re(ui): a static composite is only meaningful for a screen that settles

The model's sharpest prediction, tested with its control. The draw log
says that on the developer splash the _eff glows are drawn on frames
94-115 and the logos on 116-211, so at the moment the reference capture
was taken EVERY glow is already finished -- including the two that have
plateaus and which rest_plateau therefore renders visible. Suppressing
them should help on the splashes and hurt where a screen genuinely
settles.

  publisher splash   +0.9604 -> +0.9982   +0.0377
  developer splash   +0.9659 -> +0.9980   +0.0321
  title    (control) +0.9500 -> +0.9480   -0.0020
  main menu(control) +0.9460 -> +0.8544   -0.0916
  EXTRAS   (control) +0.9440 -> +0.8370   -0.1070

Both splashes jump to about 0.998; all three persistent screens get
worse. The control is what makes this a finding rather than a
coincidence: the same edit helps exactly where the model says it should
and hurts exactly where it says it should not.

So rest_plateau is not over-drawing in general -- it over-draws on
TRANSIENT screens. A plateau mid-animation means the element is held at
that point in the timeline, not that it is on screen once the screen has
settled. Where a screen settles, the held pose IS the settled pose and
the rule is measurably right.

And that answers the question left open several iterations ago -- what
"rest" means for a transient element. It does not mean anything: the
splashes never rest. A static composite of them can match a chosen frame,
and about 0.998 is what these captures' frame is worth, but the format
does not answer a question the screen never poses.

For the port: play the timeline for the two splashes, which the settled
keyframe timing now supports, and composite statically for title, main
menu and EXTRAS.

METHOD: an edit that improves one set of cases is only interesting once
you have shown it damages the cases where it should.

docs/port/HANDOFF.md

@@ -328,6 +328,21 @@ authored version can be deleted.
   ⚠️ Reach: static composites at rest against single frames — this says nothing
   about animation.
 
+* ✅ **A static composite is only meaningful for a screen that SETTLES — the two
+  splashes are animations.** Measured with its control: suppressing the `_eff`
+  glows takes the **publisher splash 0.9604 → 0.9982** and the **developer splash
+  0.9659 → 0.9980**, while the same edit makes the title −0.002, the main menu
+  **−0.092** and `EXTRAS` **−0.107** worse. The draw log says why — on the
+  developer splash the glows draw on frames 94–115 and the logos on 116–211, so
+  at the captured moment every glow is already finished, including the two with
+  plateaus that `rest_plateau` renders visible.
+  So `rest_plateau` is right where a screen settles and over-draws where it does
+  not. **There is no "resting pose" for the splashes** — they play through and
+  leave, and a static composite of them is a picture of one arbitrary frame
+  (≈0.998 for the frame these captures hold). **Play the timeline for the two
+  splashes; composite statically for title / main menu / `EXTRAS`.**
+  [`structures/ui-resting-pose.md`](../re/structures/ui-resting-pose.md)
+
 * **Menu order is geometric.** Buttons sorted top-to-bottom by resting Y. This is
   ✅ correct for a vertical menu and is **not** a decoded neighbour graph — the
   disc's real navigation structure is unknown, and `opt ` is *not* a focus link