Follow-up to the Finding-A fix (face_energy guard). The throw is the
correct safe behaviour for now; the mathematically complete solution
requires formulas for semi-ideal and fully-ideal tetrahedra that are
absent from the Java reference.
Adds a structured research entry to research-track.md (Phase 9b+):
- primary references: Kolpakov-Mednykh arXiv:math/0603097, Milnor 1982,
Vinberg 1985
- acceptance criteria: two new volume functions + gradient-check tests +
limiting-behaviour continuity witness
- explicit note that the throw in face_energy() must not be removed
without implementing and testing the replacement formulas
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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