Migrate current callers to level-indexed refinement API

tests/unit/test_refinement_mrt.py

@@ -31,7 +31,10 @@ class RefinementMRTHost(unittest.TestCase):
                      "compute_feq(rho, ux, uy, feq);",
                      "collide_srt_no_force(f, feq, d_params.omega);"):
             self.assertIn(text, block_collision)
-        self.assertIn("collide_srt(f, feq, forcing, omega);", channel)
+        self.assertIn("collide_srt(f, feq, forcing, omega);", block_collision)
+        self.assertIn("#elif BLOCK_ROOT_BC == 2", block_collision)
+        self.assertEqual(channel.count("block_collide(f);"), 1)
+        self.assertNotIn("collide_mrt_unforced(f);", channel)
         for source in (blocks,):
             self.assertIn("(COLLISION_MODEL != 0 && COLLISION_MODEL != 2)", source)
             self.assertIn("USE_LES", source)
@@ -40,7 +43,7 @@ class RefinementMRTHost(unittest.TestCase):
         # One shared unforced MRT body; each blocked/patch path calls it exactly once.
         mrt = (KERNELS / "operators/collision_mrt.cuh").read_text()
         self.assertEqual(mrt.count("void collide_mrt_unforced("), 1)
-        for source in (blocks + "\n" + block_collision, channel):
+        for source in (blocks + "\n" + block_collision, channel + "\n" + block_collision):
             self.assertEqual(source.count("collide_mrt_unforced(f);"), 1)
             self.assertNotIn("collide_mrt_no_force(", source)
             self.assertNotIn("compute_rho_u(f, rho, ux, uy);\n            collide_mrt", source)