Backend policy
==============

``RhiBackendPolicy`` selects one live backend for a composed viewport set:

::

   Workbench -> QRhi -> D3D11 | Vulkan | Metal

The runtime backend is independent of the generated-code viewer. Windows D3D11 and
Vulkan have draw-recording smoke coverage. Linux/macOS wheel import validates package
construction, not equivalent runtime rendering.

Implementation
--------------

Relevant source: ``rendering/RhiBackendPolicy.*`` and ``app/main.cpp``.