Finding-A from doc/reviewer/external-audit-2026-05-30.md.
Root cause: both the Java reference (HyperIdealFunctional.java:222-231)
and the C++ port silently applied the one-ideal-vertex volume formula
to the first ideal vertex found in a face, ignoring any additional ideal
vertices. For two or three ideal vertices this produces a wrong energy
value with no diagnostic.
Fix: add an ideal_count guard at the top of face_energy() that throws
std::logic_error for ideal_count >= 2. The one-ideal (Kolpakov-Mednykh)
and zero-ideal (Meyerhoff/Ushijima) paths are unchanged and correct.
Three new GTests cover the three guard cases:
MultiIdealGuard_TwoIdealVertices_Throws (two ideal → throw)
MultiIdealGuard_AllThreeIdealVertices_Throws (all ideal → throw)
MultiIdealGuard_ExactlyOneIdeal_DoesNotThrow (one ideal → no throw)
262/262 CGAL tests pass, 0 failed.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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