341570},
+    };
+    for (auto v : mesh.vertices()) {
+        const auto& p = mesh.point(v);
+        const double g = G[static_cast<std::size_t>(maps.v_idx[v])];
+        bool m = false;
+        for (auto& r : vg)
+            if (same(p, r.X, r.Y, r.Z)) { EXPECT_NEAR(g, r.G, 1e-12); m = true; break; }
+        EXPECT_TRUE(m);
+    }
+    // Edge gradients: A–B and C–D (Java golden values).
+    EXPECT_NEAR(G[static_cast<std::size_t>(maps.e_idx[eAB])], -0.35189517043413690, 1e-12);
+    EXPECT_NEAR(G[static_cast<std::size_t>(maps.e_idx[eCD])], -0.44101986058895950, 1e-12);
+}

code/tests/test_hyper_ideal_utility.cpp

@@ -4,10 +4,12 @@
 // Port of de.varylab.discreteconformal.functional.HyperIdealUtilityTest (Java/JUnit).
 
 #include "hyper_ideal_utility.hpp"
+#include "hyper_ideal_geometry.hpp"
 #include "clausen.hpp"
 
 #include <gtest/gtest.h>
 #include <cmath>
+#include <complex>
 
 using conformallab::calculateTetrahedronVolume;
 using conformallab::calculateTetrahedronVolumeWithIdealVertexAtGamma;
@@ -93,3 +95,43 @@ TEST(HyperIdealUtilityTest, CompareGeneralAndIdealFormulaCase2) {
     double V  = calculateTetrahedronVolume(bi, bj, bk, ai, aj, ak);
     EXPECT_NEAR(Ve, V, 1e-12);
 }
+
+// ─────────────────────────────────────────────────────────────────────────────
+// Golden-value oracle tests — pin the C++ pure-math core bit-for-bit against the
+// upstream Java reference (de.varylab.discreteconformal.functional.{Clausen,
+// HyperIdealUtility}), captured by running the compiled Java library (openjdk 17)
+// on these exact inputs.  Unlike the FD gradient checks (which only verify
+// curl-freeness, since the C++ energy is the path-integral of its own gradient),
+// these lock the absolute values of the math-critical helpers against an
+// independent implementation, catching any silent convention/formula drift.
+//
+// To regenerate: see doc/reviewer/java-port-audit.md (oracle harness recipe).
+// Values are Java's Double.toString output (shortest round-trip).  Tolerance is
+// 1e-12 (well above the ~1e-15 inter-platform libm divergence for these ranges).
+// ─────────────────────────────────────────────────────────────────────────────
+TEST(HyperIdealGoldenJava, ClausenLobachevskyImLi2) {
+    EXPECT_NEAR(conformallab::clausen2(0.7),  0.954448086482735,  1e-12);
+    EXPECT_NEAR(conformallab::clausen2(2.5),  0.4335982032355327, 1e-12);
+    EXPECT_NEAR(conformallab::clausen2(-1.3), -0.9897032532295984, 1e-12);
+    EXPECT_NEAR(Lobachevsky(0.9),             0.4121734067662043, 1e-12);
+    EXPECT_NEAR(conformallab::ImLi2(std::complex<double>(0.3, 0.4)),
+                                              0.46136289181910894, 1e-12);
+}
+
+TEST(HyperIdealGoldenJava, ZetaFamily) {
+    EXPECT_NEAR(conformallab::zeta13(0.5, 0.7, 0.9), 2.663195966482385,  1e-12);
+    EXPECT_NEAR(conformallab::zeta14(0.4, 0.8),      1.8262295633065202, 1e-12);
+    EXPECT_NEAR(conformallab::zeta15(0.6),           2.216976794676588,  1e-12);
+    EXPECT_NEAR(conformallab::zeta(0.5, 0.7, 0.9),   1.6156519307269948, 1e-12);
+}
+
+TEST(HyperIdealGoldenJava, TetrahedronVolumes) {
+    // Generic non-degenerate generalized hyperbolic tetrahedron.
+    EXPECT_NEAR(calculateTetrahedronVolume(0.6, 0.7, 0.8, 0.5, 0.9, 0.4),
+                2.9074633382516435, 1e-12);
+    // One ideal vertex at gamma, non-symmetric angles (Java test2 inputs).
+    EXPECT_NEAR(calculateTetrahedronVolumeWithIdealVertexAtGamma(
+                    0.6623267054958116, 1.437248992086214, 1.0420169560077686,
+                    0.6896178197389236, 0.5195634857410114, 0.6304500578493993),
+                2.0459750326926214, 1e-12);
+}