fix(disagg): correct DSA/SWA state-page transfer mismatch in PD disaggregation (#27004)

test/registered/unit/disaggregation/test_disaggregation_wire.py

@@ -3,6 +3,7 @@ import unittest
 import numpy as np
 
 from sglang.srt.disaggregation.common.utils import (
+    group_concurrent_contiguous,
     pack_int_lists,
     pack_list_of_buffers,
     unpack_int_lists,
@@ -45,5 +46,49 @@ class TestDisaggregationWire(unittest.TestCase):
         self.assertEqual(unpack_list_of_buffers(pack_list_of_buffers(bufs)), bufs)
 
 
+class TestGroupConcurrentContiguous(unittest.TestCase):
+    @staticmethod
+    def _arr(values):
+        return np.array(values, dtype=np.int32)
+
+    def test_single_contiguous_group(self):
+        src = self._arr([10, 11, 12])
+        dst = self._arr([5, 6, 7])
+        self.assertEqual(
+            group_concurrent_contiguous(src, dst),
+            ([[10, 11, 12]], [[5, 6, 7]]),
+        )
+
+    def test_splits_on_discontiguous_indices(self):
+        src = self._arr([10, 11, 20])
+        dst = self._arr([5, 6, 7])
+        self.assertEqual(
+            group_concurrent_contiguous(src, dst),
+            ([[10, 11], [20]], [[5, 6], [7]]),
+        )
+
+    def test_both_empty(self):
+        self.assertEqual(
+            group_concurrent_contiguous(self._arr([]), self._arr([])), ([], [])
+        )
+
+    def test_empty_src_nonempty_dst(self):
+        self.assertEqual(
+            group_concurrent_contiguous(self._arr([]), self._arr([1, 2])), ([], [])
+        )
+
+    def test_nonempty_src_empty_dst(self):
+        # Regression: a non-empty source paired with an empty destination must not
+        # raise a NumPy broadcast error (observed transferring DSA sparse-attention
+        # state on a disaggregated GLM deployment when decode registered zero dst indices).
+        self.assertEqual(
+            group_concurrent_contiguous(self._arr([1, 2]), self._arr([])), ([], [])
+        )
+
+    def test_mismatched_nonempty_lengths_raise(self):
+        with self.assertRaises(ValueError):
+            group_concurrent_contiguous(self._arr([1, 2, 3]), self._arr([1, 2]))
+
+
 if __name__ == "__main__":
     unittest.main()