pub fn require_gpu_preflight() -> Result<(), String>Expand description
Require-GPU preflight, independent of backend routing.
When the policy is not GpuRuntimePolicy::Required this is a no-op and
returns Ok(()). When it is required, the contract is to refuse to run when
no usable GPU adapter is detected. This check fires on the no-GPU path the
flag exists for; it does not depend on select_backend having chosen GPU
first.
Returns Err(diagnostic) when no acquired CUDA or WGPU peer passes the
production region-presence parity self-test. The caller maps that to the
documented exit code 12. Returning an Err here - rather than calling
std::process::exit from the library - keeps embedders alive (finding
M12).