Gate action upload on Jet stationarity; document setter device-error handling

ObjectManager._upload_action_async is the single entry for every action
path (setters, direct edits of the public action array, run()). It now
also rejects nonzero vx/vy/omega slots of Jet-driven bodies via
validate_jet_motion, before any device copy. Regression: each motion
slot edited directly is rejected with no device write; zero motion
uploads. Simulation.set_jet_amplitude documents that a device error
requires close/recreate, as for other CUDA exceptions.

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

tests/unit/test_jets.py

@@ -253,6 +253,23 @@ def test_set_body_rejects_motion_of_jet_driven_body(device):
     bodies.set_body_state(0, omega=0.)
 
 
+def test_action_upload_rejects_motion_of_jet_driven_body(device):
+    # Direct edits of the public action array are checked at the upload gate.
+    jet = Jet(Sector(CENTER, 0., .6, 3.), Radial(CENTER, inward=False), "quartic", 2e-3)
+    field, bodies = jet_case(device, [jet])
+    stream = SimpleNamespace(synchronize=lambda: None)
+    slot = 3*field.cfg.dim
+    for index in (0, 1, slot - 1):  # vx, vy, omega
+        bodies.action[:] = 0
+        bodies.action[index] = .01
+        writes = device.writes
+        with pytest.raises(ValueError, match="stationary"):
+            bodies._upload_action_async(stream)
+        assert device.writes == writes  # nothing reached the device
+    bodies.action[:] = 0
+    bodies._upload_action_async(stream)  # zero motion stays accepted
+
+
 def test_fine_boundary_keeps_edge_frame_hits_and_checks_jets():
     from CelerisLab.body.objects import SimObject
     from CelerisLab.body.geometry.circle import CircleGeometry