[hujc7]

Summary

The Newton RTX viewer now honours an explicitly set OVRTX_SHADER_CACHE_PATH. CI restores its OVRTX shader cache into that directory, but Newton's viewer creates its own OVRTX renderer and never used it, so it compiled every shader on each run. Without the variable, OVRTX keeps its default cache location; nothing changes.

The redirect also no longer initializes OVRTX. It only sets the cache path, leaving initialization and its configuration to whichever renderer is created first.

Description

1. Isaac Lab's NewtonViewerRTX subclass overrides _init_ovrtx, where Newton's ViewerRTX creates its renderer on the first frame, and calls redirect_shader_cache() before Newton's implementation. The subclass already overrides Newton's _init_window the same way. No Newton configuration is copied into Isaac Lab.
2. redirect_shader_cache, added in Add OVRTX shader cache for CI rendering tests #6905 for CI cache persistence, took a RendererConfig because reaching the OVRTX settings extension called ovrtx_initialize with it. It now loads the library without initializing, as OVRTX itself does when registering schema paths, and applies the two /rtx/shaderDb paths. OVRTXRenderer calls it without a config, and its one-caller helper apply_shader_cache_settings is folded into it.
3. Tests check the redirect never initializes OVRTX and that the viewer redirects before Newton creates its renderer. The viewer test also fails if Newton renames _init_ovrtx.

Why it was missing

The Newton RTX visualizer (#6658) predates the shader cache (#6905), which added the redirect inside OVRTXRenderer for the rendering-correctness jobs. #8006 later restored the cache in the isaaclab_visualizers job, but Newton's own renderer never read it.

Effect

Where	Before	After
x86 CI, isaaclab_visualizers job (run), cache restored but unused	104 s	not yet measured
x86 desk, cold then warm cache	142 s	49–57 s
ARM CI (#8233 benchmark), warm cache	301 s	27 s

On ARM the cache seeded only by the Cartpole rendering tests fully covered the viewer (0 MB growth), so the cache-warm job needs no change.

This is interim. #8303 plans to adopt Newton #4627 (ViewerRTX(renderer=...)), after which the viewer borrows the renderer Isaac Lab creates and the override can be removed.

Validation

On x86 desk with ovrtx 0.5.1.385782, the develop pin:

1. test_ovrtx_shader_cache_redirect.py and test_ovrtx_renderer_contract.py: 63 passed. test_newton_adapter.py -k newton_rtx: 2 passed; the viewer test fails with the redirect removed.
2. With an empty OVRTX_SHADER_CACHE_PATH, test_visualizer_integration_newton_rtx.py (3 passed, 2 skipped) and the legacy-newton-ovrtx_renderer-static Cartpole kitless case (1 passed) each filled the directory (119 MB).
3. Setting the paths before initialization survives a later ovrtx_initialize. A renderer created after an earlier initialization still applies its own log level and log file.

Type of change

1. Bug fix (non-breaking for users; redirect_shader_cache drops its config parameter and apply_shader_cache_settings is removed).

Checklist

• I have read and understood the contribution guidelines
• I have run the pre-commit checks with uv run isaaclab --format
• I have added changelog fragments for isaaclab_ov and isaaclab_visualizers
• I have added tests that fail without the change
• My name already exists in CONTRIBUTORS.md