Function validate_step_fp8_checkpoint 

pub fn validate_step_fp8_checkpoint(
    src: &dyn TensorSource,
    contract: &ModelParallelContract,
) -> Result<usize, TopologyError>

Prove that the official Step checkpoint exposes every routed expert projection as a native stacked block-128 E4M3 bank. Converted and per-tensor artifacts do not inherit this contract.