docs: backlog — primitives drawn opt-in; their paint order needs a runtime read

docs/re/BACKLOG.md

@@ -102,11 +102,21 @@ See [`structures/ui-composable-bundles.md`](structures/ui-composable-bundles.md)
   too, and the tie-break was grabbing it, which erased the word PAUSE; a run
   ending on the last keyframe is now excluded.
   See [`structures/ui-resting-pose.md`](structures/ui-resting-pose.md).
-* ❔ **Draw the `.prm` quads.** ← *next; nothing is blocking it now.* A solid
-  `fade`-coloured rect at `pivot × 2`, painted in layer-key order like everything
-  else. The title's `pteff00.prm` rests transparent and its `pteff02.prm` at
-  `0x00000000`, so the title should be unchanged — that is the regression check.
-  `GP_*` screens that dim behind a menu are where it should show.
+* 🟡 **The `.prm` quads are drawn, opt-in** (2026-08-19).
+  `ComposeOptions::include_primitives` / `screen render --primitives`. On the
+  title — the one screen with ground truth — it takes mean luminance from **+18 %
+  to −1.3 %** of the capture (76.30 → 63.72 vs 64.58) and mean abs diff 16.07 →
+  13.08. Off by default because of the item below.
+* ❔ **Where a primitive paints. ← next, and it needs the emulator.** A primitive
+  has no `T8aD` header, so no layer key, and the derived order forces the keyless
+  last — which wipes **36 of the 125** builds that draw one (`GP_DIALOG`'s
+  `pzeff00.prm` is a single opaque-black full-screen keyframe). No constant
+  default works: the splash paints its primitive **first** (a black backdrop),
+  the title paints one at slot **4** and another **last**, and declaration order
+  fails the title too. Cheapest first step: a third measured paint order from a
+  screen carrying exactly one primitive — the `GP_DIALOG` DIFFICULTY box, which
+  is reachable from the main menu, would say whether its dim is first or last.
+  This is a runtime child-list read, so it is an emulator item, not a static one.
 * ❔ **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