feat(hicache): Use NIXL path-mode (#27060)

test/registered/unit/mem_cache/test_hicache_nixl_storage.py

@@ -382,17 +382,36 @@ class TestNixlUnified(CustomTestCase):
                 num_pages * mock_host.page_size, dtype=torch.int64
             )
 
+            # Distinct data per key so a round trip that mixes keys up (e.g. a
+            # FILE registration that collapses every desc onto one file) is
+            # caught, not just the pass/fail return codes. Non-zero-copy only:
+            # the layer_first layout makes per-page seeding straightforward.
+            if not is_zero_copy_mode:
+                ps = mock_host.page_size
+                for p in range(num_pages):
+                    mock_host.kv_buffer[:, :, p * ps : (p + 1) * ps] = float(p + 1)
+                expected = mock_host.kv_buffer.clone()
+
             set_results = hicache.batch_set_v1(keys, host_indices)
             self.assertTrue(
                 all(set_results),
                 f"batch_set_v1 failed (zero_copy={is_zero_copy_mode}): {set_results}",
             )
 
+            if not is_zero_copy_mode:
+                mock_host.kv_buffer.zero_()
+
             get_results = hicache.batch_get_v1(keys, host_indices)
             self.assertTrue(
                 all(get_results),
                 f"batch_get_v1 failed (zero_copy={is_zero_copy_mode}): {get_results}",
             )
+
+            if not is_zero_copy_mode:
+                self.assertTrue(
+                    torch.equal(mock_host.kv_buffer, expected),
+                    "round trip corrupted or mixed up per-key data",
+                )
         finally:
             agent.get_reg_descs = orig_get_reg
             agent.register_memory = orig_register