fix(webclient): fix XR panel snapping to face away from user when moved

[yanziz-nvidia]

Closes #546

Summary

• Bug 1 (yaw accuracy): The old code used setFromUnitVectors(zAxis, dir3D) + setFromQuaternion('YXZ') to extract horizontal yaw. Because dir3D included the camera's height offset, the extracted Euler Y was not the true horizontal yaw. Replaced with Math.atan2(dx, dz) on the XZ plane.
• Bug 2 (±π wrap): The face-camera damp() call had no angle wrapping. When the target yaw crossed the ±π boundary, damp() took the ~2π wrong-way path, spinning the panel to face backward. Normalized diff to [-π, π] before calling damp().
• Bug 3 (Handle quaternion reset — root cause of 90° snap after drag): @pmndrs/handle's defaultApply copies state.current.quaternion to the target on every drag frame (useFrame priority -1, before face-camera at priority 0) and again on drag release. With rotate={false}, that quaternion is always the one captured at drag-start, so it continuously reset the face-camera rotation mid-drag and wiped it entirely on release — snapping the panel up to 90° off after every drag. Fixed by passing a custom apply function (applyPositionSkipRotation) to Handle that copies only position, leaving quaternion/rotation entirely under face-camera control.

Test plan

• Enter XR session and drag the panel to the left or right — panel should rotate to face you as it moves
• Release the handle — panel should stay facing you, not snap back to a wrong angle
• Move/walk around the panel in the emulator — panel should track you continuously
• Walk behind the panel — it should smoothly rotate to re-face you
• Verify normal forward-facing behaviour is unchanged when standing still

🤖 Generated with Claude Code

[coderabbitai]

📝 Walkthrough

Walkthrough

CloudXRUI.tsx refactors the face-camera rotation implementation to remove quaternion and Euler conversions. The module now imports only essential Three.js types, retains position-vector helpers for computing projected coordinates on the XZ plane, and directly computes target yaw using atan2 from those projections. Angular deltas are normalized to the range [-π, π] for shortest-path interpolation, and the group rotation is dampened toward the computed target, replacing the prior quaternion-to-Euler (YXZ) extraction logic.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title accurately describes the main fix: addressing XR panel snapping away from the user when moved, which is the core issue resolved in the PR.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/webclient-panel-face-away-snap

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[yanziz-nvidia]

See https://nvidia.github.io/IsaacTeleop/preview/pr-629/client/#/sim

[gareth-morgan-nv]

LGTM. Maybe add a test?