Function default_layer_registry_with 

pub fn default_layer_registry_with(options: LayerOptions) -> LayerRegistry

Variant of default_layer_registry that also honours per-server LayerOptions (currently: the LongHold threshold). Called by mse serve with the resolved config value; every other caller (tests, in-tree bins that don’t tune the LongHold knob) can keep using the zero-arg default_layer_registry.