fn check_native_toolchain(target: TargetBackend) -> Result<(), String>Expand description
§12 pre-flight: confirm the native toolchain a non-WGSL/native target needs
is present, reusing the same probes as shader doctor. Pure-WGSL/SPIR-V
paths need no native compiler and return Ok(()) immediately. The error is
actionable and points at shader doctor.