Function gpu_mip_count 

pub fn gpu_mip_count(vsid: u32) -> u32

GPU.11 — how many mip levels a chunk of side vsid actually yields under GPU_MAX_MIPS. Mirrors the stopping rule in Vxl::generate_mips (src_vsid > 1 && src_z > 1 && n < max) so the upload, the per-slot stride math in crate::scene, and the shader all agree on the level count for a given vsid. Always >= 1 (mip-0).