Runtime contrast for hand-written hex backgrounds

DESIGN/10's ≥ 4.5:1 rule gets its owner. ContrastMath is the pure seam:
WCAG relative luminance (piecewise sRGB linearization), symmetric
contrast ratio, source-over compositing (an #RRGGBBAA board colour
resolves over the window background of the active appearance), and
inkChoice — native label if it clears AA, else the other appearance's,
else the higher ratio with meetsAA false (a mid-grey hex can max out
below 4.5 against both 85%-alpha labels; the app paints the best
available rather than overriding the user's colour). BoardTextInk is
the board's application: the decision is a ColorScheme, not a Color —
the text on the board fill is a hierarchy (.primary/.secondary/
.quaternary), and overriding the subtree's scheme moves the whole
vocabulary coherently. Recomputed on appearance change by construction
(read in body); label/backdrop colours resolve inside the asked-for
appearance, Increase Contrast variants included.

Two render sites — the only board text that sits on the user's colour:
the lane header (lanes draw no plate; title, icon, badge, rename field
and the + button land directly on the board fill) and the trash header
(its wash is ~5% effective alpha). Menus, popovers, and drag replicas
deliberately stay native; card faces carry their own opaque plates.

The card's premise fell during implementation: 03's "palette pairs
AA-verified at design time, pinned by a computed-contrast unit test"
was false — no such test existed, and the m4 path drew the native label,
failing AA in one appearance for all twelve wells (obsidian in Light
Mode: 1.0:1). Palette names now route through the same ink selection
(paintedColor delegates to Palette.nsColor — one predicate with
BoardView's paint decision), and PaletteContrastTests pins that the
chosen ink clears AA for every well in both appearances — plus
theNativeLabelIsNeverEnough, which would have failed on the m4 code.
Filed on the Redesign board for ratification. 1579 unit tests green,
both schemes build.

Claude-Session: https://claude.ai/code/session_01SR4XGjmBE16ZUYWpfFHXwY

Kanban/UI/Board/TrashLaneView.swift

@@ -96,6 +96,10 @@ struct TrashLaneView: View {
     /// Styling), which is exactly the case the setting exists for (`Accommodations.Wash`).
     @Environment(\.accessibilityReduceTransparency) private var reduceTransparency
 
+    /// The window's appearance — 10-accessibility.md's runtime-contrast input, read in `body` so a
+    /// light/dark flip recomputes the header's ink (`LaneView.colorScheme`'s twin, for its reason).
+    @Environment(\.colorScheme) private var colorScheme
+
     /// The live body metric — this column's geometry is `LaneView`'s, derived from the same font
     /// (`BoardMetrics`), because these are the same cards in a column that must read as their
     /// sibling.
@@ -226,6 +230,25 @@ struct TrashLaneView: View {
                         ))
                 }
         }
+        // **The board's computed contrast ink** (10-accessibility.md; `BoardTextInk`) — the trash
+        // header is the second and last place on the board where text sits on the user's colour,
+        // whether that colour came from the palette grid or from a hand-written hex.
+        //
+        // The wash between the text and the board background does not save it: `.quaternary` at 50%
+        // is a ~5%-alpha tint (`Accommodations.trashHeaderWash`), so the glyphs are effectively on
+        // the board colour, and the decision is deliberately taken against that colour rather than
+        // against a three-layer composite — modelling a tint that shifts the surface by a couple of
+        // luminance points would add a whole layer of arithmetic to move no decision.
+        //
+        // **Outside the `.background`, unlike the lane's**, so the wash and the hatch flip with the
+        // text: both are drawn in `.quaternary` — the same label vocabulary — and a hatch left in the
+        // window's appearance over an inverted board is a dark texture on a dark surface, which
+        // would quietly cost the trash the *non-colour* distinction 10-accessibility.md's
+        // "state is never colour-alone" requires of it.
+        .boardTextInk(BoardTextInk.scheme(
+            forBoardBackground: store.snapshot.background,
+            appearance: colorScheme
+        ))
         // The container carries the label and the count (see `body`), so the header itself is
         // decoration for VoiceOver rather than a second element saying the same thing.
         .accessibilityHidden(true)