docs: backlog — tie-break refuted six ways; residual is one blend on one screen

docs/re/BACKLOG.md

@@ -123,11 +123,25 @@ See [`structures/ui-composable-bundles.md`](structures/ui-composable-bundles.md)
   `include_primitives` stays off by default. A capture of any screen carrying one
   would close it.
   See [`structures/ui-prm-primitives.md`](structures/ui-prm-primitives.md).
-* ❔ **The tie-break.** Elements sharing a layer key are painted in an order
-  nothing predicts — the title's `0x8083` ×5 group paints `14,15,18,16,17` and
-  the `0x80a0` ×7 group paints `0,2,4,7,1,3,5`. Now the *only* thing between the
-  derived order and the measured ones, so it is the next cheap static probe:
-  three measured screens' tied groups against every remaining field.
+* 🟡 **The tie-break — refuted six ways, and its cost measured** (2026-08-19).
+  Elements sharing a layer key: on the **menu and splash** every tied group comes
+  out in declaration order, which the stable sort already gives. The **title** is
+  the only screen that discriminates and nothing predicts it (`0x8083` ×5 paints
+  `eff1, eff2, eff5, eff3, eff4`). Refuted: declaration order, RATC child order,
+  first keyframe time, resting time, resting X/Y, and `T8aD` header words `+00`
+  `+04` `+0c` `+10`. RATC child order is a *strict improvement* (7 misplaced
+  positions instead of 9, and it recovers the logo grouping) and is exact on the
+  other two screens — **not adopted**, because on the one screen that can tell
+  them apart it is still wrong.
+  **What it costs, exactly:** of 3 disagreeing pairs of drawn elements across all
+  three screens, 2 share opaque pixels — `ptlogo_back2eff5` vs `eff3` (22 568 px)
+  and vs `eff4` (32 395 px). The residual is one element's blend on one screen,
+  and it is pinned by a test. The third pair (`ptlogo2` vs `ptlogo_tm`) overlaps
+  by bounding box but shares no opaque pixel; a box test called it a defect and
+  the alpha says otherwise.
+  **Next:** it is one element on one screen, so the cheap move is a fourth
+  measured screen with a tied group — not more static guessing at fields that
+  have all now been checked.
 * ❔ **Blend mode.** Everything is straight alpha-over. The near-white flash
   quads (`0xf0ffffff`) and coloured ones (`0x60ff0000`) may be additive. The
   title capture cannot separate the two — its resting elements are all