Fix PhysX simulation lifecycle ownership (#6588)

# Description

PR #6505 removed the Kit extension startup that previously re-imported
`isaaclab_physx` after Kit loaded. When task configuration imports the
PhysX package before Kit, the compatibility hook returns early and is
never retried. The original Isaac Sim `SimulationManager` STOP callback
then invalidates the tensor view shared with `PhysxManager`, causing
Franka and other PhysX articulation environments to fail during their
first reset.

This PR retries the existing idempotent compatibility takeover from
`PhysxManager.initialize()`, where Kit is available and PhysX is the
selected backend. It also updates the import-order contract and adds an
integration regression test that imports `PhysxCfg` before launching
Kit.

This fix is independent of #6337.

## Type of change

- Bug fix (non-breaking change which fixes an issue)
- Documentation update

## Screenshots

N/A

## Validation

- Regression RED on unmodified develop: module alias remained the
original Isaac Sim `SimulationManager` after `SimulationContext`
initialization.
- Regression GREEN: `1 passed`.
- `Isaac-Reach-Franka`, 16 environments, PhysX: environment creation,
reset, and first step completed with exit code 0 and without
invalidated-view errors.
- `./isaaclab.sh -p tools/changelog/cli.py check develop`
- `./isaaclab.sh -f`

## Checklist

- [x] I have read and understood the contribution guidelines
- [x] I have run the pre-commit checks with `./isaaclab.sh -f`
- [x] I have made corresponding changes to the documentation
- [x] My changes generate no new warnings
- [x] I have added tests that prove the fix is effective
- [x] I have added a changelog fragment for every touched package
- [x] My name already exists in `CONTRIBUTORS.md`

Author: AntoineRichard

source/isaaclab_physx/changelog.d/antoiner-physx-simulation-manager-lifecycle.rst

@@ -0,0 +1,5 @@
+Fixed
+^^^^^
+
+* Fixed PhysX tensor views being invalidated when the PhysX backend configuration
+  was imported before Kit startup.

source/isaaclab_physx/isaaclab_physx/__init__.py

@@ -49,13 +49,11 @@ def _patch_isaacsim_simulation_manager():
 
     This function is intentionally lazy: it only patches if
     ``isaacsim.core.simulation_manager`` is already present in ``sys.modules``.
-    In the normal production flow Kit loads that module during extension startup,
-    before any user script imports :mod:`isaaclab_physx`, so the condition is
-    true and the patch fires on time. If :mod:`isaaclab_physx` happens to be
-    imported for pure config loading before Kit has launched (e.g. in
-    ``test_env_cfg_no_forbidden_imports``), the module is absent and this
-    function is a no-op — which is correct, because no callbacks have been
-    registered yet.
+    Config loading may import :mod:`isaaclab_physx` before Kit has launched. In
+    that case, the module is absent and this function is a no-op because no
+    callbacks have been registered yet. :meth:`PhysxManager.initialize` invokes
+    this function again after Kit startup, guaranteeing that the original
+    callbacks are disabled before Isaac Lab creates PhysX tensor views.
     """
     original_module = sys.modules.get("isaacsim.core.simulation_manager")
     if original_module is None:

source/isaaclab_physx/isaaclab_physx/physics/physx_manager.py

@@ -285,6 +285,10 @@ def __getattr__(self, name: str) -> Callable[..., Any]:
     @classmethod
     def initialize(cls, sim_context: SimulationContext) -> None:
         """Initialize the physics manager."""
+        from isaaclab_physx import _patch_isaacsim_simulation_manager
+
+        _patch_isaacsim_simulation_manager()
+
         from isaaclab.sim.utils.stage import get_current_stage_id
 
         super().initialize(sim_context)

source/isaaclab_physx/test/sim/test_simulation_manager_ownership.py

@@ -0,0 +1,45 @@
+# Copyright (c) 2022-2026, The Isaac Lab Project Developers (https://github.com/isaac-sim/IsaacLab/blob/main/CONTRIBUTORS.md).
+# All rights reserved.
+#
+# SPDX-License-Identifier: BSD-3-Clause
+
+"""Verify PhysX lifecycle ownership when its package is imported before Kit starts."""
+
+from isaaclab_physx.physics import PhysxCfg
+
+from isaaclab.app import AppLauncher
+from isaaclab.test.utils import resolve_test_sim_device
+
+# Launch Kit only after importing the PhysX config to reproduce normal entry-point config resolution.
+simulation_app = AppLauncher(headless=True, device=resolve_test_sim_device()).app
+
+import pytest
+from isaaclab_physx.physics import PhysxManager
+
+import isaacsim.core.simulation_manager as simulation_manager_module
+
+import isaaclab.sim as sim_utils
+from isaaclab.sim import SimulationCfg, SimulationContext
+
+pytestmark = pytest.mark.integration
+
+
+@pytest.fixture(autouse=True)
+def setup_teardown():
+    """Create a fresh stage and simulation context for each test."""
+    SimulationContext.clear_instance()
+    sim_utils.create_new_stage()
+    yield
+    SimulationContext.clear_instance()
+
+
+@pytest.mark.isaacsim_ci
+def test_initialize_claims_simulation_manager_lifecycle():
+    """PhysxManager initialization disables Isaac Sim's original lifecycle callbacks."""
+    original_manager = simulation_manager_module.SimulationManager
+    assert original_manager is not PhysxManager
+
+    SimulationContext(cfg=SimulationCfg(physics=PhysxCfg()))
+
+    assert simulation_manager_module.SimulationManager is PhysxManager
+    assert not any(original_manager.get_default_callback_status().values())