Fix frame pacing

docs/how-it-works.md

@@ -76,6 +76,8 @@ Built-in presentations include push, reveal, adjacent-page slide, fade, modal, s
 
 The runtime publishes progress as a CSS custom property. Built-in motion is mostly expressed through transforms and opacity, keeping per-frame JavaScript work constant. Applications can register presentations whose layer styles are functions of progress, role, direction, and optional source geometry.
 
+First use has unavoidable setup work—downloading/evaluating a lazy chunk and mounting/layout of its Vue tree—but it does not need to compete with the transition. The runtime completes lazy resolution first, then gives newly mounted destinations a browser preparation frame before advancing progress. Full-surface dimming uses a composited opacity overlay rather than a changing CSS filter so WebKit does not repeatedly rasterize the route subtree.
+
 ## Gesture ownership
 
 Gesture recognition uses Pointer Events and waits for clear directional intent before claiming a pointer. Vertical scrolling remains available through `touch-action`, while form controls, editable content, and elements marked with `data-native-gesture="ignore"` are excluded.