fix(theme): destructive buttons were invisible after #98 (1.03:1)

e9dd3d1 pinned dialog button labels to base00 for dark palettes. That is
correct for suggested-action, whose background adw-gtk3 builds opaquely as
mix(white,@accent_bg_color,0.9) — but destructive-action is the one class
whose background is derived from currentColor:

  background-color: mix(@destructive_color, alpha(currentColor, 0.15), 0.9)

so pinning the label dragged the background down with it. On Boreal the
"Delete" button of a GtkMessageDialog rendered #21272F on #252931 —
1.03:1, invisible — and light palettes hit the same 1.03:1. The most
safety-critical button in a confirmation dialog was the one that vanished.

Pin the destructive background to the same opaque pastel ladder
suggested-action uses. Enabled-only (:not(.flat):not(:disabled)): the
sheet's disabled chrome already renders legibly and must keep it.

Boreal 1.03 -> 6.19:1, summer-day 1.03 -> 2.74:1 (= upstream's
white-on-accent convention; the residual light-mode weakness is #130).

V2: GtkMessageDialog rendered under the real HM session and viewed —
boreal before/after, summer-night (whole-swap), summer-day (light).
Scripted checks stayed green throughout and never saw this; only the
render did. Follow-ups #129 (permanent guard) and #130 filed.

agent/BACKLOG.md

@@ -73,6 +73,29 @@ DPMS-while-docked) deferred to the LATER revisit.
 
 ## NEXT
 
+### 129. Permanent guard for the GTK button-colour trap (#98 follow-up)
+
+The #98 regression (destructive-action at 1.03:1, invisible) was caught only
+by rendering a dialog — every scripted check was green, because the bug lives
+in adw-gtk3's `mix(@destructive_color, alpha(currentColor,…))` background, not
+in our CSS. `tools/theme-shot.nix` is deliberately not a CI gate (full-desktop
+VM), so add the cheap static half: assert that for every theme, any rule that
+pins a button label colour also pins that button's `background-color` — i.e.
+no pinned label may sit on a `currentColor`-derived background. Guards the
+class, not the instance. The scratch render harness that found it is worth
+promoting to `tools/dialog-shot.nix` as a maintainer tool alongside theme-shot.
+
+### 130. GTK accent buttons sit at ~2.7:1 in light themes
+
+Fallout noted while fixing #98: in light palettes the suggested/destructive
+labels are base00 (cream) on saturated accent/bad — summer-day measures
+**2.72:1** (suggested) and **2.74:1** (destructive), under AA 4.5 and even
+under the 3:1 large-text floor. Not a regression: upstream adw-gtk3 does the
+same (`color: white` on the accent), so we currently match GNOME. Decide
+whether Nomarchy holds itself higher — darker label, or a darker accent mix
+for light palettes — and note `tools/check-theme-contrast.py` covers palette
+pairings only, never GTK widget surfaces. `[human]` for the aesthetic call.
+
 ### 120. A netinstall ISO, next to the fat offline one
 
 Bernardo 2026-07-14, after seeing the measured size: **keep the current ISO