fix(test): tolerate boundary-tie in IVF distance_range assertions

rust/lance/src/index/vector/ivf/v2.rs

@@ -4318,17 +4318,41 @@ mod tests {
         // don't verify the number of results and row ids for hamming distance,
         // because there are many vectors with the same distance
         if dist_type != DistanceType::Hamming {
-            assert_eq!(left_res.num_rows(), part_idx);
-            assert_eq!(right_res.num_rows(), k - part_idx);
+            // Tolerate a single tied pair at the partition boundary. When
+            // dists[part_idx - 1] == part_dist, the strict-less left filter
+            // excludes both tied vectors and the inclusive right filter
+            // includes both, shifting one row from left to right and dropping
+            // row_ids[k - 1] off right_res's limit. Observed for Dot distance
+            // on ARM where SIMD FMA yields tied float32 dot products that x86
+            // does not. The distance-value assertions below still cover
+            // partition correctness in both cases.
+            let boundary_tie = part_idx > 0 && dists[part_idx - 1] == part_dist;
             let left_row_ids = left_res[ROW_ID].as_primitive::<UInt64Type>().values();
             let right_row_ids = right_res[ROW_ID].as_primitive::<UInt64Type>().values();
-            row_ids.iter().enumerate().for_each(|(i, id)| {
-                if i < part_idx {
-                    assert_eq!(left_row_ids[i], *id,);
-                } else {
-                    assert_eq!(right_row_ids[i - part_idx], *id,);
+            if boundary_tie {
+                assert_eq!(left_res.num_rows(), part_idx - 1);
+                for i in 0..(part_idx - 1) {
+                    assert_eq!(left_row_ids[i], row_ids[i]);
                 }
-            });
+                assert_eq!(right_res.num_rows(), k - part_idx);
+                // right_row_ids[0..2] are the two tied vectors in tiebreaker
+                // order; their identity is not pinned. right_row_ids[i] for
+                // i >= 2 aligns with row_ids[part_idx + i - 1] because the
+                // tie shifts one vector from left to right.
+                for i in 2..(k - part_idx) {
+                    assert_eq!(right_row_ids[i], row_ids[part_idx + i - 1]);
+                }
+            } else {
+                assert_eq!(left_res.num_rows(), part_idx);
+                assert_eq!(right_res.num_rows(), k - part_idx);
+                row_ids.iter().enumerate().for_each(|(i, id)| {
+                    if i < part_idx {
+                        assert_eq!(left_row_ids[i], *id,);
+                    } else {
+                        assert_eq!(right_row_ids[i - part_idx], *id,);
+                    }
+                });
+            }
         }
         let left_dists = left_res[DIST_COL].as_primitive::<Float32Type>().values();
         let right_dists = right_res[DIST_COL].as_primitive::<Float32Type>().values();