palette: enlarge the region title into WCAG large class; repoint the grabbed envelope handle off hue

Corrects theme.h's large-text thresholds, names accent/secondary's real
binding limiter, and adds compositeOver so the loop-span fill's 2.25:1
under-floor pair is asserted rather than assumed.

src/core/ui/CLAUDE.md

@@ -43,15 +43,28 @@ L7 sub-pass, 2026-07-27):
   fills on `bg/cell` have a shrunken contrast cushion (primary ~7.6:1, tertiary
   ~5.5:1, secondary only ~3.9:1 since it was darkened — all still clear 3:1, but
   re-check every one on any hue nudge). Body text on an accent fill is a tight AA
-  4.5:1 pair, and for `accent/secondary` it is the *binding* limiter (~4.9:1), not
-  the indicator floor. Take the most pastel value that still clears the floor,
-  approached from the soft side, never re-saturated toward neon "to be safe."
-- **A mark drawn OVER an accent fill answers to two neighbours at once.**
-  `overlay/trace` (the envelope trace on the waveform) must clear 3:1 against both
-  `accent/primary` and `bg/base`, which sit 9.41:1 apart — so `sqrt(9.41)` ≈ 3.07:1
-  is the ceiling for *any* single value, and the role sits at that optimum with no
-  headroom either way. It is therefore confined to the waveform band: no value can
-  clear 3:1 on `bg/cell` and against the lime simultaneously.
+  4.5:1 pair (4.91:1 for `accent/secondary`). **The *binding* limiter on how dark
+  `accent/secondary` may go is neither of those: it is the velocity-curve trace on
+  a HOVER-lightened `bg/cell` at 3.03:1 against a 3:1 floor** — 1.2% headroom, the
+  tightest pair in the tree, and invisible to any rest-surface check. Take the most
+  pastel value that still clears the floor, approached from the soft side, never
+  re-saturated toward neon "to be safe."
+- **A state surface is a DIFFERENT surface.** Hover lightens toward `accent/hot`,
+  pressed darkens, disabled desaturates — each changes the contrast of everything
+  drawn on it. Enumerate the state surfaces a role is drawn over, not just the rest
+  ones; the limiter above is exactly the pair that enumeration missed.
+- **A mark drawn OVER an accent fill answers to two neighbours at once.** THE home
+  for this rule. `overlay/trace` (the envelope trace on the waveform) must clear 3:1
+  against both `accent/primary` and `bg/base`, which sit 9.41:1 apart — so
+  `sqrt(9.41)` ≈ 3.07:1 is the ceiling for *any* single value, and the role sits at
+  that optimum with no headroom either way. Three consequences, all load-bearing:
+  the role is confined to the waveform band (no value clears 3:1 on `bg/cell` and
+  against the lime at once); inside the 20%-alpha loop-span fill it is under floor
+  at 2.25:1, and against `line/hairline`'s zero line at 1.92:1 — both KNOWN,
+  ACCEPTED, and asserted as such, because no trace value fixes either; and any two
+  values that BOTH clear the ceiling sit within 1.05:1 of each other, so a state of
+  this mark (grabbed, hot, selected) **cannot** be carried by color and must be
+  carried by size, fill-vs-outline, or shape.
 - **"Speed is the selling point" — a design constraint on this geometry, not
   just the draw layer.** Sub-frame hover/press/drag feedback must repaint
   immediately on the input message. **No decorative animation** — no
@@ -79,7 +92,7 @@ L7 sub-pass, 2026-07-27):
 - `tab_strip` — REAPER-free scrollable tab-strip layout + hit-test for the named-banks strip.
 - `prune_button` — pure layout/hit-test for the `bank_panel` footer Prune button.
 - `drag_out` — pure OS drag-out module: gesture-boundary decision and path-list assembly. The `InstrumentDrop` gesture signals that the shell should execute an instrument-drop rather than a file-copy drag.
-- `theme` — pure palette module: role→color mapping, REAPER-grey neutral ladder + the pastel accent system, the keyboard strip's spectral ramp (its own three stops, deliberately not aliases of the accents), WCAG contrast-floor helpers.
+- `theme` — pure palette module: role→color mapping, REAPER-grey neutral ladder + the pastel accent system, the keyboard strip's spectral ramp, WCAG contrast-floor helpers + `compositeOver` (the effective color of a translucent fill, so alpha overlays are testable). Only the ramp's MID stop is its own constant; lo/hi are still aliases of `accent/primary`/`accent/tertiary`, so a categorical accent move CAN still reorder the ramp — `testSpectralRampLuminanceIsMonotonic` is the build-time catch, not the structure.
 - `component_geometry` — pure button/slider/list-row geometry + hover hit-test helpers.
 - `action_bar` — pure task-grouped action-bar layout/hit-test: clusters (Capture / Placement / Maintenance / Tagging / Switching).
 - `footer_bar` — pure footer layout/hit-test: `[Arrange|Design]` mode-toggle geometry, Tail button, and Prune placement.
@@ -93,7 +106,15 @@ L7 sub-pass, 2026-07-27):
 
 - The WCAG contrast-floor pairs above are real math in `theme`'s tests, not a
   visual eyeball check — any new hue or role needs its own contrast-floor
-  assertion.
+  assertion. Enumerate the draw sites by grep, not from memory: the enumeration
+  must cover state surfaces (hover/pressed/active), translucent composites, and
+  anything else drawn into the same rect, not just the rest surfaces.
+- **A text color's floor is set by its FONT, not by its role.** WCAG's large-scale
+  class needs ≥24px, or ≥18.66px BOLD (`theme.h`'s thresholds); anything smaller is
+  body class and answers to 4.5:1. A draw site relying on the 3:1 floor must pin its
+  font metrics against those constants — `draw_kit.cpp`'s `Font::RegionTitle` is the
+  worked example. A prior revision wrote the threshold ~25% low and let 15px
+  semibold clear a floor it was not entitled to.
 - `card_drag`'s precedence order must stay a pure decision helper mirroring
   `drag_out::decideGesture` — don't let a shell reimplement gesture precedence
   ad hoc; the cursor-cue mapping in the shell must stay a thin lookup over the

src/core/ui/theme.cpp

@@ -34,22 +34,20 @@ constexpr KitColor kDirHairline   {74, 74, 74, 255};   // #4a4a4a — subtle ste
 constexpr KitColor kDirTextPrimary{220, 220, 220, 255};  // #dcdcdc
 constexpr KitColor kDirTextDim    {168, 168, 168, 255};  // #a8a8a8 (lifted from #a0a0a0)
 
-// Accent system: primary = pastel lime (the live/active/selected signal); secondary = deep
-// teal, tertiary = pastel purple (CATEGORICAL distinctions — a KIND, never intensity).
-// accent/hot is a brighter tint OF the primary for hover/live/drag. Secondary is the one
-// accent off the pastel side: its binding limiter is the AA 4.5:1 text-on-fill pair (a bg/base
-// label on a secondary fill), NOT the 3:1 indicator floor, so it cannot go darker than this.
-// warn is reserved for byte-deleting states only.
+// Accent system — roles and their categorical meaning are core/ui/CLAUDE.md's. Warning only:
+// secondary CANNOT go darker. Its tightest pair is the velocity-curve trace on a HOVER-lightened
+// bg/cell (3.03:1 against a 3:1 floor — the whole tree's thinnest margin), which no rest-surface
+// check sees.
 constexpr KitColor kDirAccentPrimary  {176, 224, 152, 255};  // #B0E098 — pastel lime
 constexpr KitColor kDirAccentSecondary{56, 168, 160, 255};   // #38A8A0 — deep teal
 constexpr KitColor kDirAccentTertiary {194, 170, 232, 255};  // #C2AAE8 — pastel purple
 constexpr KitColor kDirAccentHot      {200, 236, 178, 255};  // #C8ECB2 — lighter pastel lime
 constexpr KitColor kDirWarn           {235, 120, 90, 255};   // #eb785a — destructive only
 
-// The envelope trace over the waveform. Two neighbours pin it at once — the lime accent it
-// crosses and bg/base behind it — which bound ANY single value to 3.07:1 against both; this is
-// that optimum, with no room in either direction. No categorical accent can carry it: every
-// one of them is light enough to fall under 2:1 against the lime.
+// The envelope trace over the waveform. Warning only (the two-neighbour rule is
+// core/ui/CLAUDE.md's): this value has NO room in either direction, and it is confined to the
+// waveform band — inside the 20%-alpha loop-span fill it already sits under floor at 2.25:1,
+// which no single value can fix.
 constexpr KitColor kDirOverlayTrace{129, 106, 166, 255};  // #816AA6 — muted violet
 
 // Spectral ramp: pastel lime (low) -> pastel teal (mid) -> pastel purple (high). The mid stop
@@ -160,6 +158,12 @@ KitColor spectralColor(double t) {
     return mix(kDirSpectralMid, kDirSpectralHi, (t - 0.5) / 0.5);
 }
 
+KitColor compositeOver(const KitColor& over, const KitColor& under, double alpha) {
+    if (alpha < 0.0) alpha = 0.0;
+    if (alpha > 1.0) alpha = 1.0;
+    return mix(under, over, alpha);
+}
+
 double relativeLuminance(const KitColor& c) {
     return 0.2126 * linearizeChannel(c.r) +
            0.7152 * linearizeChannel(c.g) +

src/core/ui/theme.h

@@ -56,7 +56,14 @@ enum class InteractionState {
     Disabled,
 };
 
-// Text size classes for the WCAG floor: "Large" (>= ~18.66px, or >= ~14px bold) and UI-state
+// WCAG 2.1's large-scale thresholds, in px at 96dpi (18pt = 24px normal, 14pt = 18.66px bold).
+// A previous revision wrote the BOLD threshold as the normal one and both ~25% low, which let
+// 15px semibold self-classify as Large and clear a floor it was not entitled to — draw sites
+// that want the Large floor static_assert their font against these.
+inline constexpr double kLargeTextMinPx     = 24.0;
+inline constexpr double kLargeTextMinBoldPx = 18.66;
+
+// Text size classes for the WCAG floor: "Large" (>= 24px, or >= ~18.66px BOLD) and UI-state
 // indicators clear at 3:1; body text clears at 4.5:1 (WCAG 2.1 AA).
 enum class TextClass {
     Body,   // AA 4.5:1
@@ -73,14 +80,26 @@ KitColor roleColorState(Role role, InteractionState state);
 
 // Spectral hue ramp for the keyboard strip: maps normalized position t in [0, 1] (low note ->
 // high note) through a pastel lime -> teal -> purple arc, so the strip reads as part of the
-// palette rather than a separate flourish. The arc is its own three stops — a categorical
-// accent move must not be able to reorder it. t is clamped to [0, 1].
+// palette rather than a separate flourish. The MID stop is its own value; lo/hi remain aliases
+// of accent/primary and accent/tertiary, so a categorical accent move can still reorder the
+// ramp — testSpectralRampLuminanceIsMonotonic is the build-time catch, not the structure.
+// t is clamped to [0, 1].
 KitColor spectralColor(double t);
 
 // --- WCAG contrast (the "punch" rule, made testable) --------------------------
 
+// The effective opaque color of `over` drawn at `alpha` on top of `under` — the composition the
+// contrast math needs before it can judge a translucent fill. alpha is clamped to [0, 1]; the
+// result carries `under`'s alpha byte.
+KitColor compositeOver(const KitColor& over, const KitColor& under, double alpha);
+
+// The waveform's loop-span fill alpha. Named HERE rather than at its draw site so the contrast
+// test composes the same value the shell draws with (see compositeOver).
+inline constexpr double kLoopSpanFillAlpha = 0.20;
+
 // Relative luminance per WCAG 2.1 (sRGB linearization + 0.2126/0.7152/0.0722 weighting). Alpha
-// is ignored — a translucent overlay's effective color is the caller's to compose first.
+// is ignored — a translucent overlay's effective color is the caller's to compose first
+// (compositeOver).
 double relativeLuminance(const KitColor& c);
 
 // WCAG contrast ratio between two colors, in [1, 21]. Symmetric.