Function user_texture_binding_name 

pub fn user_texture_binding_name(slot: usize) -> String

WGSL binding name for user-texture slot slot. The codegen wrapper declares var sampler_user_<n>_texture: texture_2d<f32> for each slot 0..MAX_USER_TEXTURE_SLOTS, and this is what the translator emits in textureSample(...) calls for plan-routed samplers.