test: follow the recursive _advance in three-level feed checks

baba5e0 replaced _advance_child with _advance(index, parent_buffer) driven
from _hop; the two feed-order tests still patched the removed method.
Patch _advance and record only index 2 (L1 hop feeding L2); assertions,
expected order and the stale-feed negative control are unchanged.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/validation/multigrid/test_refinement_three_level.py

@@ -80,11 +80,12 @@ class ThreeLevelCPU(unittest.TestCase):
         f, g = run._levels[1:]
         b = g.boundary
         events, feeds = [], []
-        advance, gather = run._advance_child, run._gather_halo
+        advance, gather = run._advance, run._gather_halo
-        def record_feed(buffer, **kw):
+        def record_feed(index, buffer, **kw):  # index 2: L1 hop feeds L2
+            if index == 2:
                 self.assertIs(buffer, (f.current, f.spare)[len(feeds)])
                 feeds.append(buffer)
-            advance(buffer, **kw)
+            advance(index, buffer, **kw)
         def record_halo(level, buffer, **kw):
             if level is g:
                 events.append(("halo", buffer))
@@ -95,7 +96,7 @@ class ThreeLevelCPU(unittest.TestCase):
             self.assertIs(kind, g.kind)
             events.append(("step", src))
         g.kernel.side_effect = record_step
-        with patch.object(run, "_advance_child", side_effect=record_feed), \
+        with patch.object(run, "_advance", side_effect=record_feed), \
                 patch.object(run, "_gather_halo", side_effect=record_halo):
             run.step()
         self.assertEqual(feeds, [f.current, f.spare])
@@ -105,8 +106,8 @@ class ThreeLevelCPU(unittest.TestCase):
         self.assertGreater(len(np.unique(b.tables["block"])), 1)
         # Negative control: reusing L1's old source at the midpoint must fail.
         feeds.clear()
-        with patch.object(run, "_advance_child", side_effect=lambda buffer, **kw:
+        with patch.object(run, "_advance", side_effect=lambda index, buffer, **kw:
-                          record_feed(f.current, **kw)):
+                          record_feed(index, f.current if index == 2 else buffer, **kw)):
             with self.assertRaises(AssertionError):
                 run.step()
         run.close()
@@ -172,11 +173,12 @@ class ThreeLevelGPU(unittest.TestCase):
             p1, p2 = run.patch, run.child_patch
             run.initialize(state(16, 16, 1), state(*p1.fine_shape, 2), state(*p2.fine_shape, 3))
             f = run._levels[1]
-            feeds, original = [], run._advance_child
+            feeds, original = [], run._advance
-            def record(buffer, **kw):
+            def record(index, buffer, **kw):  # index 2: L1 hop feeds L2
+                if index == 2:
                     feeds.append(int(buffer))
-                original(buffer, **kw)
+                original(index, buffer, **kw)
-            with patch.object(run, "_advance_child", side_effect=record):
+            with patch.object(run, "_advance", side_effect=record):
                 cur, spare = int(f.current), int(f.spare)
                 run.step(1)
             self.assertEqual(feeds, [cur, spare])  # current G, then the new G of hop 1