iris: drive animation from painter frame time

docs/PLAN.md

@@ -813,6 +813,14 @@ widget changed. Winit's user-event proxy and Android's posted callback are
 private implementations of that wake; applications do not define platform
 event types or manually request redraws.
 
+Frame-driven visuals use that same draw path rather than a parallel animation
+registry. The host supplies the presentation timestamp to `Painter`; a widget
+reads it during `draw` and calls `request_next_frame` while it remains active.
+Iris stages the requesting widget's invalidation until the current retained
+redraw has finished, then the host schedules the next platform frame before
+renderer update or swapchain acquisition. `Widget::draw` still returns unit,
+and `Widget` has no tick callback.
+
 **Iris ships no fonts, and font families are application-named strings**
 (2026-09-12). Applications register their own font bytes on `Ui` and select
 them by the same string used by text widgets. The public boundaries accept