Track retained layout validity explicitly

core/src/ui/mod.rs

@@ -10,10 +10,12 @@ use crate::{
 pub const CHAIN_LIMIT: u32 = 64;
 
 mod active;
+mod holds;
 mod painter;
 mod render_state;
 
 pub use active::*;
+pub use holds::*;
 pub use painter::{Painter, PrimitiveLike};
 pub use render_state::*;