re(ui): refute my own fix for rest(), and correct the defect rate by 65%

Two corrections from one experiment.

A keyframe group is entry -> hold -> exit, and the exit ends invisible:
on the five port screens the final keyframe is invisible for 21/24
(title), 8/16 (main menu), 12/18 (EXTRAS), 2/3 and 6/7 (splashes). So the
screen as seen is the HOLD, which is why rest_plateau is the right
primary rule and why "rest = last keyframe" would empty every screen.

That suggested a fix: an element with no hold has no representative pose,
so draw nothing rather than guess an endpoint. Tested through compose's
visible mask and correlated against the live captures:

  title       +0.9500 -> +0.6839   -0.2661
  main menu   +0.9460 -> +0.9037   -0.0423
  EXTRAS      +0.9440 -> +0.9094   -0.0346

Refuted on all three, and the reason invalidates a number I published. An
element with a SINGLE keyframe has no adjacent pair, so the plateau test
marks it plateau-less -- but its one pose is unambiguously its rest.
Suppressing those removes backgrounds and full-screen layers, which is
the title's -0.27.

  no plateau (as published)      3 807  (24.57 %)
    ... single-keyframe          1 502  trivially at rest, not a guess
    genuinely ambiguous          2 305  (14.88 %)

So rest() guesses for 2 305 elements, not 3 807 -- the figure I gave the
port overstated the defect by 65%. Corrected in HANDOFF and the page.

METHOD: a predicate over adjacent PAIRS silently misclassifies a
one-element list; and acting on a claim is a better test of it than
re-reading it -- this flaw survived a census, a write-up and a handoff
row, and died the moment the rule was used to change a rendering.

docs/re/structures/ui-resting-pose.md

@@ -332,7 +332,9 @@ them before it counts anything. Output: [`data/plateau-census.txt`](../data/plat
 | | |
 |---|---|
 | elements with a keyframe group, disc-wide | **15 493** |
-| no plateau → **rest pose is guessed** | **3 807 (24.57 %)** |
+| no plateau | 3 807 (24.57 %) — ⚠️ **overstated, see the correction below** |
+| …of those, **single-keyframe** (trivially at rest, not a guess) | **1 502** |
+| **genuinely ambiguous** (2+ keyframes, no plateau) | **2 305 (14.88 %)** |
 | of those, current rule returns an **invisible** pose | 1 711 (44.9 %) |
 | of those, current rule returns a **zero-scale** pose | **195 (5.1 %)** |
 | the two candidate rules **agree** | 1 911 (50.2 %) |
@@ -378,9 +380,54 @@ siblings'. It sits above.
 
 ### 🟡 Where this leaves it
 
-The **defect** is established and measured: `rest()` guesses for 24.57 % of
+The **defect** is established and measured: `rest()` guesses for **14.88 %** of
 elements disc-wide and returns a degenerate zero-scale pose for 195 of them.
 The **fix** is not decided — "last keyframe" is refuted, and the current rule
 survives on the only captured element that discriminates. ⚠️ For the menu port
 specifically this is **not a blocker**: one element on one screen, and our
 current answer for it is the defensible one.
+
+
+---
+
+## 🔴 The 24.57 % was overstated, and my proposed fix is refuted
+
+**2026-08-29.** Two corrections, both from one experiment.
+
+### The prediction: draw nothing for an element with no held pose
+
+A keyframe group is **entry → hold → exit**, and the exit ends invisible — on the
+five port screens the final keyframe is invisible for **21/24** (title),
+**8/16** (main menu), **12/18** (`EXTRAS`), **2/3** and **6/7** (splashes). So
+the screen "as seen" is the *hold*, which is why `rest_plateau` is the right
+primary rule and why "rest = the last keyframe" would empty every screen.
+
+That suggested a fix: an element with **no** hold has no representative pose, so
+draw nothing rather than guess an endpoint. Tested via `compose`'s `visible` mask
+(`examples/plateauless_suppression.rs`), correlated against the live captures:
+
+| screen | as-is | plateau-less suppressed | Δ |
+|---|---|---|---|
+| title | +0.9500 | +0.6839 | **−0.2661** |
+| main menu | +0.9460 | +0.9037 | −0.0423 |
+| `EXTRAS` | +0.9440 | +0.9094 | −0.0346 |
+
+**Refuted, decisively, on all three.**
+
+### Why — and it invalidates the headline number
+
+An element with a **single keyframe** has no *adjacent pair*, so the plateau test
+marks it plateau-less. But a single-keyframe element is not animated at all: its
+one pose *is* its rest, unambiguously. Suppressing those removes backgrounds and
+full-screen layers, which is where the title's −0.27 comes from.
+
+The same flaw is in the census this page published:
+
+| | |
+|---|---|
+| no plateau (as published) | 3 807 (24.57 %) |
+| …of which **single-keyframe** | **1 502** — trivially at rest |
+| **genuinely ambiguous** | **2 305 (14.88 %)** |
+
+So the guessed-rest population is **2 305, not 3 807** — the published figure
+overstated it by **65 %**. The defect is real and smaller than reported.