Function config_declared_variant 

pub fn config_declared_variant(config: &ModelConfig) -> Option<Nvfp4Variant>

2026-09-25: Step (1) of detect_nvfp4_variant: the variant the config declares, answered without a WeightStore, so the pre-load residency prediction (qwen35_dense::predicted_residency) asks the same question as the loader. None means the config does not say; the sniffing half of detect_nvfp4_variant then decides.