Fix Viser rendering for simulation axis markers

[yuecideng]

Description

This PR exports coordinate-frame markers created through SimulationManager.draw_marker() as backend-neutral frame overlays so they render in Viser with the correct world pose, axis length, and radius.

In headless Viser runs, native DexSim axis handles report is_visible() == False even when the marker was requested for display. The exporter now treats registered marker groups as visible until remove_marker() removes them, preventing target frames from being hidden while preserving marker lifecycle behavior.

Dependencies: None.

Issue: None.

Type of change

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

Screenshots

• Before: only the Viser /world coordinate frame was visible; simulation target markers were hidden.
• After: coordinated_placement.py displays both support-pan and placing-bread target frames at their expected poses.

Validation

• conda run -n open black --check --diff --color ./ — 904 files unchanged
• conda run -n open pytest -q tests/visualization/test_scene_exporter.py tests/visualization/test_viser_backend.py tests/sim/test_sim_manager.py — 48 passed
• conda run --no-capture-output -n open python scripts/tutorials/atomic_action/coordinated_placement.py --viser --viser-port 8769 --diagnose_plan — axis stage reached successfully
• Live Viser check — both target axes appeared, disappeared with the Frames toggle, and reappeared when enabled

Checklist

• I have run the black . command to format the code base.
• I have made corresponding changes to the documentation (not required for this internal backend fix).
• I have added tests that prove my fix is effective or that my feature works.
• Dependencies have been updated (not applicable).

[greptile-apps]

Greptile Summary

This PR exports active simulation axis markers as backend-neutral frame overlays so Viser can render their world pose and dimensions.

• Stores marker handles and display dimensions in a dedicated marker-group record.
• Generates collision-free frame-overlay IDs while preserving caller-provided overlays.
• Adds exporter and Viser backend coverage for marker rendering and ID collisions.

Confidence Score: 5/5

The PR appears safe to merge.

No blocking failure remains.

Important Files Changed

Filename	Overview
embodichain/lab/sim/sim_manager.py	Records active axis marker handles, arena ownership, and display dimensions for backend-neutral export.
embodichain/lab/visualization/scene_exporter.py	Converts registered axis markers into uniquely identified frame overlays and merges them with caller overlays.
tests/visualization/test_scene_exporter.py	Verifies headless marker export, pose and dimensions, and collision handling with caller-owned frame IDs.
tests/visualization/test_viser_backend.py	Verifies that marker frame overlays reach Viser with the expected path, pose, dimensions, and visibility.

_{Reviews (2): Last reviewed commit: "fix(visualization): avoid marker overlay..." | Re-trigger Greptile}