Constant VULKAN_TOSA_FP8_CAPABILITY 

pub const VULKAN_TOSA_FP8_CAPABILITY: CapabilityDescriptor;

The FP8 tier’s admitted boundary (ADR 0009): (FP8, FP8) -> FP16 MATMUL and exact FP8 data movement. Like the FP16 tier it needs no device feature — the widening is crate-owned integer and binary32 code and nothing writes FP8 except a raw byte copy — so it is advertised on every device the backend opens, with numerics identical everywhere.