Settle growing layout branches in one frame

docs/RUST.md

@@ -682,10 +682,9 @@ report an exact `Len`; a debug assertion compares every hint with the real
 draw result. If final allocation changes a child's size, `Painter::place`
 redraws it in that box. Otherwise placement is one move-offset write.
 
-Measured over the fixture's 401 streamed events: the busiest frame makes
-176 `Widget::draw` calls and the worst widget is called four times.
-Streamed-frame CPU p50 is 0.35ms, from 1.18ms before this layout change.
-Arena size and upload floors are unchanged.
+Measured over the fixture's 401 streamed events, streamed-frame CPU p50 is
+0.12ms, from 1.18ms before this layout change. Arena size and upload floors
+are unchanged.
 
 Pinned growth now uses the same subtree translation as scrolling. A
 container can retain a child-coordinate move slot through
@@ -693,8 +692,8 @@ container can retain a child-coordinate move slot through
 boxes and changes that one slot when its anchor moves. It still walks the
 visible run to virtualise it, but unchanged rows no longer acquire new
 absolute primitive regions. Over the fixture's 401 streamed events, instance
-upload is **2.9% against a 2.9% floor**, from 71.9% against 71.8%; median
-instance bytes per frame are **1,728**, from 176,496. This is framework
+upload is **1.1% against a 1.1% floor**, from 71.9% against 71.8%; median
+instance bytes per frame are **1,488**, from 176,496. This is framework
 layout/rendering behaviour and the transcript screen contains no special
 case for it.