Stress-Testing the Preferred SO(10)-Compatible QDL Completion: Failure Modes, Alternatives, and Robustness

This record is Paper #3 in the QDL–SO10–1 benchmark sequence. It stress-tests the fixed SO(10)-compatible QDL benchmark introduced in Paper #1 and developed phenomenologically in Paper #2. The paper classifies which features of QDL–SO10–1 are robust, which are conditional, and which observations or calculations would force revision or falsification. It evaluates the benchmark against alternative simple-group completions, threshold sensitivity, proton-decay scaling, neutrino/baryogenesis perturbations, collider/remnant expectations, and explicit failure modes. This is a robustness-audit paper, not a complete global SO(10) scan, not an operator-level proton-decay calculation, not a completed leptogenesis computation, and not a final proof of uniqueness. Its purpose is to delimit the stability of the QDL–SO10–1 benchmark and make its failure conditions explicit.