fix+test: Euclidean holonomy/τ end-to-end + spherical edge-DOF oracle (2026-05-29 audit)

Bundles the 2026-05-29 Java↔C++ math-correctness audit (doc/reviewer/
java-port-audit.md, 11 findings) with two follow-up fixes.

Audit code changes:
- Finding 3 (spherical_functional): edge-DOF replacement parameterization via
  spher_eff_lambda; edge gradient α_opp⁺+α_opp⁻−θ_e (drops additive −(S⁺+S⁻)/2)
- Finding 4 (spherical_hessian): always-compiled edge-DOF throw guard
- Finding 6 (period_matrix): faithful normalizeModulus (0≤Re≤½, Im≥0, |τ|≥1)
- Finding 9 (inversive_distance): degenerate-face limiting angles, no skip
- Findings 1/2 (euclidean): degenerate gradient limiting angles + Hessian guard

Euclidean holonomy/τ fix: develop the cut surface across the dual spanning tree
only (cut_graph now exposes is_dual_tree), so genus-1 cut edges yield
non-degenerate lattice generators. Previously τ came out 0 / NaN / 1e13 on the
bundled tori; now matches the analytic revolution modulus i·√(R²−r²)/r. Re-enabled
τ reporting in the Euclidean CLI; rewrote validation.md §3/§4 accordingly.

Tests (240 CGAL, 0 skipped):
- HolonomyEndToEnd ×3 — tori of revolution (4×4, hex 6×6, 8×8) vs analytic modulus
- SphericalFunctional.EdgeGradient_RegularTetClosedForm — independent closed-form
  π/3 oracle locking the Finding-3 edge formula (the path-integral FD check cannot
  detect a wrong-but-conservative gradient)

Also documents the latent spherical/hyperbolic holonomy-extraction bug (same
single-development pattern, dead code today) in research-track.md (Phase 9c/10),
and adds favour/normalisations to the codespell ignore list.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

code/include/period_matrix.hpp

@@ -41,6 +41,7 @@
 //   std::complex<double> reduce_to_fundamental_domain(τ)  — apply SL(2,ℤ)
 
 #include "layout.hpp"
+#include "discrete_elliptic_utility.hpp"   // normalizeModulus (Java-faithful)
 #include <complex>
 #include <cmath>
 #include <vector>
@@ -129,8 +130,14 @@ inline bool is_in_fundamental_domain(std::complex<double> tau, double tol = 1e-9
 // For genus-1 surfaces, also reduces τ to the fundamental domain.
 // ─────────────────────────────────────────────────────────────────────────────
 /// Compute the period data from the Euclidean holonomy translations.
-/// For genus 1, also reduces `τ` to the SL(2,ℤ) fundamental domain
-/// when `reduce` is `true` (default).
+/// For genus 1, also normalises `τ` when `reduce` is `true` (default)
+/// using `normalizeModulus` — the Java-faithful reduction
+/// (`DiscreteEllipticUtility.normalizeModulus`), which folds τ into
+/// `0 ≤ Re(τ) ≤ ½`, `Im(τ) ≥ 0`, `|τ| ≥ 1` (the extra `Re ≥ 0` fold
+/// uses the mirror symmetry `τ ≅ −τ̄`).  This matches the upstream Java
+/// output exactly (Finding 6).  For the canonical SL(2,ℤ) domain
+/// (`−½ ≤ Re τ < ½`, no mirror fold) call `reduce_to_fundamental_domain`
+/// on `pd.tau` instead.
 inline PeriodData compute_period_matrix(const HolonomyData& hol, bool reduce = true)
 {
     PeriodData pd;
@@ -156,7 +163,9 @@ inline PeriodData compute_period_matrix(const HolonomyData& hol, bool reduce = t
     if (tau.imag() < 0.0) return pd;      // degenerate
 
     if (reduce) {
-        tau = reduce_to_fundamental_domain(tau);
+        // Java-faithful normalisation (Finding 6): folds τ into
+        // 0 ≤ Re ≤ ½, Im ≥ 0, |τ| ≥ 1 via DiscreteEllipticUtility.normalizeModulus.
+        tau = normalizeModulus(tau);
         pd.in_fundamental_domain = true;
     }
     pd.tau = tau;