test: dense/blocked parity rows for MRT bodies and two fine bodies

Extends DenseBlockedRouteParity (test-only, on 1573942) with the residual
dense-supported combinations named before any dense-route deletion:
- test_mrt_bodies: MRT on a periodic root with a passive circle, an
  actuated circle (+/-) and a velocity Jet with an amplitude switch
  (MRT slot/reservoir is rejected on every route: on_site_velocity is
  SRT-only);
- test_two_bodies: two circles on a wider patch (4, 4, 28, 20), periodic
  and slot/reservoir, Jet on one + passive other, and two actuated (+/-);
  routes D/D, D/B [None, (8, 8)], B/B [(12, 8), (8, 8)].
Same gate: exact FP32 bits and NaN masks at 0, 1, 2, 8 and after
re-initialize; D/B vs B/B raw-exchange ledgers equal for every body.
Docstring table updated; no tolerance, no src change.

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

tests/validation/multigrid/test_refinement_blocked_base.py

@@ -23,13 +23,16 @@ Route capabilities (rejections checked before CUDA by test_route_capability_matr
   channel root                                  rejected  rejected  yes
   several L1 rectangles                         rejected  rejected  yes
   depth >= 3 with a dense level                 rejected  rejected  yes
+  MRT, periodic root, circle/actuation/Jet      yes       yes       yes   (parity gate)
+  two fine bodies (Jet + passive, two actuated) yes       yes       yes   (parity gate)
+  MRT with slot/reservoir root                  rejected on every route (on_site_velocity is SRT-only)
 Slot/reservoir walls are compile-time WALL_* macros on a dense root and the
 d_block_wall constant on a blocked root: BC-encoding parity, bit-identical by
 this gate. Dense fine bodies use CurvedLinkSoA + CurvedBoundaryKernel
 (n_objects > 0), blocked ones BlockCurvedBoundary; same links and physics,
-compared through the population rows. Parked here: MRT (covered by
-test_refinement_mrt_gpu::test_dense_versus_blocked_mrt_two_level), shifted and
-depth >= 3 (no dense route to compare), several bodies (later slice).
+compared through the population rows. MRT body-free is also covered by
+test_refinement_mrt_gpu::test_dense_versus_blocked_mrt_two_level. Parked:
+shifted and depth >= 3 (no dense route to compare).
 """
 from contextlib import ExitStack, contextmanager, nullcontext
 from dataclasses import replace
@@ -354,6 +357,25 @@ class BlockedBaseGPU(unittest.TestCase):
 
 
 ROUTES = (("D/D", [None, None]), ("D/B", [None, FINE_BLOCK]), ("B/B", [(12, 8), FINE_BLOCK]))
+# Two-body rows: patch (4, 4, 28, 20) gives a 40 x 56 fine window, tiled (8, 8).
+WIDE_BOUNDS = (4, 4, 28, 20)
+WIDE_ROUTES = (("D/D", [None, None]), ("D/B", [None, (8, 8)]), ("B/B", [(12, 8), (8, 8)]))
+LEFT, RIGHT, RADIUS = (12.0, 12.0), (20.0, 12.0), 2.15
+
+
+def body(ident, center, spec=None):
+    from CelerisLab.body.geometry.circle import CircleGeometry
+    from CelerisLab.body.objects import SimObject
+    return SimObject(ident, geometry=CircleGeometry(*center, RADIUS), center=center, radius=RADIUS,
+                     surface_actuation=spec)
+
+
+TWO_BODY_CASES = (
+    ("jet + passive", lambda: [body(0, LEFT), body(1, RIGHT)],
+     lambda: [actuation(SPEED).as_jet(LEFT, RADIUS)], -SPEED),
+    ("actuated +/-", lambda: [body(0, LEFT, actuation(SPEED)), body(1, RIGHT, actuation(-SPEED))],
+     lambda: [], None),
+)
 
 
 def same_summary(a, b):
@@ -414,17 +436,18 @@ def replace_value(tree, path, value=None):
 class DenseBlockedRouteParity(unittest.TestCase):
     """D/D vs D/B vs B/B, unshifted SRT, one circle or one velocity Jet; see module docstring."""
 
-    def run_routes(self, mode, objects=(), jets=(), switch=None):
+    def run_routes(self, mode, objects=(), jets=(), switch=None, cfg=None, bounds=BOUNDS, routes=ROUTES):
         from CelerisLab.cuda.context import CudaContext
-        cfg = config(mode)
-        p = FixedPatch2D.from_config(cfg, BOUNDS)
+        cfg = cfg or config(mode)
+        p = FixedPatch2D.from_config(cfg, bounds)
         arrays = state(NY, NX, 1), state(*p.fine_shape, 2)
+        bodies = sorted({obj.obj_id for obj in objects})
         results = {}
         with CudaContext(0) as context:
-            for name, blocks in ROUTES:
+            for name, blocks in routes:
                 observe = bool(objects) and blocks[1] is not None
                 snapshots, ledgers = [], []
-                with FixedPatchStepper(cfg, context=context, coarse_boundary=mode, refinements=[BOUNDS],
+                with FixedPatchStepper(cfg, context=context, coarse_boundary=mode, refinements=[bounds],
                                        level_blocks=blocks, level_objects=[(), tuple(objects)],
                                        level_jets=[(), tuple(jets)],
                                        observe_raw_exchange=observe) as backend:
@@ -435,7 +458,8 @@ class DenseBlockedRouteParity(unittest.TestCase):
                         backend.step(step - backend.step_count)
                         snapshots.append(backend.download() + raw(backend))
                         if observe and step:
-                            ledgers.append(tuple(backend.read_raw_exchange(0, window=window)
+                            ledgers.append(tuple(backend.read_raw_exchange(body, window=window)
+                                                 for body in bodies
                                                  for window in ("last_base_step", "last_substep")))
                     backend.initialize(*arrays)
                     snapshots.append(backend.download() + raw(backend))
@@ -475,6 +499,24 @@ class DenseBlockedRouteParity(unittest.TestCase):
             self.check(f"{mode} jet switch",
                        self.run_routes(mode, objects=[circle()], jets=[jet()], switch=-SPEED))
 
+    def test_mrt_bodies(self):
+        """MRT, periodic root (on_site_velocity slot/reservoir is SRT-only on every route)."""
+        cfg = replace(config("periodic"), collision="MRT")
+        for label, objects, jets, switch in (("circle", [circle()], (), None),
+                                             ("actuated +", [circle(actuation(SPEED))], (), None),
+                                             ("actuated -", [circle(actuation(-SPEED))], (), None),
+                                             ("jet switch", [circle()], [jet()], -SPEED)):
+            self.check(f"MRT periodic {label}",
+                       self.run_routes("periodic", objects, jets, switch, cfg=cfg))
+
+    def test_two_bodies(self):
+        """Two circles on a wider patch (same tiles on every route): Jet + passive, two actuated."""
+        for mode in ("periodic", "slot_reservoir"):
+            for label, objects, jets, switch in TWO_BODY_CASES:
+                self.check(f"{mode} two bodies {label}",
+                           self.run_routes(mode, objects(), jets(), switch, bounds=WIDE_BOUNDS,
+                                           routes=WIDE_ROUTES))
+
 
 if __name__ == "__main__":
     unittest.main()