The grid's preferred size was the theme's fluid constant (264 px at the reference surface) capped by the width the parent allocates, so a caller could only shrink it: a lock screen that wants the grid to span most of a phone's width had no way to ask for it, and a container's max_width did nothing past the default. PatternGrid gains a size field with a size( impl Into<Length> ) builder; preferred_size resolves it through Canvas::resolve_geom like the other geometry overrides and still caps it at max_width, and map_msg carries it across. Without the builder the fluid default applies as before. docs/widgets.md describes the builder next to hide_stroke and error; CHANGELOG lists it under Unreleased.