Fixes crashes when Stop XR is pressed and when Kit is closed while Teleop is running

[hougantc-nvda]

Description

Before Kit tears down the OpenXR instance and session, we need to cleanup IsaacTeleop as the cached handles will become invalidated on Kit cleanup.

Stop XR: In the /xr/enabled callback, call _teardown_dead_session() instead of stop(). Only the session is torn down; pipeline and retargeting UI stay. step() then returns None (same as deferred start), the recording loop keeps rendering, and starting XR again works without restarting the script.

Kit close: Subscribe to GLOBAL_EVENT_PRE_SHUTDOWN with order=-100 so our cleanup runs before XRCore (order=0). We release our session and stop using our cached OpenXR handles before Kit XR tears down the OpenXR instance/session, avoiding use of invalid handles.

Fixes # (issue)

Type of change

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

Screenshots

Please attach before and after screenshots of the change if applicable.

Checklist

• I have read and understood the contribution guidelines
• I have run the pre-commit checks with ./isaaclab.sh --format
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• I have updated the changelog and the corresponding version in the extension's config/extension.toml file
• I have added my name to the CONTRIBUTORS.md or my name already exists there

[hougantc-nvda]

Rebased on top of #4746
That PR will need to be merged prior to this PR.

@rwiltz for vis

[greptile-apps]

Greptile Summary

This PR fixes crashes when Stop XR is pressed or Kit closes while Teleop is running by adding proper cleanup callbacks before OpenXR handles become invalidated.

Key changes:

• Subscribes to /xr/enabled setting to tear down the session (but not UI/pipeline) when XR is stopped, allowing seamless restart
• Subscribes to GLOBAL_EVENT_PRE_SHUTDOWN with order=-100 to ensure IsaacTeleop cleanup runs before Kit's XRCore tears down OpenXR resources
• Simplifies button polling to read directly from pipeline controller data

Critical issue found:

• The two new event subscriptions (_xr_enabled_subscription and _pre_shutdown_subscription) are never cleaned up, which will cause memory leaks if the TeleopSessionLifecycle object is recreated multiple times. A cleanup method should be added to unsubscribe these, similar to XrAnchorManager.cleanup() and CommandHandler.cleanup() patterns used elsewhere in the codebase.

Confidence Score: 3/5

• PR addresses critical crash bugs but introduces a resource leak that needs fixing
• The crash fixes are well-designed and properly sequenced (order=-100 ensures correct shutdown order), but the missing subscription cleanup is a legitimate resource management issue that could cause problems in production with repeated session creation
• source/isaaclab_teleop/isaaclab_teleop/session_lifecycle.py needs subscription cleanup added

Important Files Changed

Filename	Overview
source/isaaclab_teleop/isaaclab_teleop/session_lifecycle.py	Adds XR shutdown callbacks to prevent crashes, but subscriptions lack cleanup leading to potential memory leaks
source/isaaclab_teleop/isaaclab_teleop/isaac_teleop_device.py	Simplified button polling logic - no issues found

_{Last reviewed commit: f2e235c}

[greptile-apps]

_{4 files reviewed, 2 comments}

_{Edit Code Review Agent Settings | Greptile}

[hougantc-nvda]

Rebased on develop and ready to merge.