re(ui): settle 8AX vs ptbase statically -- the game draws the full-res one

I had parked this as "needs a per-draw capture recording texture base
addresses". It did not. 8AX (1280x720) and ptbase (640x360 at 200%) are
the SAME artwork at two resolutions, which is exactly why comparing
either against a capture is inconclusive -- and why comparing their
DIFFERENCE is not. Compute 8AX - upscale(ptbase), the detail only 8AX
has, and ask whether the capture contains it.

Both candidates are first mapped into the capture's tone domain with the
measured gamma; without that the residual is dominated by the tone
difference and the test is blind.

  main menu  corr +0.0475   controls +0.0032 shift, -0.0075 flip   68% of ceiling
  title      corr +0.0634   controls +0.0095 shift, +0.0086 flip   68% of ceiling

Two independent screens, both at 68% of the theoretical ceiling
(sd of the 8AX-only detail over sd of the capture residual), 7-15x their
matched controls. The controls preserve spatial correlation and destroy
only alignment, so they are what "no signal" looks like.

So the recommendation changes: resolve the name and draw 8AX at 1:1.
Upscaling ptbase 2x is wrong, not merely softer. Still do not draw both --
an opaque layer over an identical one costs fill and hides later changes,
and ptbase's element is the one carrying the keyframes, so a consumer
needs its timing with 8AX's pixels.

Also recorded and withdrawn: a cruder pixel-pair test gave 0.00-0.72 for
upscales, 0.98 native and 1.01 for the capture -- apparently decisive.
Additive noise raises both terms of that ratio equally and drives any
value toward 1; fitting a noise term, both "native + noise" and "bilinear
+ noise" reproduce the observed numbers. The conclusion is right, that
test does not establish it, and it is in REFUTED because the number looks
conclusive and is not.

Not shown: whether ptbase is also drawn underneath. 8AX is ~86% opaque
and carries the same art, so it would hide it either way.

docs/re/REFUTED.md

@@ -469,3 +469,16 @@ neighbourhood, not just the line.
   already retracted it and located three cues in `Static.slb` that decode to PCM.
   The retraction never reached the row the port agent reads. Handoff row fixed;
   `tools/re-capture/handoff_lint.py` now checks for this class.
+* "which of `8AX` and `ptbase` the game draws needs a per-draw capture recording
+  texture base addresses" → **mine, and refuted — it is settled statically.** The
+  two carry the same art at two resolutions, so neither compares usefully against
+  a capture; their *difference* does. Correlating the capture's
+  departure-from-upscale against the 8AX-only detail gives +0.0475 (main menu)
+  and +0.0634 (title), both 68 % of ceiling against matched controls of ≤0.0095.
+  The game draws the full-res `8AX`.
+  [`ui-8ax-fullres-background.md`](structures/ui-8ax-fullres-background.md)
+* "the pixel-pair ratio shows the capture is native, not an upscale" → **mine,
+  and withdrawn as evidence.** Upscales give 0.00–0.72, native 0.98, capture 1.01
+  — but additive noise pushes any such ratio toward 1, and both "native + noise"
+  and "bilinear upscale + noise" fit the observed values. The conclusion happens
+  to be right; this test does not establish it.