simulation: revert latch-only refresh (e682d16, 36eac713)

No reachable path leaves a stale latch (Grok review): initialize and
_recompile recompute it, and post-init removal of a translating circle
cannot commit. simulation.py is back to b448bc3f; the latch-only test is
dropped. The recompile, close-retry and tightened after-close tests stay.

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

tests/unit/test_moving_bodies.py

@@ -258,16 +258,6 @@ def test_recompile_installs_a_guarded_stepper(monkeypatch):
     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.)
-    assert sim.stepper.blocked is None
-    moving = sim.add_body("circle", (50., 40.), 10., translation=Translation((0., 0., -1., 1.), .1))
-    assert sim.stepper.blocked is not None
-    sim.remove_body(moving)  # removing the last translating circle clears the latch
-    assert sim.stepper.blocked is None and sim.bodies.get(still).motion is None
-
-
 def validate(monkeypatch, objects, flags=None, **cfg):
     sim = routed_simulation(monkeypatch)
     for obj in objects: