Function gpu_arm_compiled 

pub const fn gpu_arm_compiled() -> bool

Whether the GPU rasterization arm is compiled into this build of facett-core (i.e. the wgpu feature is on). The single source of truth for “can decide ever return Backend::GpuVello”. Re-pointed skins/engines (e.g. facett-graphview) should key their expectations off THIS, not their own crate’s feature flag — workspace feature-unification can light up facett-core/wgpu independently of a downstream crate’s own gpu feature.