Module render 

External-piece registration surface (DESIGN.md §8.2). The renderer! macro registers a piece’s per-toolkit native renderer into a backend’s RENDERERS slice with typed make/update (the macro inserts the &dyn Any downcast) and no hand-written linkme boilerplate. fill_measure is the shared “growing leaf” sizing, so pieces stop hand-rolling it per backend.

Functions

fill_measure

A leaf measure that FILLS the space it’s proposed — for growing leaves (a web view, a canvas, a Lottie view). Use as measure: day_pieces::fill_measure in renderer!. This gives one uniform “fill” answer across every backend (some backends’ measure: None default returns a view’s natural size, which collapses a size-less native view).