//! A GPU model's agent lanes, passed to the UI to draw in place.
//!
//! Unlike a grid, agents have nothing to rasterise first. Their lanes need `VERTEX` usage, and the colour lane holds
//! packed RGBA, since no upload step widens a palette index.
/// One side of a model's ping-ponged agent lanes.
///
/// A snapshot holds it in an `Arc`, so an in-flight paint callback keeps the buffers alive if the sim thread
/// is torn down mid-frame.