port: refute the peer's tone/geometry positive control, and label the number that misled it

docs/re/structures/title-residual-tone-vs-geometry.md validates its per-level-LUT
instrument with a positive control on the main menu, on the grounds that "the port
measures only 0.06 % of pixels differing, so geometry is essentially right".

That 0.06 % is verify-capture's, and it counts pixels differing by more than ~64
levels -- a gross-displacement detector. It is blind to sub-pixel offsets and
antialiasing differences, which are exactly what a per-level LUT also cannot close.

Measured: after the LUT, the menu's remaining residual is 6.94 on edge pixels and
2.20 on flat ones, 3.2x. Known negative -- render vs itself under a pure gamma --
leaves 0.00, exactly, because a per-level LUT inverts a per-level effect perfectly.
So the concentration is spatial and the menu is not a geometry-free control.

Their conclusion survives: the title's 32 % never depended on the control. The
refutation is of the validation only, and I say so.

The half that is mine: verify-capture's header now states what the diff column
thresholds and what it therefore cannot establish, next to the number itself.

Not settled: whether the menu's spatial error is misregistration, antialiasing, or
a misplaced soft element. This does not separate them.

tools/port/verify-capture

@@ -9,6 +9,23 @@
 # this file did not exist. The port has had a harness comparing two renderers
 # that share its assumptions, and none comparing it to the game.
 #
+# 🔴 WHAT THE `diff` COLUMN DOES NOT SAY. It counts pixels surviving
+# `-threshold 25%` -- differing by more than ~64 levels. That is deliberate: it
+# detects a missing or MISPLACED element, which is a large connected blob. It is
+# blind to sub-threshold spatial error -- a one-pixel offset, a soft edge in a
+# slightly wrong place, an antialiasing difference -- because none of that moves
+# a pixel 64 levels.
+#
+# So `main_menu 0.06%` means NO GROSS DISPLACEMENT. It does NOT mean the
+# geometry is right, and it has already been read that way by another agent:
+# `docs/re/structures/title-residual-tone-vs-geometry.md` uses this screen as a
+# tone-only positive control, citing this number as "geometry is essentially
+# right". Measured 2026-08-31 against that capture: after fitting a per-level LUT
+# -- the most general tone model there is -- the remaining residual is 6.94 on
+# edge pixels against 2.20 on flat ones, a 3.2x concentration. A purely tonal
+# residual leaves a per-level LUT exactly 0.00 (checked, by construction). The
+# menu carries spatial error this column cannot see.
+#
 # ⚠️ That gap is not academic. `docs/re/captures/ORACLE-CAPTURES.md`: two
 # renderers agreeing proves nothing, and this corpus has been bitten three times
 # -- the dropped `pteff05` background, the scale-0 rect, and `rest()`. Every one