tests: recompile installs a guarded stepper; refused close keeps failed state

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

tests/unit/test_moving_bodies.py

@@ -232,6 +232,32 @@ def test_add_body_and_set_body_route_targets(monkeypatch):
                          **kwargs)
 
 
+def test_recompile_installs_a_guarded_stepper(monkeypatch):
+    from CelerisLab.lbm.stepper import LBMStepper
+    sim = routed_simulation(monkeypatch)
+    sim.add_body("circle", (50., 40.), 10., translation=Translation((0., 0., -1., 1.), .1))
+    launches = []
+    kernel_module = SimpleNamespace(get_function=lambda name: lambda *a, **k: launches.append(name))
+    monkeypatch.setattr(module.compiler, "build_module", lambda *a, **k: kernel_module)
+    sim.lbm_cfg = SimpleNamespace(validate_runtime=lambda: None, viscosity=.01, omega=1.,
+                                  streaming="double_buffer", threads_per_block=128,
+                                  is_d2q9=True, nx=120, ny=80, nz=1)
+    sim._compiled_viscosity = .01
+    sim._assert_allocation_contract = lambda: None
+    sim._resolve_compile_arch = lambda: "sm_70"
+    sim._assert_object_count_contract = lambda **k: None
+    sim.field = SimpleNamespace(module=None, invalidate_module_constant_cache=lambda: None,
+                                _upload_params=lambda: None, _runtime_params={},
+                                ddf_gpu="ddf", temp_gpu="temp", n_curved=0)
+    sim.stepper = SimpleNamespace(_step_count=7, blocked=None)
+    sim._recompile()
+    assert isinstance(sim.stepper, LBMStepper) and sim.stepper.step_count == 7
+    with pytest.raises(RuntimeError, match="moving kernels"):
+        sim.stepper.step(1, action_gpu=None, obs_gpu=None)
+    assert launches == [] and (sim.field.ddf_gpu, sim.field.temp_gpu) == ("ddf", "temp")
+    assert sim.stepper.step_count == 7
+
+
 def test_stepper_latch_follows_moving_bodies(monkeypatch):
     sim = routed_simulation(monkeypatch)
     still = sim.add_body("circle", (100., 40.), 5.)
@@ -315,6 +341,11 @@ def test_failed_moving_step_marks_simulation_failed(monkeypatch):
             call()
     with pytest.raises(RuntimeError, match="unknown"):  # no retry on the failed circle
         motion.advance(lambda *_: None, lambda: None, lambda: None)
-    sim.close()  # close still works
+    with sim.ctx.activate():  # a refused close keeps the failed state and resources
+        with pytest.raises(RuntimeError, match="active CUDA"):
+            sim.close()
+    assert sim._failed is not None and sim.bodies is not None and not sim._closed
+    sim.close()  # retry outside the activation succeeds
+    assert sim._closed and sim._failed is not None
     with pytest.raises(RuntimeError, match="Simulation failed"):  # no re-entry after close
         sim.run(1)