Fix MaterialX shader generation when building the complete OpenMoonRay source tree.

[nicolaspopravka]

Compatibility:

patch

Issues/Tickets:

Release notes comment:

Fix MaterialX shader generation when building the complete OpenMoonRay source tree.

Comments for the reviewer:

materialx_shaders checks for the scene_rdl2 directory in the OpenMoonRay build tree during CMake configuration. openmoonray currently adds materialx_shaders first, so that directory does not exist yet and the shader generator does not receive the scene_rdl2 Python path.

Configure scene_rdl2 before materialx_shaders so the existing path and CMake logic is used.

This is exposed by a clean build with BUILD_MATERIALX_SHADERS=ON and no previously installed scene_rdl2 Python module. Builds where the option is disabled or scene_rdl2 is already available through PYTHONPATH do not encounter it.

I tested this with OpenMoonRay v2026.29.1 and BUILD_MATERIALX_SHADERS=ON. The full build completed, generated and installed materialx_shaders/shaders.py, and installed the shader JSON files. MoonRay, hd_render, and usdrecord render checks passed

Look or scene setup change:

Special notes for production:

Attention/Reviewers:

AI Assisted Development:

Assisted-by: OpenAI Codex / GPT-5

I used Codex to investigate and implement the initial change and prepare the validation. I reviewed the patch and test results and take responsibility for the contribution.

Checklist:

• Documentation has been updated.
• Includes new unit tests.
• Includes new RATS tests.