test: stabilize coordinate permutation oracle

tests/test_whitened_svd_oracles.py

@@ -189,7 +189,10 @@ def test_feature_coordinate_permutation_round_trips_through_inverse_mapping() ->
     feature_permutation = torch.tensor([2, 0, 3, 1])
     extractor = WhitenedSVDExtractor(
         regularization_eps=REGULARIZATION_EPS,
-        min_variance_ratio=0.0,
+        # The fixture has one mathematically null covariance dimension. Apply
+        # the production-default truncation policy so this metamorphic oracle
+        # compares the well-defined retained subspace across LAPACK backends.
+        min_variance_ratio=0.01,
     )
 
     original = extractor.extract(_as_public_samples(harmful), _as_public_samples(harmless), 3)