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>

src/CelerisLab/simulation.py

@@ -148,6 +148,7 @@ class Simulation:
                 from .body.motion import MovingCircle
                 obj.motion = MovingCircle((cx, cy), radius, translation,
                                           on_failure=self._fail_moving)
+                self.stepper.blocked = MOVING_BLOCKED
         elif type_lower == "sensor":
             from .body.geometry.circle import CircleGeometry
             cx, cy = float(center[0]), float(center[1])
@@ -171,10 +172,7 @@ class Simulation:
         if self._initialized:
             self.bodies.stage_add(obj)
             return -1
-        body_id = self.bodies.add(obj)
-        if translation is not None:
-            self._refresh_stepper_block()
-        return body_id
+        return self.bodies.add(obj)
 
     def add_jet(self, jet) -> int:
         """Register a body-independent Jet before ``initialize()``; returns its index.
@@ -214,10 +212,6 @@ class Simulation:
         # Device geometry is unknown after a failed moving step: same lifecycle as Jets.
         self._failed = f"moving circle step failed: {exc!r}"
 
-    def _refresh_stepper_block(self) -> None:
-        # Derived latch: direct stepper calls must not step after static-link exclusion.
-        self.stepper.blocked = MOVING_BLOCKED if self._moving_bodies() else None
-
     def _moving_bodies(self):
         return [obj for obj in self.bodies.objects if obj.motion is not None]
 
@@ -274,10 +268,7 @@ class Simulation:
         if self._initialized:
             self.bodies.stage_remove(id)
         else:
-            moving = self.bodies.get(id).motion is not None
             self.bodies.remove(id)
-            if moving:
-                self._refresh_stepper_block()
 
     # -- Legacy convenience (keep for backward compat) -----------------------
     def add_cylinder(self, center: Tuple[float, ...],
@@ -525,7 +516,7 @@ class Simulation:
             self.field, self._module, self.lbm_cfg,
         )
         self.stepper._step_count = _prev_step_count
-        self._refresh_stepper_block()
+        self.stepper.blocked = MOVING_BLOCKED if self._moving_bodies() else None
 
         self._assert_object_count_contract(expected_count=expected_n_objects)
 
@@ -552,7 +543,7 @@ class Simulation:
         # change. Compact-list construction publishes no outputs on failure.
         next_flags = self.bodies.build_flags(self.field.build_channel_flags())
         self._validate_moving_bodies()
-        self._refresh_stepper_block()
+        self.stepper.blocked = MOVING_BLOCKED if self._moving_bodies() else None
         if self.bodies.jets and self.bodies.count == 0:
             raise ValueError("Jets need bodies with cut links")
         self.bodies.build_compact_lists_for(self.bodies.objects, next_flags)

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: