Add regression test for fabrics after rebuild

[alexmillane]

Summary

Adds a test that tests fabric poses of prims after a stage rebuild.

Detailed description

• The tests: [Bug Report] Rendering Issue After Stage Teardown IsaacLab#7472
• Currently, the test with fabrics on is disabled, reflecting the fact that this property is currently not preserved.

[alexmillane]

Self review.

[arena-review-bot]

🤖 Isaac Lab-Arena Review Bot

Summary

Adds a second regression test for the Lab render-after-rebuild bug, checking Fabric omni:fabric:worldMatrix values directly instead of comparing rendered pixels — a genuinely cheaper failure to diagnose, since it names the offending prim paths. The test itself is well built. The concern is the two edits to test_render_after_stage_rebuild.py, which look like debug leftovers rather than intended changes.

Findings

🔴 Critical: isaaclab_arena/tests/test_render_after_stage_rebuild.py:177 — the @pytest.mark.skip is commented out, un-skipping the known-failing GPU+Fabric render test. That contradicts the PR description and the TODO directly above it, and will turn the with_cameras phase red. Restore the marker (or delete the line rather than commenting it out, if the un-skip is intended).

🟡 Warning: isaaclab_arena/tests/test_render_after_stage_rebuild.py:34 — SAVE_IMAGES flipped False → True, while its own comment still describes True as the opt-in. Every CI run now dumps PNGs per camera.

🟡 Warning: isaaclab_arena/tests/test_prims_after_stage_rebuild.py:46 — _build_droid_env (plus HEADLESS/ENABLE_CAMERAS and the reset-and-step loop) is a near-copy of the render test's. Worth pulling into isaaclab_arena/tests/utils/ so the two tests can't drift. The two copies already differ: only the new one forces --device cpu.

🔵 Improvement: isaaclab_arena/tests/test_prims_after_stage_rebuild.py:41 — MIN_PRIMS_COMPARED = 1 is a thin vacuity floor given the four continue paths in the scan. Asserting that both builds compare the same number of prims would be stronger and drop the magic number.

Test Coverage

This PR is the test. Both new tests carry @pytest.mark.with_cameras and no subprocess marker, so they land in Phase 2 — correct for camera-enabled sim work. The inner/outer pattern is followed properly: the pytest-visible functions call run_function_with_persistent_simulation_app, and all sim-dependent imports (omni.usd, usdrt, pxr, isaaclab.*, and the Arena builder modules) are deferred inside the inner functions. Fabric-on variants of both tests are skipped, so what actually runs in CI is the Fabric-off path — reasonable while the Lab bug is open, and the TODOs carry the shared [lab-render-after-rebuild-bug] tag so they can be found together.

Verdict

Minor fixes needed — the un-skipped render test and the SAVE_IMAGES flip should be resolved before merge; the rest is optional cleanup.

[greptile-apps]

Greptile Summary

This PR adds lower-level regression coverage for stale Fabric world matrices after rebuilding a stage and improves render-comparison image naming. It also inadvertently enables the known-failing GPU-and-Fabric render regression.

• Adds a two-build prim-transform test for camera-enabled Fabric-on and Fabric-off configurations.
• Saves render diagnostics with Fabric-specific filenames.
• Removes the skip from the unresolved Fabric-on render regression.

Confidence Score: 4/5

The PR should not merge until the Fabric-on render regression is skipped again or the underlying rebuild defect is fixed.

The newly enabled test is selected by standard GPU camera-test jobs and deliberately exercises the unresolved Fabric path that its own TODO says renders rebuilt geometry incorrectly.

Files Needing Attention: isaaclab_arena/tests/test_render_after_stage_rebuild.py

Important Files Changed

Filename	Overview
isaaclab_arena/tests/test_prims_after_stage_rebuild.py	Adds focused transform-level regression coverage with the currently broken Fabric-on variant explicitly skipped.
isaaclab_arena/tests/test_render_after_stage_rebuild.py	Improves diagnostic filenames but activates a regression test whose adjacent documentation says the exercised GPU-and-Fabric path remains broken.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
  A[Create camera-enabled environment] --> B[Reset and step simulation]
  B --> C[Read USD and Fabric transforms]
  C --> D[Close environment and rebuild stage]
  D --> E[Repeat transform comparison]
  E --> F{Fabric world matrix stale?}
  F -->|Yes| G[Report offending prim paths]
  F -->|No| H[Regression passes]

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_{Reviews (1): Last reviewed commit: "Add regression test notes." | Re-trigger Greptile}