fix: validate compute_lon dimensions and domain bounds

src/lonkit/continuous/sampling.py

@@ -745,6 +745,9 @@ def compute_lon(
         >>> lon = compute_lon(sphere, dim=5, lower_bound=-5.0, upper_bound=5.0)
         >>> print(f"Found {lon.n_vertices} local optima")
     """
+    if isinstance(dim, bool) or not isinstance(dim, int | np.integer) or dim <= 0:
+        raise ValueError("dim must be a positive integer.")
+
     # Convert scalars to lists, leave sequences as-is
     lower_bounds: Sequence[float] = (
         [lower_bound] * dim if isinstance(lower_bound, int | float) else lower_bound
@@ -753,6 +756,15 @@ def compute_lon(
         [upper_bound] * dim if isinstance(upper_bound, int | float) else upper_bound
     )
 
+    lower_array = np.asarray(lower_bounds, dtype=float)
+    upper_array = np.asarray(upper_bounds, dtype=float)
+    if lower_array.shape != (dim,) or upper_array.shape != (dim,):
+        raise ValueError("lower_bound and upper_bound must each have exactly dim values.")
+    if not np.isfinite(lower_array).all() or not np.isfinite(upper_array).all():
+        raise ValueError("Domain bounds must be finite.")
+    if np.any(lower_array > upper_array):
+        raise ValueError("lower_bound must be <= upper_bound in every dimension.")
+
     domain = list(zip(lower_bounds, upper_bounds, strict=True))
 
     sampler = BasinHoppingSampler(config)

tests/continuous/test_sampling.py

@@ -5,10 +5,56 @@
 import pytest
 from scipy.optimize import OptimizeResult
 
-from lonkit import BasinHoppingSampler, BasinHoppingSamplerConfig
+from lonkit import BasinHoppingSampler, BasinHoppingSamplerConfig, compute_lon
 from tests.conftest import DOMAIN_2D, SEED, sphere
 
 
+class TestComputeLonDomain:
+    @pytest.mark.parametrize(
+        "dim, lower, upper, message",
+        [
+            (0, -1, 1, "positive integer"),
+            (-1, -1, 1, "positive integer"),
+            (1.5, -1, 1, "positive integer"),
+            (True, -1, 1, "positive integer"),
+            (2, [0], [1], "exactly dim"),
+            (2, [0, 0], [1], "exactly dim"),
+            (2, [0], 1, "exactly dim"),
+            (2, [[0, 0]], [[1, 1]], "exactly dim"),
+            (2, -np.inf, 1, "finite"),
+            (2, 0, [1, np.inf], "finite"),
+            (2, [0, np.nan], 1, "finite"),
+            (2, [0, 2], [1, 1], "lower_bound must be <="),
+        ],
+    )
+    def test_invalid_domain_fails_before_sampling(self, dim, lower, upper, message):
+        with patch.object(BasinHoppingSampler, "sample") as sample:
+            with pytest.raises(ValueError, match=message):
+                compute_lon(sphere, dim, lower, upper)
+            sample.assert_not_called()
+
+    @pytest.mark.parametrize(
+        "lower, upper",
+        [(-1, 1), ([-1, 0], [1, 0]), (np.array([-1, -1]), 1)],
+    )
+    def test_valid_domain_preserves_dimension(self, lower, upper):
+        dimensions = []
+
+        def objective(x):
+            dimensions.append(len(x))
+            return sphere(x)
+
+        lon = compute_lon(
+            objective,
+            2,
+            lower,
+            upper,
+            config=BasinHoppingSamplerConfig(n_runs=1, max_iter=1, seed=SEED),
+        )
+        assert dimensions and set(dimensions) == {2}
+        assert lon.n_vertices > 0
+
+
 class TestHashSolution:
     @pytest.mark.parametrize("precision", [0, 1, 2, 3])
     def test_small_positive_and_negative_values_hash_equally(self, precision: int) -> None: